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INTERACTIONS IN ORGANIZED MEDIA

SUMMARY

Thesis Submitted for the Degree of © o t t o r o f

IN

CHEMISTRY

Mrs. SANGEETA KUMAR

T A ^ ' ^ l / O DEPARTMENT OF CHEMISTRY

ALIGARH MUSL IM UNIVERSITY ALIGARH (INDIA)

1991

This thesis entitled "Interactions in organized media" concerns the studies of interaction of various dyes and poly-mers with surfactant solutions. A lot of literature is available on the interaction of a wide variety of substrates with surfactants. Due to their widespread uses in many in-dustrial applications there hsts been an increasing interest in the surfactant research, both academic and applied. Recently, much effort has been directed towards the utilization of orga-nized media to modify reactivity and regioselectivity of products.

The thesis comprises four chapters. General introduc-tion about the behaviour of surfactants in aqueous and non-aqueous media, factors which Effect CMC, solubilization, dyes, polymers and their interaction with surfactants are reviewed in Chapter - I. This chapter provides a survey of all the work available on solubilization, dye-surfactant and polymer-surfactant interaction.

Chapter - IX reports'^he solubilization and competitive solubilization studies on Sudan - IV and anthracene in anionic SDS, nonionic TX-lOO and cationic CTAB micellar systems in aqueous medium by spectrophotometric technique. J

From a comparison of the solubilities of Sudan - IV and Anthracene in water, organic solvents and aqueous surfactant

solution indicate that the solubility of Sudan - IV and anth-racene is much higher Ifi nricellar solutions than in bulk water also, dye solubility in the bulk organic solvent is only an order of magnitude higher than in the micellar solution, ^oles of surfactant solubilizing a mole of dye, Nj , have been calculated for both Sudan - lY and anthracene in the respec-tive surfactant solutions, which show that Nj is highest for SODS and lowest for TX-100^ Also for each of the surfactants, the value of Np is observed to be much higher for anthracene than for Sudan - IV.

In the competitive solubilization, it was found that the values of Nj are increased for both anthracene and Sudan-IV as compared to the Nj values in single solubilization experi-ment. This is to be expected since in the joint solubilizat-ion the molecules of both the dyes may be solubilized in the micelle. What is more significant is that for each of the three surfactants the value of N^ is higher for anthracene than for Sudan - IV in the joint solubilization experiment. This indicates that Sudan - IT is preferentialy solubilized than anthracene in these surfactants.

The solubilization ratios i.e. ratio of N ^ of Sudan-IV or anthracene in single solubilization and joint solubilization of experiments have been calculated. The ratios being 1.3 and 1.2 for Sudan IV and anthracene respectively. The standard free energy of dye solubilization, AG° in all the three types s

of surfactants in different media were calculated. The results of successive solubilization of Sudan - IV followed by solubilization of anthracene and successive solubilization of Sudan - IV show that the value of Nj does not change as compared to values obtained for single solubilization. The effect of nature of surfactants and solubilizate on the solubilization parameters have been discussed. The values of Nj and the aggregation numbers of the micelles have been used to calculate the number of dye molecules solubilized in the micelle for all the three surfactants. These values show that Sudan - IV" has a highest solubility in CTAB, explained by a more favourable interaction between the trimethyl ammonium head group and the hydrophobic dyes.

The conclusions are that Sudan - IV is preferentially solubilized over anthracene in all the surfactant systems.

The studies on the interaction between anionic dyes and a cationic surfactant are discussed in Chapter - III.

•^he interaction between anionic dyes, pyrocatechol violet (PCV) and Alizarin Red S (ARS) and cationic surfactant(CTAB) has been studied at 30®C in aqueous medium. Conductimetric titrations of a dilute solutions of both PCV and ARS with a concentrated solution of CTAB resulted in three distinct regions./^ Region L and 11 where complexation, precipita-tion and separation occurs were of much interest. The

concentration of lontirAplet species was determined by a method analogous to the method of "continuous variation" developed by Job. The values of ion-trvy AjiJcassociation cons-tants were for PCV and ARS res-pectively. The AG° values for interaction of both PCV and ARS with CTAB have been calculated at 30°C in the region I.

The onset of turbidity in the solution and sharp change in the slope of the conductivity curve can be des-cribed as the beginning of the formation of 1:2 insoluble

- 2

complex. Plots of dye concentration versus [CTAB] have been found to be passing through origin which prove that the insoluble complex is indeed formed in a 1:2 ratio. The mean values of solubility product were found to be S^xio and 2.34 x raol^dm"^ for PCV and ARS respectively.

Region III is characterised by the termination of region II and disappearance of turbidity. Another interesting feature is that there is a change in the gradient of conduc-tivity versus concentration of titrant plots. This change in gradient does not correspond to the CMC of CTAB. The dis-appearance of turbidity at higher concentration of CTAB can be regarded as the consequence of micellar solubilization of the complex.

The temperature dependent study of ^^^on-triplet the values of dH°, the enthalpy of complex formation. The enthalpy of complex formation of the PCV - CTAB system is exothermic.

5

Chapter - lY deals with 'the study of the polymer polyvinylpyrrolidone (PVP) with anionic surfactant, trieth-anolamine dodecyl su. Iphate by viscometric and conductomet-ric techniques. The viscosity - concentration of polymer profile shows that the polymer surfactant complex behaves as a typical polyelectrolyte. The conductometric data show that there is an increase in interaction with increasing polymer concentration^^The composition of polymer surfactant aggregates was found to be constant, 2.5:1 regardless of the concentration of PVP in solution. From the temperature dependent study the heat of micellization has been calculated at various temperatures as well as the free energy of stabi-lization of the micelle. The specific conductivity of various TDS solutions in presence of PVP of different moleculaar weights has been studied at 30°C. It is found that the con-ductivity decreases with increasing molecular weight of the polymer. The study of specific conducitivity of PVP in TDS solution at different salt concentrations at 30°C.

These studies show that TDS - PVP interaction would be partly chemical and partly physical in nature, with the hydro-phobic forces playing a major role in such an interaction.

INTERACTIONS IN ORGANIZED MEDIA

Thesis Submined for the Degree of B o t t o r o f

IN

CHEMISTRY

Mrs. SANGEETA KUMAR

DEPARTMENT OF CHEMISTRY ALIGARH MUSL IM UNIVERSITY

ALIGARH (INDIA)

199 1

Ibt. J V .

(0^ Off. : 25515 Resi. : 26316

DEPARTMENT OF CHEMISTRY Aligarh Muslim University ALIGARH-202 002, INDIA

OctobeA 1, r99I

Thl& to that the

mtUltd "WTERACriOm lU ORGAHIZEP MEVIA" U tkt

ofUQJun.al mnk c.aAMA£.d out by M^. Sangdzta.

KumA unde/L my Aapz/ixiZ&Zon and iLutabte.

^ofi ^ubnuA^Zon ion. ike, am/id o^ • ?k.V ddqtizd.

yin ChmJj>pLy.

Residence : MIG-55(P). A.D A , Ramghat Road. ALIGARH-202001

ACKUOffJLEVGEmtn'S

SpzcUZ thanks ojiz daz to M^ ûpeJit/ZdoA., VA. H.N. Singh

who oiizyuidd mcouAagzrmni and c.oru,tAactl\!Z cJuXMiyUm mXh a

lot patXmcz thAoughoat thz tznuKo. OjJ my mAk In thli,

labofioitofiy.

I am thm-kûl to Jf.A. Chapman, VzpanXmznt

oi CkmUtJiy, MlgaJih UiLSZXm , AtigoMk, ôa /KU&aAch

{âcUZXtlu. I aL(,o wl&h to thank o Va. J. P. Haunt, Reader,

VzpaAtment o^ CdimZi>tAy and Vn.. V. KumoA, RzadeA, VtpaAtmznt

?hy6-ic6, AlâAh Mu ZMn Un£veAj>Xty, kJUQank, Ion. tzttuig tne u4e thz 6pzctAomeXAMi âcIlZtCM thoMi laboAatoAiu .

1 am QxtJimzly beJioldzn tci my poAZnt^ and In-lam {ôK

th(UA Intejiejyt and zncouAogmcnt ixi my academJjz e.nd2xivoa/iA. I

thank my husband Atut and •ion Rofian ÔA thz moAoJi -iuppoAt thzy

gave mz.

I acknouit&dge. tht hzlp o^êjoizd to mz by my Âhind^,

VA. Sanjzzu KumaA, Mt. VuAga PAaâd, Ui. Vlxjya GangmA, VA.kAckana

AgaAMiaZ and VA. Uzelam ShMma among many otheAA whom It would

not bz poMlblz to mzntZon ZndC^rldaally.

t thank the. UnUveJU^y OMn-CA Can\iM^4>'Can ôa a A(U&aA.ch

gAan^t. ^ ^ y

SANGEETA KUMAR )

CONIffiS

Page

LIST OF TABLES LIST OF FIGURES LIST OF PUBLICATrONS

CHAPTER - I

GENERAL INTRODUCTION REFERENCES

CHAPTER - IL

COMPETITIVE SOLUBLIZATION OF SUDAN-IV AND ANTHRACENE IN MICELLAR SYSTEMS. EXPERIMENTAL RESULTS AND DISCUSSION REFERENCES

CHAPTER - I I I

INTERACTION BETWEEN A CATIONIC SURFACTANT AND OPPOSITELY CHARGED DYES. EXPERIMENTAL RESULTS AND DISCUSSION REFERENCES

CHAPTER - lY

INTERACTION OF POLYVINYL PYRROLIDONE WITH TRIETHANOL AMINE DODECYL SULPHATE EXPERIMENTAL RESULTS AND DISCUSSION REFERENCES

(i) (V) (ix)

1 25

35 41 44 66

70 75 77

105

109 116 119 143

(i)

CHAPTER

Table 1

LIST OF TABLES Page

- I I

Solubilities and Molar absorption coefficients of Sudan IV and Anthracene in different solvents at 30°C. 48

Table 2 Solubilization of Sudan IV and anthracene separately and both jointly in CTAB at 30°C. 49

Table 3 Solubilization of Sudan IV and anthracene separately and both jointly in TX - 100 at 30°C. 50

Table 4 Solubilization of Sudan IV and anthracene separately and both jointly in SDS at 30°C. 51

Table 5 Nj., £ and AG for the solubili-zation of Sudan TV and anthracene separately and both jointly in CTAB, TX-lOO and SDS at 30°C. 59

Table 6 Successive solubilization of Sudan IV followed by anthracene and that of anthracene followed by Sudan lY in CTAB, TX-lOO and SDS at 30°C. 64

CHAPTER

Table 1

- H I

Specific conductivity data of PCV at various concentrations of CTAB at 30°C. 78

Table 2 Specific conductivity data of ARS at various concentrations of CTAB at see. 100

(ii)

Table 3 : Specific conductivity data of CTAB -4

in presence of 5 x 10 M PCV at various temperatures.

82

Table 4 : Specific conductivity data of CTAB _4 ill presence of 2 x 10 M ARS at various temperatures. 83

Table 5 : Specific conductivity data of PCV, CTAB and PCV - CTAB in water at various temperatures. 87

Table 6 ; Specific conductivity data of various concentrations of ARS, CTAB and ARS-CTAB in water at various temperatures. 88

Table 7 : Data for the [dye] versus [CTAB] 2 and log [CTAB] versus log [dye] plots at 30°C.

- 2

91

Table 8 : Ion triplet association constants, ^ion-triplet» standard free energy change, AG", enthalphy, AH° and entropy, AS° for PCV (5 x 10~^M) 'at 30°C, 35°C and 40°C. 98

Table 9 : Ion triplet association constants, ^ion-triplet' standard free energy change, AG°, enthalpy, aH° and entropy, AS" for ARS (2 x 10"^' at 30®C, 35®C and 40°C.

'M) 99

Table 10: Specific conductivity of CTAB in -4

presence of 5 x 10 M PCV and in water alone at various temperatures, 100

(iii)

Table 11 r Specific conductivity of CTAB in presence of 2 x.10 M ARS and in water alone at various temperatures; 101

CHAPTER - IV

Table 1 Viscosity results of TDS solutions at various concentrations of PVP (K-90) at 30°C. 120

Table 2 : Specific conductance of various concentrations of TDS in presence of different concentrations of PVP (K-90) at 30°C. 124

Table 3 : Specific conductance of various concentrations of TDS in absence and presence of 0.5% PVP in ImM NaCl at various temperatures. 130

Table 4 : Variation of CMC of TDS and T at different temperatures in the presence of 0.5? PVP in ImM NaCl. 132

Table 5 The heat of micellization(AH ) of TDS in xmM NaCl solution and the heat of complex formation (AH„) of TDS with 0.5% PVP(K-90) In ImM NaCl. 133

Table 6 Variation of T in T^.CMC and AG with temperature. 135

Table 7 : Specific conductance of diffe-rent concentrations of TDS in presence of 0.5% PVP of diffe-rent molecular weights at 30°C, 100

(iv)

Table 8 i Variation of specific conductance of TDS solutions in 0.5% PVP(K-90) in presence of different concen-trations of NaCl at 30°C. :: 140

(xvi)

CHAPTER - I

Figure 1

LIST OF FIGURES

Page

Variation of physico-chemical properties with surfactant concentration.

Figure 2(a) : Hartley model of a spherical micelle.

Figure 2(b)

Figure 3

Reverse micelle.

A cross section of an aqueous normal micelle with different solubilization sites. 15

Figure 4 Various models of polymer-surfactant interaction. 24

CHAPTER - I t

Figure 1(a) Spectra of Sudan-IV in various solvents and surfactants. 45

Figure 1(b) Spectra of anthracene in various solvents & surfactants. 46

Figure 2 Calibration curve for the molar absorption coefficients of Sudan IV in (a) surfactant in aqueous medium (b) organic solvents. 47

Figure 2 Variation of absorbance of Sudan IV in solubilization of (a) Sudan IV only (b) Sudan IV and anthracene jointly in different concentrations of CTAB at 30°C. 81

(vi)

Page Figure 4 t Variation of absorbance of Sudan IV

in solubilillation of (a) Sudan IV only (b) Sudan IV and anthracene jointly in different concentrations of Triton X-100 at 30°C. :

Figure 5 : Variation of absorbance of Sudan IV in solubilization of (a) Sudan IV only (b) Sudan IV and anthracene jointly in different concentrations of SDS at 30°C. :

53

54

Figure 6 Variation of absorbance of anthra-cene in solubilization of (a) anthracene only (b) Sudan IV and anthracene jointly in different concentrations of CTAB at 30°C. : 55

Figure 7 t Variation of absorbance of anthra-cene in solubilization of (a) anthracene only (b) Sudan IV and anthracene jointly in different concentrations of TX-lOO at 30°C. 56

Figure 8 Variation of absorbance of anthra-cene in solubilization of (a) anth-racene only (b) Sudan IV and anth-racene jointly in different con-centrations of SDS at 30°C. 57

CHAPTER - ILL

Figure 1 Plots of specific conductivity versus [CTAB] in presence of various concentrations of PCV at 30°C. 80

Figure 2 Plots of specific conductivity versus [CTAB] in presence of various concentration of ARS at 30°C. 81

Figure 3 Plots of specific conductivity versus [CTAB] added in presence of O.SmM: PCV at different tem-peratures.

(vii)

Page

84

Figure 4 Plots of specific conductivity versus [CTAB] added in presence of 0.2 mM ARS at different temperatures. 85

Figure 5 : Specific conductivity versus mole fraction plots for ARS -CTAB system at 30°C, 35°C & 40°C. 89

Figure 6 t Specific conductivity versus mole fraction plots for ARS-CTAB system at 30°C, 35°C and 40''C. 90

Figure 7 Plots of (a) [dye] versus „ [CTAB]'^ at 30®C (b) log [CTAB]"'^ versus log [dye] at 30°C. 92

CHARTER - IV

Figure 1 Variation of reduced viscosity with PVP (K-90) concentration at various co-ncentration df: TDS at 30°C. 121

Figure 2 Variation of reduced viscosity with TDS concentration at various concentration of PVP (K-90) at 30°C. : 122

Figure 3 Variation of specific conducti-vity with TDS conce-ntration at different coacentrations of PVP (K-90) at 30°C. 125

(viii)

Figure 4 r Effect of PVP (K-90) on TDS at the second transition and the concentration of TDS consumed in the formation of polymer surfactant complex at 30°C. 128

•Figure 5 i The effect of temperature on the specific conductivity versus concentration of TDS in ImM NaCl solution in the absence and presence of 0.5% PVP. :; 131

Figure 6a r The effect of temperature on the CMC in 0.001 M NaCl solu-

Tg and T^ minus CMC tion, T in the presence of 0.5% PVP in O.OOIM NaCl solution. 134

Figure 6b : Variation of In CMC and In T at various temperatures. 134

Figure 7 Variation of specific conduc-tivity with TDS co.ncentration at 0.5% polymer conc" . of various molecular weights. 138

Figure 8 t Effect of salt on specific conductivity versus TDS con-centration at 30°C. 141

(ix)

LISI__OF__PyBLICAIIONS

(1) Competitive solubilization of Sudan IV and Anthracene in Micellar Systems. (Communicated)

(2) Interaction of anionic dyes with a cationic surfactant in aqueous medium. (Communicated)

(3) Interaction of polyvinyl pyrrolidone with triethanolaminelauryl sulphate. (Communicated)

( x )

UST_OF^PAEERS_PRESENTED_LN_CON^

1. Competitive solubilization of Sudan IV and anthracene in organized media. In 4th National Conference on Surfactants, Emulsions and Biocolloids, I.I.T., Bombay, Dec. 11-13, 1989 (Abstract No : P 2405, p. 36).

2. Interaction of Anionic dyes with a cationic surfactant iji Aqueous medium. In 4th National Conference on Surfactants, Emulsions and Biocolloids, I.r.T., Bombay, Dec. 11-13, 1989 ( Abstract No r 2401, p. 38 ).

3. The interaction of Polyvinyl pyrrolidone (PVP) and Triethanolamtne lauryl sulphate (TLS). In 5th National Conference on Surfactants, Emulsions and Biocolloids, M.S. University, Baroda, Oct. 28 - 30, 1991 ( Accepted ).

CHAPTER - I

GENERAL miRODUCTlON

There is considerable interest in the nature of the structural organization of multimolecular assemblies of amphiphilic molecules. Recently, much effort has been direc-ted towards the utilization of organized media to modify reactivity and regio selectivity of products. Among the many ordered or constrained systems utilized to organize the reac-tants the notable ones are micelles,microemulsions,liquid crystals, monolayers and solid phases such as adsorbed sur-faces and crystals. Judicious selection of a given organized system for a given application requires a sufficient under-standing of the properties of the organized media themselves and those of the substrate interactions therein. Due to their widespread uses in many industrial applications there has been an increasing interest in the surfactant organized assemblies both from academic and applied point of view. A fundamental understanding of the physical chemistry of surfactant organi-zed assemblies, their unusual properties and phase behaviour is essential for most industrial chemists.

Surfactants,surface active agents, also called deter-gents, are amphiphilic organic or organometallie molecules wiiere

a polar head group attached to a long non polar tail provides (1-3)

distinct hydrophilic and hydrophobic functionalities .Owing to the polarity of the distinct regions these substance have also been referred to as anphipathic, heteropolax or polar non-polar

4 5 substances.' The polar nonpolar character is responsible for the unique properties of surfactant molecules in solu-tion which render possible applications in detergency, clean-ing, wetting, flotation, emulsification, dispersion, foaming

6 — 10

etc. ~ The factor responsible for desired surface activity is the balance between lyophobic and lyophilic characteristics of the moleculesf^ Aqueous solutions of surfactants or amphi-pathic molecules, at a minimum concentration, referred to as critical micelle concentration (CMC), associate dynamically to form normal m i c e l l e s . C r i t i c a l micelle concentra-tion, CMC, is a narrow range of concentration at which the micelles first become detectable. A finite abrupt change in the physical properties as a function of concentration at definite concentration of a surfactant led to the concept of CMC: (Figure 1)

The reason why do micelles form may be explained by taking into account the changes occuring when a monomer is transferred from its aqueous environment into the micelle. On transferring the monomer into the micelle, the high energy of the hydrocarbon/water interface is lost, as the chain is now in contact with other molecules of a like nature. Transfer of monomer into the micelle also means that the structuring of water around the hydrocarbon part of the monomer is lost, therefore an ordered state has become a disordered one with regard to water, implying a positive entropy change and a

di Cl o I. Q. O o E

o u 'I c Q.

o s m o t i c p r e s s u r e

s o l u b i l i z a t i o n

m a g n e t i c r e s o n a n c o

S u r t o c i a n t c o n c e n t r a t i o n

Plg.1 v a r i a t i o n ot Phyt i c© - c h c m l c a i p rop«r t i » s with

sur foctont c o n c e n t r a t i o n

decrease in free energy. The factor opposing the micelle formation in ionized surfactant is the rise in free energy due to electrical work and translational freedom losses due to incorporation of monomer into a micelle. This disordered to ordered transition gives a negative entropy change which will oppose the positive entropy changes occurring from losses of water structure. The overall decrease in free energy due to loss of hydrocarbon/water interfacial energy and water structure outweighs the free energy rise due to electrical work and translational freedom losses, giving a remarkable tendency to micellize. The sharpness of the break in physical properties depends on the nature of the micelle and on the

(13) method of CMC determination. Mukherjee and Mysels have compiled CMC data of various class of surfactants using diffe-rent techniques. NORMAL_MICELLES

Aqueous solutions of surfactant molecules, at CMC, associate dynamically to form normal micelles. Such micelles are thought to be roughly spherical^^'^"^'^^^ A schematic two dimensional representation of an ionic spherical micelle is shown in Fig. 2(a). The hydrophobic part of the aggregate forms the core of the micelle while the polar head groups are located at the micelle - water interface in contact with and hydrated by a number of water molecules. The interior of a micelle is viewed as being much like a liquid hydrocarbon

6

I M(c«Uar core

. _ _ Hyd roca rbon I " - " — " - ! " interior

A q u e o u s ep^terior

Gouy - Chapman layer

V Stern layer

Fig, 2 ( a ) Hart ley model of o s p h e r i c a l micelle

droplet. Fluorescence and esr measurements on the rate of rotational reorientation of probe molecules in micelles in-dicate that this is substantially true even though their motion is significantly restricted relative to that in pure organic solvents of low viscosity.

The micellar surface appears to be an amphipathic structure which is supported by the binding of both hydropho-bic organic molecules and hydrophilic ions with micelles.The amphipathicity is a property shared with the surfaces of pro-

C16) teins and membranes.

The surface of micelles formed from ionic surfactants is highly charged(3-5 molar). About 80% of these charges are neutralized directly through the incorporation of counter ions into the micellar surface, forming the stern layer. The remainder of the counter ions form the diffuse Gouy Chapman layer. The existence of a substantial net charge at the mice-llar surface provides a large dip in electrical potential across the stem layer and attracts ions of. opposite charge. The amount of water in the micellar interior varies from sur-factant to surfactant. Water is considered, at present, to penetrate the micellar surface only upto distances of approxi-mately three to six carbon atoms. It has been proposed that micelles are loose and porous structures in which water and

(17, 18) hydrophobic regions are constantly in contact with each other.

8

REVERSE_MICELLES

In Aon polar solvents, in the presence of traces of water, surfactants associate to form the so called reverse/ inverted micelles. The polar head groups form the interior while the hydrophobic hydrocarbon moieties of the surfactants are in contact with the apolar solvent. The size and proper-ties of reversed micelles vary with the amount of water

(5,19-21) present .

The inner cavity of reverse micelles has been compared (22)

with the active sites of enzymes. Water in reverse micelles is expected to behave very differently from ordinary water because of extensive binding and orientation effects induced

(23) by the polar heads forming the water core. Lately enzymes have been encapsulated inside the water pool of the reverse

(24) micelle without affecting their activity. Reverse micelles are able to solubilize hydrophiLic molecules like enzymes and plasmids that are much larger than the original water pool diameter. Such micelles can be viewed as novel microreactors whose physical properties can be controlled through the water content.

Techniques to determine the CMC of reversed micellar (25 26) systems include dye solubilization ' , water solubiliza-

(27) (28) ^ (29) . ^ . (25,29,30) tion, ^ nmr,^ ^ solubility,^ surface tension^ ' ' (14)

and others which have been compiled by Shinoda . A possi-ble structure of reversed micelle in a nonpolar medium is shown in Figure 2(b).

9

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10

FACTpRS_AFFECTING_CRITICAL_^ AND MICELLE

SIZE

The value of CMC is dependent upon a large number of parameters like total carbon chain length, additional polar groups, C = C double bonds, chain branching of surfactants and various types of additives; polar and nonpolar,electro-

f 14 lytes, temperature and pressure. '

The CMC and micelle size depend on the length of the hydrocarbon chain,generally the CMC decreases as the hydrocar-bon chain length increases. For a homologous series of sur-factants, the CMC is related to the number (m) of carbon atoms in a straight hydrocarbon chain by

log CMC = A - Bm (1)

where A, B are constants for a homologous series and value of (14)

these constants are listed by Shinoda . Lengthening of the hydrocarbon chain causes an increase in the micelle size and aggregation number.

The position of the head groups also affects the CMC; closer it is to the centre of the chain, higher the CMC. The presence of double bond also causes an increase in CMC.

The addition of salts decreases the CMC of ionic deter-gents, while the micelle size increases.For non ionic detergents the addition of salts slightly decreases the CMC and further increases it at higher salt concentration. Non electrolytes

11

like urea and its derivatives increase the CMC of ionic and nonionic surfactants, which are generally believed to be water structure breakers. Addition of acetamide and forma-mide decreases the CMC of surfactants.

For ionic detergents the CMC first decreases upto a certain temperature and then increases at high temperaturSs^^ For nonionic detergents the CMC decreases with increasing temperature.

The CMC has been found to increase upto a pressure of 1,000 atmospheres and decrease with further increase of pressure,

THE0RIES_gF_MICELLrZAT10N

Micelle formation has been treated mainly by applying (2,31-33)

the law of mass action to the equilibrium between monomers and aggregates or by considering the micelle as a separate but

(33,34) soluble phase.

The law of mass action treatment predicts the increase in the monomer concentration, although at reduced rate, above the CMC. It is incapable, however, of accounting for variation in aggregation numbers and it is inapplicable to multi component micelles and systems including solubilizates.

An alternative approach to the above model is the pseudo phase model which assumes the formation of a pseudo or second phase at the CMC above which the concentration of monomers remains constant. The process of micellization involves the

12

reversible aggregation of N amphiphile molecules,(monomers,ra) to form a micelle (M) given as

Nm M (4)

neglecting the activity coefficients, the equilibrium constant of this process may be written as

K, = ^ (5)

This model considers micelle formation as analogous to a phase separation and the CMC is then the saturation concen-tration of the amphiphile in the monomeric state whereas the micelles constitute the separated pseudophase. This model predicts a sharp change in physico-chemical properties around the CMC. However, a closer analysis of experimental data reveals a smooth transition and, furthermore, the monomer concentration and activity are not constant above the CMC.

The term solubilization implies the formation of a ther-modynamically stable isotropic solution of a substrate ( the solubilizate), normally Insoluble or only slightly soluble in a

(35) given solvent, by the addition of a surfactant (the solubilizer). Solubilization is of course, closely related to micellization since little or no solubility increase is observed until the CMC of the surfactant is reached, but once the micelles are fully formed its increase is directly proportional to the con-

13

centration of the surfactant over a large range. The observa-tion of solubility changes as a function of surfactant concen-tration has, in fact, led to the determination of numerous CMC values. The observed solubility data is expressed as solubility curves or as phase diagrams^^^^

The nature of the solubilizate as well as that of the solubilizer and the solvent, the presence of additional polar or nonpolar substrates, and the temperature are the complex parameters which influence solubilization. Counter ions of micellar surfactants, added electrolytes and non-electrolytes also influence solubilization. Several formulae have been suggested for relating CMC's to the size of the hydrophobic

(14,37) moiety of the surfactant for a given hydrophilic entity , in all cases the CMC decreases as the homologous series is ascended. Unfortunately, the effect of chain length on solu-bilizing power is not quite as simple to interpret for the additional complicating factor of the solubilizate must be considered. The complex procedure of incorporation of the various types of solubilizate and the subsequent size of the solubilizate surfactant micelle makes any generalization on this problem extremely difficult. For a nonionic detergent, provided that there is a sufficiently long polyoxyethylene chain to give a stable aqueous solution, further increased glycol chain length does not enhance the solubilizing power.

The micellar solubilization with temperature depends on

14

the structure of the solubilizate and surfactant, and in most cases increases with increasing temperature. This effect can generally be ascribed either to (1) a change in the aqueous solubility of the solubilizate and (2) a change in the proper-ties of the micelles. With the ionic detergents, the maximum additive concentration increases with temperature. Micellar weights measured at various temperatures show that both the nvimber of surfactant monomers and the number of solubilizate molecules per micelle increased with temperature. The effect of addition of electrolytes on solubilization has many important consequences and has been studied extensively. In general it has been that with increasing concentration of counter ion the CMC decreases leading to increase in increased micellar

(38, 39) size with the concomitant increase in solublization. The location of solubilization sites of solubilizates within mice-lles in aqueous solution has recently been the object of many (2,40,41) spectroscopic studies by various techniques. In general the site of incorporation of solubllized molecules depends on their relative hydrophobic and hydrophiiic tendencies. The solubili-zate may be entrapped in the hydrocarbon core of the micelles, be oriented radially in the micelle with its polar head buried (deep penetration) or near the surface (short penetration) or (42-52) be absorbed on the surface of the micelle. (figure 3) Additionally, for non-ionic surfactants, incorporation of the solubilizate can occur in the polyoxyethylene shell of the surfactants.

15

BULK WATER

Fig. 3 A c ro s s section of an aqueou s normal micelle with different s o l ub i l i z a t i on s ite, A and B represent same and opposite charge solute to the micelle while C and D represent the nonpolar and amphiphi l ic s o l u t e s .

16

Many techniques have been employed to study the sites of solubilization. Distribution studies, X-ray diffraction,

(2,53,54) (55) NMR, spin labelling techniques. Ultrasonic spectroscopy,

(56) (57,58) Raman spectroscopy, electron spin echo modulation study, optical activity, viscosity and conductivity of trace electro-(59) (2)

lytes and absorption spectroscopy.

APPLICATIONS OF SOLUBILIZATION

With the large scale introduction of surface active agents and the discovery of phenamenon of micellar solubiliza-

(60,61) (62) (63) tion, the pharmaceutical, biological, chemical, and industrial applications have become obvious. Solubilization also finds

(64) (65) use in cosmetic preparations, separation science, enhanced oil

(65) recovery and conversion of energy from one form to another.

Solubilization in reverse micelles plays a vital role in removing polar dirt from clothes, in motor oils to solubi-lize corrosive oxidation products and to prevent them from reacting with engine parts., Solubilized systems are used in agricultural sprays, dyeing media, in removing odour causing molecules from food packaging plants, photographic processes and in surfactant type corrosion inhibitors. A very important

(65) application of solubilization is in separation science. Aqueous micellar systems have the ability to solubilize, compartmen-talize and concentrate (or separate,) solutes, alter the local environment about associated solutes, alter the position of

17

equilibrium systems and alter the photophysical and chemical pathways and rates among others. Although all of these mice-liar features can be exploited to aid the separation scientist in specific instances, the main basis for the successful uti-lization of aqueous micellar media in separation stems from the fact that they can differentially solubilize and incorpo-rate a variety of solutes. Some of these are micellar faci-litated sampling considerations, extractions based on the differential solubilizing ability of micelles, micellar elec-trokinetic capillary chromatography, micellar liquid chromato-graphy, micellar enhanced detection, micellar enhanced ultra-filtration, and micelle mediated extractions or preconcentra-tions of polyaromatic hydrocarbons.

INTERACTION_BETWEEN_LARGE_ORG

Recently there have been several studies on interactions (67-71)

between large organic cations and anions. This interaction is an important factor to be considered when applying physico-chemical principles to the design of pharmaceutical dosage and drug availability. The extensive use of ionic surfactants in pharmacy for solubilization, preservation and stabilization in the presence of other additives or drugs of opposite charge may

(15,72-73) result in several desirable or undesirable interactions. Numerous studies on the influence of surfactants on drug and dye absorption have shown them to be capable of increasing or

18

exerting no effect on the transfer of drugs across biological (74-79)

membranes. Depending on the nature of the cation and anion, ion pair formation, complexation, coacervation and precipita-tion can all be ascribed to such systems. It has been reported that the types of possible interactions occurring between large organic ions of opposite charge in aqueous medium depend on the ( 6 6 )

factors such as electrostatic and hydrophobic forces. The stoichiometry of these interactions have been determined using conductimetric and turbidimetrie methods. POLYMERS

In recent years increasing use has been made of synthe-(80)

tic polymers in a wide variety of related applications. The term "polymer" denotes a substance whose molecules are composed of a large number of similar (if not identical) units covalently linked. The units so linked are termed "monomer units" or "mer units". If the mer units are essentially or nominally identical then they form a "homopolymer", with mer units of two or more types a "copolymer" results.

The number of mer units in a particular polymer molecule is termed the degree of polymerization. The degree of polymeri-zation is determined by dividing the molecular weight of the (81) macromolecule by the average molecular weight of the monomer. The degree of polymerization may vary over a wide range, from a few units to 5000 - 10,000 and more. Polymers with a high

19

degree of polymerisation are called high polymers, while those with a low degree of polymerisation are known as oligomers.The

4 molecular masses of high polymers are of the order of 10 to 10 , and hence, are high molecular compounds. Oligomers are polymers with a molecular mass of 500 - 6000. To name a few common polymers, poly(ethylene oxide). Poly (ethylene glycols). Polyvinyl Alcohol, Polyvinyl pyrrolidone are a few common ones.

The structure of PVP with an . amide group ( or more strictly, an imide group) in each chain unit together with hydrophobic methylene and methine groups, thus shows certain similarities to the poly peptide chain of proteins, where, how-ever, the amide groups are in the back bone of the polymer and any hydrophobic groups pendant from it. These similarities of structure between the two as well as similarities in behaviour such as protective action towards colloids and dispersions, and PVP's marked reversible binding power toward small -

molecule solutes has led to suggestions that it may be viewed (80, 82, 83)

as a model compound for the proteins.

CHg CH

N. CH. •c=o

CH2 CHg n

polyvinyl pyrrolidone

20

A??LiCATIONS_OF_POLYMERS

Polymers have got immense use and their applications are (84)

tremendous. A variety of natural, semisynthetic and synthetic polymers have been proposed as plasma substit^^^^. Prominent among the synthetic polymers so proposed is PVP. David and

(86) Gavendo have found PVP to be useful as a protective agent in the freeze preservation of whole blood. They have also studied the protective action of PVP toward thermal and mechanical damage of red blood cells.

Polymer membranes are applied in the purification and treatment of water and aqueous systems by processes such as

(87, 88) electrodialysis and hyper filtration (reverse osmosis).

Polymers find immense applications in paints, coatings, emulsion paints, fibres, textiles, fabrics, production of films and sheets, polymeric foams, reinforced plastics, laminates,

(89-95) adhesives and cosmetics.

Wherever surfactants are employed, they are mixed with various substances for improving their performance. The inter-action of macromolecules and amphiphilic small molecules is of importance in a wide variety of biological systems and indus-trial processes. In recent years, polymer - surfactant solutions have been the topic of a large number of investigations, and the solution aspects of these mixtures have been reviewed

21

(92-95) extensively. Polymer surfactant interactions are also of con-siderable interest for fundamental studies, because they combine the effects of ionic, dipolar, and hydrophobic interactions,and the aggregates formed provide a new microenvironment.

Polymer surfactant interactions may result in changes of (96)

conformation of polymer chains. The unfolding of globular pro-teins in the presence of surfactants is partly due to such interactions.

Investigations of polymer surfactant complexes are parti-cularly gennane to two distinct areas of application. Dilute solutions of polymers and micelles are used conjointly in

(97) enhanced oil recovery. Also the state of association of natural polymers and detergents - i.e., proteins and phospholipids presumably influences the properties of biological membranes. The elucidation of interactions in such complex assemblies may be prohibitively difficult, thus suggesting the use of model (80)

systems ccsnprised of synthetic compounds. Polymer surfactant interactions also play an important role in detergency, where the antiredeposition agents, used to improve the detergency by avoiding the soil redeposition during the rinsing cycle, are (98) water - soluble polymers.

Lately the significant contributions of the coulombic forces in the biriding were disclaimed and the binding of un-

(99-103) charged polymers such as Polyvinyl Alcohol (PVA), Polyethylene

22

(103-116) (103,111,114,115,117-124) (125-126) (115,127) oxide(PEO), and Polyvinyl pyrrolidone (PVP), PEG, PVAc, came into recognition. In these systems prominent electrosta-tic forces were absent and only the hydrophobic forces were present. Later it was found that anionic surfactants had strong interaction with various nonionic polymers. On the contrary cationic and non-ionic surfactants showed little or no sign of

(128) interaction at all. However, in nonionic polymer - cationic

(109,115,128-131) surfactant systems counter ions played a crucial role. For example addition of anionic surfactants raised the viscosity of a solution of nonionic polymer like PVP and polyvinyl Alcohol-Acetate copolymer (PVA - Ac) remarkably. On the other hand the cationic surfactants showed a decrease of viscosity in the very low concentration region and a sharp upturn in the higher con-

(115,129) centration region. This behaviour arises due to binding of SCN~ or I~ to the polymer initially as ion pair for inducing further binding of more surfactant cations, but hydrophobic counterions such as ethyl sulphate or butyl sulphate did not show any indu-

(115) (100-102,107, cing effect for binding of cationic surfactants. Viscosity as 115,124,129,132,133) (11,123) well as calorimetry measurements indicate that inter-actions cannot be explained entirely on the basis of hydrophobic interaction. Recently NMR studies have revealed that methylenes adjacent to the anionic head group are involved in the binding to (107,116,130) PEO.

(104,109,110,112,125,126,133) (108,114) Other techniques like electrical conductivity, fluorescence quenching

23

(117,118,124) (105) (118,125) electrical dialysis, gel filtration, surface tension ,

(137) (110,125) (113,118,124-electrophoretic mobility, pH measurements , solubiliza-126,133) (135) (136) tion , circular dichroism spectra , Phase studies,

(120) (121) electrical birefingence and ESR had been used to study the

(119,127) polymer-sUrfactant interaction. Several workers have studied the effect of salt on polymer surfactant interaction. They observed that the high value of the reduced viscosity of a dilute solution of a polyelectrolyte in the absence of added salt decreases with the increase of ionic strength and the transition points on the surface tension - surfactant concentra-tion curves were lowered with increasing salt. An increase in the surfactant alkyl chain length has the effect of enhancing

(95,111,113) the polymer micelle interaction.

Polymer - surfactant systems in aqueous media are therefore a special case of polymer - ion systems in various solvents, and only the micellizing ability of the cosolute makes the appearance of interactions more remarkable and distinctive. Different models of polymers - surfactant interaction are shown in.figure.(4).

24

11

in IV

FIG.A. VARIOUS MODELS OF POLYMER - SURFACTANT I N T E R A C T I O N

25

B-E_F_E_B_iJ_C_E_S

1. G.S. Hartley, "Aqueous Solutious of Paraffin chain Salts", Herman etcie, Paris (1936).

2. J.H. Fendler and E.J. Fendler, "Catalysis in micellar and Macromolecular systems". Academic Press, NY (1975)

3. J.K. Thomas, "The chemistry of excitation at surfaces", American Chemical Society, Washington D.C.,(1984).

4. J.W. McBain "Colloid Science", D.C. Heath and Co., Boston (1950).

5. K.J. Mysels, "Introduction to colloid chemistry", Interscience, Rub Inc. NY (1959).

6. M.J. Schick, Journal Colloid Sci., 17, 801(1963). 7. M.J. Schwuger, J. Am. Oil. Chemists. Soc., 59,

258 (1982). 8. J. Leja, "Surface Chemsitry of Froth flotation". Plenum,

NY (1982). 9. R.H. Ottewill, "Non ionic surfactants" (M.J.Schick,Ed)

.Dekker, NY (1967). 10. P.Mukerjee, "Solution Chemistry of Surfactants" (K.L.

Mittal, Ed,") Plenum Press, NY 1959. 11. T. Tadros, Ed., "Surfactants" , Academic Press NY(1984). 12. J.W. McBain, Trans. Faraday Soc., 9, 99 (1913). 13. P. Mukerjee and K.J. Mysels, "Critical Micelle concen-

trations of Aqueous surfactant systems", NSRDS, (1971).

26

14. K. Shinoda, T. Nakagawa, B. Tamamushi and T. Isemura, "Colloidal surfactants. Some Physico-Chetnical Proper-ties" Acad Press, NY (1963).

15. P.H. Elworthy, A.T. Florence and C.B. Mac-Farlane, "Solubilization by surface active agents", Chapman and Hall (London) (1968).

16. E.H. Cordes, Pure and Appl. Chem.,^, (7), 617. 17. P. Fromjerz, Chem. Phys. Lett., 77, 460 (1981). 18. F.M. Menger and D.W. Doll, J. Am. Chem. Soc., IOC,

1109 (1984). 19. J.H. Fendler, J. Phys. Chem., 1485 (1980). 20. J.H. Fendler, Acc. Chem. Res., 2, 153 (1976). 21. K. Kon-No, H. Asano and A. Kitahara, Prog. Colloid

Polymer Sci., 20(1983). 22. J.H. Fendler, Acc. Chem. Res., 13, 7, (1980);Y.M.Tricot,

D. Furlong, S. Nail and H.F. Wolfgang, Aust. J. Chem., 37 (6) , 1147 (1984).

23. P.L. Luisi and B.E. Straube (Eds), "Reverse micelles". Plenum New York (1984).

24. Ph.D. Thesis of Dr. Ajay Kumar, IIT Kanpur (1989). 25. M. Wentz, W.H. Smith and A.R. Martin J. Colloid Inter-

face Sci., 36 (1969). 26. H. Saito and K. Shinoda, J. Colloid Interface Sci.,

359 (1971). 27. J.F.Yan and M.B. Palmer, J. Colloid Interface Sci^

177 (1969).

27

28. K.N. Mehrotra, Y.P. Mehta and T.N. Nagar, J. Prakt. Chem. , W , 607 (1971).

29. ibid, 545 (1970). 30. G. Scibona, P.R. Donesi, A. Conte and B. Seuppa, J.

Colloid Interface Sci. , 631 (1971). 31. "Surfactants", edited by Th. F. Tadros, Acad Press Inc,

London (1984). 32. B. Lindman and H. Wennerstrom, Topics in current chemis-

try,^, 32 (1980) Springer Verleg, Berlin. 33. R.F. Kamrath and E.I. Franses, J. Phys. Chem.,

2695 (1985). 34. K.S. Birdi in, "Micellization, Solubilization and Micro-

emulsions", 'Vol. I, K.L. Mittal editor, Plenum Press, New York and London (1976).

35. K.S. Birdi, Colloid Polymer Sci^ 2 ^ , 551 (1974). 36. M.E.L. McBain and E. Hutchinson, "Solubilization and

Related Phenomena", P. 75, Acad. Press, New York (1955) 37. H.B. Klevens, J. Amer. Oil Chemists Soc. , 74(1953). 38. J.W. McBain and J.J. O'Connor, J. Amer. Chem. Soc.,

62, 2855 (1940). 39. R.C. Merrill and R. Getty, J. Phys. Colloid Chemistry,

"^74 (1948). 40. P. Mukherjee and J.R. Cardinal, J. Phys. Chem.,

1620 (1978).

28

41. B. Lindman and H. Wennerstrom in "Solution Chemistry of surfactants; theoretical and applied aspects", edited by E.J. Fender and K.L. Mittal, Plenum Press, New York.

42. J.S. Binford, Jr, M.S. Rao, V. Pollock and R.C,Malloy, J. Phys. Chem. , 3522 (1988).

43. T. Imae, A. Abe, Y. Taniguchi and S. Ikeda, J.Colloid Interface Sci., 109 (2), 567 (1986).

44. K. Ogino, M. Abe and N. Takesita, Bull.Chem. See. Jpn. , 3679 (1976).

45. T.S. Trakova, N.N. Tslkurina and Z.R. Markina., Kolloidyni Zhurhal, 34(6), 844 (1972).

46. P.A. Demchenko and N.A. Yaroshenko, Kolloidyni Zhiimal, '35 (4), 751 (1973).

47. R. Ya. Krasnosh chekova, M.Y Gubergrits and F. Peren, ibid, 48 (1), 46 (1986).

48. M. Gonzalez, J. Vera, E.B. Abuin and E.A. Lissi., J. Colloid Interface Sci., 98 (1), 152 (1984).

49. S. Singh and H.N. Singh, J. Surf. Sci. Tech. 2(2), 71 (1987).

50. P. Lianos. M.L. Viriot and R. Zana J. Phys. Chem., 1098 (1984).

51. A. Datyner, J. Colloid Interface Sci, 65 (3), 527 (1978).

52. K.S. Birdi and T. Magnusson, J. Colloid and Polymer Sci. ,254, 1059 (1976).

29

53. S. Ghosh, M. Petrin and A.H. Maki, J. Phys. Chem., 90, 5206 (1986).

54. S.Ghosh, A.H. Maki and M. Petrin, ibid, 90 , 5210(1986). 55. D.J. Jobe, V.C. Reinsborough and P.J. White., Can.

Jour. Chem., 60, 279 (1982). 56. L.B. Shih and R.W. Williams., J. Phys. Chem., 90,

1615(1986). 57. E. Szajdzinska - Pietek, R. Maldonado and L. Kevan,

J. Colloid Interface Sci., 110 (2), 514 (1986). 58. Piero Baglioni and L. Kevan, J. Phys. Chem., 91,

1516 (1987). 59. G. Roux and A. Yiallard, J. Colloid Interface Sci.,

295 (1977). 60. Mulley, in '^Advances in Pharmaceutical Sciences",

Vol. I ed by Bean, Beckett and Carless. Academic Press New York, (1964).

61. J. Swarbrick, J. Pharm. ScL, 1229 (1965). 62. V. Belle in 'Cholesterol, Bile acids and Atherscelerosis'

Elsevier, Amsterdam (1964). 63. I.M. Kolthoff and W.F. Johnson, J. Amer. Chem. Soc.,

73, 4563, (1951). 64. C.D. Moore and M. Bell, Soap Perfum. Cosmet.,^, 69(1957). 65. W.L. Hinze and D.W. Armstrong, Eds, "Ordered Media in

Chemical Separations", American Chemical Society, Washington (1987).

30

66. G.I. Muckhayer and S.S, Devis, J. Colloid Interface Sci. , 224 (1975).

67. ibid, 350 (1976). 68. ibid, 350 (1977). 69. ibid, 65, 210 (1978). 70. ibid, 66, 335 (1978). 71. ibid, 61, 582 (1977). 72. G. Schuster and H.K. Modde, Ammer Perfumes and Cosmetics,

86, (1971).

73. H. Nogami, J. Hasegawa and M. Iwatsuru,Chem. Pharm. Bull. ,18, 2297 (1970).

74. H.N. Singh and W.L. Hinze, A n a l y s t , 1 0 7 3 (1982). 75. K.S. Ambe and F.L. Crane, Science, 129, 99 (1959). 76. W.U. Malik and S.P. Verma, J. Phys. Chem., 70, 26(1966). 77. R.L. Reevs, R.S. Kaiser and H.W. Mask, J. Colloid'

Interface Science, 45, 396 (1973). 78. P. Mukerjee and K.J. Mysels. J. Am. Chem. Soc., 77,

2937 (1955). 79. F.A. Green and S. Fleischer, Biochemical and Biophys.

Acta, 70, 554 (1963). 80. Philip Molyneux, in "Water - A Comprehensive Treatise"

Vol. 4, Plenum Press, page 569, New York and London, 1975.

81. A.Tager, in "Physical Chemistry of Polymers" Mir Publishers, Moscow, 1978.

82. B. Jirgensons, J. Polymer Sci., 8, 519 (1952).

31

83. P. Molyneux, in "The Chemistry and Rheology of water Soluble Gums and Colloids (G. Stainsby, Ed. ) Society of Chemical Industry, Monograph No. 24, London (1966).

84. S. Siggia, J. Amer. Pharmaceut. Assoc. Sci., Ed., 46, 201 (1957).

85. A. Kliman, Anesthesiology, 417 (1966). 86. A. Ben - David and S. Gavendo, Cryobiology,_9, 192(1972). 87. E. Glueckauf, Nature, 211, 1227 (1966). 88. S. Sourirajan, "Reverse Osmosis" Logos Press, London

(1970). 89. R.L. Davidson and M. Sittig (Eds), "Water Soluble

resins'-' 2nd ed. , Reinhold, New York (1968). 90. F. Rodriguez and L.A. Goettler, Trans. Soc. Rheol.,

8, 3 (1964). 91. N.G. Gaylord, "Poly ethers. Part I "Polyalkylene Oxides

and other Polymers^ Wiley Interscience, New York(1963). 92. M.M. Breuer and I.D. Robb, Chem. Ind., 530 (1972). 93. I.D. Robb in "Anionic Surfactants, Physical Chemistry

of surfactant action". Edited by E.H. Lucassen Reynders Marcel Dekker, New York, NY. 1981; Surfactant Science Series, Vol. 11, Page 109.

94. I.D. Robb in "Chemistry and technology of water soluble Polymers" Edited by C.A. Finch. Plenum Press, New York NY (1983) P. 193.

95. E.D. Goddard, Colloids. Surf. 255 (1986); 19 , 301(1986).

32

96. I. Satake and J. Yang, Biopolymers 15, 2263 (1976). 97. "Surface phenomena in Enhanced Oil recovery", D.0.Shah,

Ed; Plenum Press, New York, (1981). 98. A. Cahn and J. Lynn,in "Encyclopedia of Technical

Technology", Wiley Interscience, New York, (1983), Page 352.

99. Th. F. Tadros, J. Colloid Interface Sci., 528(1974). 100. K.E. Lewis and C.P. Robinson, J. Colloid Interface Sci.,

539 (1970). 101. M. Nakagaki and Y. Ninomiya, Bull. Chem. Soc. Japan,

817 (1964). 102. S. Saito, T. Taniguchi and K. Kitamura, J. Colloid

Interface Sci., 154 (1971). 103. B.J. Birch, D.E. Clarke, R.S. Lee and J. Oakes, Anal.

Chim. Acta., TO, 417 (1974). 104. M.N. Jones, J. Colloid Interface Sci., 36 (1967) 105. T. Sasaki, K. Kashima, K. Matsuda and H. Suzuki, Bull.

Chem. Soc. Japan, M , 1864 (1980). 106. R. Nagarajan and B. Kalpakei, ACS Polymer Reprints,

March (1982). 107. K. Nakamura, R. Endo and T. Masatani J. Polym. Sci:

Polym. Phys. Ed., 15, 2087 (1977). 108. R. Zana, P. Lianos and J. Lang, J. Phys. Chem., 83,

41 (1985). 109. Frank M. Witte and Jan. B.F.N. Engberts,J. Org. Chem.,

52, 4767 (1987).

33

110. Josephine C. Brackman and Jan B.F.N. Engberts, J. Colloid Interface Sci., 132, 250 (1989).

111. G. Perron, J. Francoeur, J.E. Desnoyers and J.C.T. Kwak,Can. J. Chem. , 990 (1987).

112. Y. Moroi, H. Akisada, M. Saito and R. Matuura,J. Colloid Interface Sci., 233 (1977).

113. K. Shixahama and N. Ede, ibid, 450 (1976). 114. E.A. Lissi and E. Abuin, ibid, 105, 1 (1985). 115. S. Saito and M. Yukawa, ibid, 211 (1969). 116. B. Cabane, J. Phys. Chem., 1639(1977). 117. M.L. Fishman and F.R. Eirich, J. Phys. Chem., 75,

3135 (1971). 118. H. Arai, M. Murata and K. Shinoda.,J. Colloid Interface

Sci. , 223 (1971). 119. M. Murata and H. Arai, ibid, 44, 425 (1973). 120. P.J. Rudd and B.R. Jennings, ibid, 48, 302 (1974). 121. M. Aizawa, T. Komatsu and T. Nakagawa, Bull. Chem. Soc.,

Japan, 3434 (1982). 122. P. Molyneux and H.P. Frank, J. Am. Chem. Soc., 83,

3175 (1961). 123. Gordon. C. Bresheck and W.A. Hargraves, J. Colloid

Interface Sci., 83, 1 (1981). 124. H. Arai and S. Horin, ibid, 372 (1969). 125. M.J. Schwuger, ibid, 43, 491 (1973). 126. F. Tokiwa and K. Tsujii, Bull. Chem. Soc., Japan,

46, 2684 (1973).

34

127. S. Horin and H. Aral, J. Colloid Interface Sci. , 547 (1970).

128. S. Saito, Koll. Z. I M , 19 (1957). 129. S. Saito and K. Kitamura, J. Colloid Interface Sci.,

346 (1971). 130. S. Saito, J. Polym. Sci., A - 18; 263 (1970). 131. S. Harada, K. Komatsu and T. Nakagawa, Rep. Prog.

Polym. Phys. Japan, 19, 17 (1976). 132. T. Isemura and A. Imanishi, Journal of Polym. Sci.,

337 (1958), 133. N.MvuraijS. Makino and S. Sugai, J. Colloid Interface

Sci., 44, 399 (1972). 134. M.L. Smith and N. Nuller, J. Colloid Interface Sci.,

Japan, 769 (1986). 135. H. Maeda, Y. Tanaka and S. Ikeda, Bull. Chem. Soc.,

. Japan, 769 (1986). 136. Paul. L. Dubin and R. Oteri, J. Colloid Interface Sci.,

453 (1983). 137. E.D. Goddard and R.B. Hannan, ibid, 55, 73 (1976).

CHAPTER - I I

COMPETITIVE SOLUBILIZATION OF SUDAN IV

AND ANTHRACENE IN MICELLAR SYSTEMS

36

Hydrophobic molecules which are sparingly soluble in water exhibit enhanced solubility in aqueous micellar solu-tions. This phenomenon known as solubilization is caused by the availability of a non polar microenvironment inside the micelles for the accomodation of the hydrophobic solubli-zates. The incorporation sites of a solubilizate in a micelle are classified into five types according to its chemical nature : (a) in the hydrocarbon core for non polar solubili-zates, e.g., aliphatic hydrocarbons, (b) short penetration into the palisade layer of a micelle by semipolar and polar solu-bilizates e.g., short chain fatty acids and alkanols, (c) deep penetration into the palisade layer by semipolar solubilizates such as napthalene and azobenzene, (d) absorption on the micellar surface by dimethyl pthalate, (e) in the polyoxyethylene shell of the micelle of polyoxyethylene type nonionic surfactants by certain solubilizates such as pinacyanol chloride and chlo-roxylenol. Recent researches on micellar solubilization have

attached attention to locate solubilizates within micelles by (1)

spectroscopic techniques such as Fluorescence quenching,electron (2) (3)

spin echo modulation study, Raman spectroscopy, optically detec-(4,5) (6)

ted magnetic Resonance, ultrasonic spectroscopy, absorption (7)

spectroscopy etc. The solubilization sites which an additive acquires in a micelle greatly depends upon the nature of the additive, its concentration and the micelle type. (6 )

For example, in a recent study it was found that cyclo-hexane is solubilized within the core of the sodium octyl sul-

37

phate micelles, benzene, in the surface for concentrations (8,9)

less than a molecule of benzene per micelle and in the (10)

micellar core at higher concentrations . p-Xylene is reported to be solubilized in the palisade layer for concentrations less than one or two molecules of p-xylene per micelle, for higher concentrations in the core.

A schematic version of various solubilization sites in an aqueous micelle has been shown in figure (3) in chapter-I.

The penetration of solubilizates into the micelles is reported to be accelerated by a number of additives like some

(11) (12-15) (16) alcohols . salts, counterion concentration and pH of the medium.

As has been emphasised previously, the solubilization of hydrocarbons depends upon the nature of the solubilizer,

(17,18) coupled with other factors. Recently many studies have been

(19) undertaken using Laplace pressure technique. Matuura et al have observed that the site of solubilization becomes more hydrophobic with increasing hydrophobicity of surfactants and

(20)

solublizates. Hamidayyah et al have observed the strengthen-ing of hydrophobic bonding and the increase in the degree of micellar ionization by amphiphiles and the micelle - water dis-tribution coefficient as a function of the surfactant chain length in sodium alkyl sulphates.

Of great physiological inportance is the ability of bile salts to solubilize lecithin, cholesterol and other lipidic

38

(21,22) substances. Solubilization of aromatics in aqueous bile

(23,24) salts was carried out by Kolehjnainen.

Recently solubilization in mixed micelles has been (25-27)

the object of study by many workers. The effect of salts on (14,15)

solubilization has been studied by Ikeda et al and several other gl-ou^i?'^^^ An abrupt increase in solublization of Sudan Red B by dodecyltrimethyl ammonium halides at concentra-tion of surfactant and salt corresponding to the sphere-to (30) rod transition was observed. Ueda et al have studied the micellar solubilization of a volatile anaesthetic, Halothane in SDS micelles. Micellar solubilization plays a central role in many analytical applications of systems to shift the position

(31) of an equilibrium reaction to the desired side , enhance the

(32) (33-35) chemiluminescence and fluorescence intensity , allow for

(36) room temperature liquid phosphorescence among others. CO^ETITIVE_SOLUB]arZATrON

When two or more components are present in the solubili-zation experiment, then the phenamenon of preferential solubi-lization of one solubilizate over the other is termed competitive solubilization. Very little work has been done on this aspect of

(37) solubilization. Ruckenstein et al have investigated the solu-bilization of binary mixtures of benzene and hexane in five surfactant systems. The experiments showed that selective solubilization of benzene over hexane occurs in the five surfactant systems investigated. The selectivity ratio for benzene increases with decreasing concentration of benzene in

39

the bulk solubilizate phase which is in equilibrium with the aqueous micellar solutions. Pairs of solubilizates that have widely different solubilization ratios have the largest selec-tivity ratio when solubilized as binary mixtures. Sayeed and

(38,39) Schott investigated the micellar solubilization of lecithin and of mixtures of cholesterol and lecithin by a nonionic sur-factant. They also investigated the solubilization of choles-terol and its binary mixtures with cholesteryl esters of four C^g fatty acids by a nonionic surfactant. The solubilization ratios were independent of unsaturation of fatty acids but decreased with increasing temperature. These studies may offer an explanation that foodstuffs high in polyunsaturated fatty acids cause less atherosclerosis than those containing monounsaturated and saturated fatty acids. Thus the study of competitive solubilization in surfactant solutions may prove as a model from real application point of view in biology, food technology etc. Bile salts, the naturally occuring surface active agents in the body preferentially solubilize particular solubilizates and transport them in the body from one tissue to another.

The present study on the solubilization of Sudan IV and anthracene in micellar systems was prompted due to their reported effects in preventing hydrocarbon induced leukemia in (40) the rats. They were considered non-carcinogenic when admi-nistered in small amounts. PAHs being insoluble in water.

40

are solubilized in the body fluids which generally contain bile salts, proteins and lipids. In fact the body fluid may be considered as an aggregated medium which could solu-bilize various insoluble material. Akin to body fluid a micellar system may be considered as a model system for the study of solubilization of PAHs. Hence a systematic study of solubilization, single and joint, was initiated in aqueous micellar systems. Both types of solubilization studies were carried out in anionic SDS, cationic CTAB and non-ionic TX-100. Free energy of solubilization was also determined both for the singly solubilized and jointly solubilized systems.

41

EXPERIMENTAL

Sodium dodecyl sulphate (SDS) was a product of BDH, Poole (England). It was washed with diethyl ether, recrys-tallized twice from absolute ethanol and dried in vacuo at 80°C. The purity of the surfactant was ascertained from the absence of minimum in the surface tension versus logarithm of concentration plots and therefore was used without further purification. The non-ionic surfactant, polyoxyethylene (9.3) octyl phenol (Triton X~100) was purchased from BDH Chemicals Ltd. Poole,England. It was used as supplied.

The solvents n-hexane, n-octanol and n-decane were BDH-products (99%), n-butanol was E. Merck (India) (99%)

product while n-heptane was obtained from Glaxo (India) Ltd., (99%). They were used without further purification. Sudan IV and anthracene were purchased from Loba-Chemie India and E. Merck (Darmstadt) and were used as supplied. Water was distilled twice in presence of alkaline potassium permanganate in an all quick fit pyrex glass assembly. The specific con-ductivity of water equilibriated with atmospheric carbondio-xide was used through out the work.

[ A ] For the single solubilization experiment, excess amount of solubilizate, Sudan IV or anthracene were added to surfactant solutions of different concentrations and sonica-

42

ted by an ultrasonic processor (RALSONICS), India sonicator for about 15 minutes. The sonicated mass was then shaken for 60 hours in a metabolic shaker maintained at constant tempe-rature, The absorbance of the supernatant liquid was measu-red at an appropriate wavelength of maximum absorption of the solution. After dilution with the surfactant solution of the same concentration, absorbance measurements were carried out on spectronic-20, Bausch and Lomb in the visible region and on VSU-2P, Carl Ziess, Jena spectrophotometer in the ultraviolet region. It was observed that on keeping the solu-bilized systems the absorbance did not change even after keeping the solubilized systems for more than a week. No hydrolysis of SDS is reported to take place during this period.

[ B ] For competitive solubilization experiments, excess amount of approximately equal weights of both the solubiliza-tes Sudan IV and anthracene were added to different surfactant solutions and solubilized in a similar manner (supra vide). After appropriate dilution of the supernatant liquid by the surfactant solution, the absorbance of both the solubilizates at their respective X was measured. ^ max

[ C ] For sequential solubilization experiment, first excess amount of Sudan IV was added to surfactant solutions of diffe-rent concentrations. After shaking the solutions for 60 hours the absorbance of the solutions was measured at X „„„ of

43

Sudan IV after proper dilution as described earlier. After this an excess amount of anthracene was added to each of the surfactant solutions already saturated with Sudan IV. The solutions were once again shaken for another 20 hours at constant temperature. The absorbance of Sudan IV was once again measured at its X . The same procedure was adopted for the sequential solubilization of anthracene followed by Sudan IV. The absorbance in this case was measured at the X of anthracene before and after the addition of Sudan IV. max

44

BESULTS_AND_DISCUSSIONS

The wavelength of maximum absorption, molar absori>-tion coeff icient, IIQ and solubilities of Sudan IV and anthra-cene were determined in the surfactant solutions, water and organic solvents. The of Sudan IV is found to be500nm mo. A and that of anthracene is 252 nm in various solvents and sur-factant solutions and does not change appreciably from solvent to solvent (Fig. 1). Plots of absorbance versus dye concen-tration for Sudan IV are shown in Fig. 2. The E values of Sudan IV and anthracene in different solvents are given in

41 Table-I. The Z value for anthracene was taken as 1.67 x

5 10. Solubility of Sudan IV and anthracene in surfactant solu-tions and organic solvents were also calculated and are given in Table-I.

Absorbance values of Sudan IV and anthracene solubi-lized singly and both jointly in aqueous solutions of CTAB, Triton X-100 and SDS are given in Tables2, 3 & 4 respectively. Plots of absorbance of Sudan IV versus surfactant concentra-tion for single solubilization and both solubilized jointly in CTAB, TX-lOO and SDS are shown in Figures 3-5. Plots of absorbance of anthracene versus surfactant concentration for single solubilization and both solubilized jointly in CTAB, TX-lOO and SDS are given in Figures 6-8. A perusal of figures 3-8 indicates that the absorbance does not change appreciably below the CMC but after the CMC it increases linearly with the concentration of the surfactant. The rapid linear change

45

1. n-hexane 2. n-butanol 3. n-heptan« 4. 0.03M SDS 5. 0.04 M CTAB

SUDAN IV TEMP. 22«C

300 400 500 6 00

FIG. la. SPECTRA OF SUDAN IV IN VARIOUS SOLVENTS AND SURFACTANTS

ffi < (/I

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49

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51

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57

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58

of absorbance after the CMC indicates the phenamenon of micelle formation being similar to phase separation i.e. micelle may be treated as a different phase than the bulk solution of surfactant monomers. This fact could be substan-tiated from the comparison of solubility data of Sudan IV and anthracene in water, organic solvents and aqueous sur-factant solutions (Table-!). The data clearly indicates that the dye solubility in the bulk organic solvent is only an order of magnitude higher than in the micellar solution although values of molar absorption coefficients and do not change appreciably. This is due to the fact that micelles provide favourable non-aqueous environment for the solubili-zate. Moles of surfactant solubilizing a mole of dye, N ^ have been calculated from the slopes of straight lines above the CMC (Figures 3-8) and molar absorption coefficients of Sudan IV and anthracene in the respective surfactant solutions. These values for Sudan LT and anthracene are given in Table-5. Nj is highest for anionic surfactant, SDS and lowest for non-ionic surfactant, TX-100. However, the solubilization of Sudan IV and anthracene in these types of surfactants would also depend on the nature of solubilizates, aggregation number and compactness of the micelle. The values of the aggregation numbers around the CMC in CTAB, TX-100 and SDS have been reported to be 61, 10 and 95 respectively. Thus, Nj values and the aggregation numbers of the micelles would decide the extent of solubilization in these surfactants. It may also be seen from the data in Table-S that for each of the three

59

0 •p ci U ci a o8 M O a o ci H T3 I

«H O CQ < a 0 •H d •H i-l •H ^ iH o to 0) XI •p

H U fl •H

a •H o •o -P O X)

^ X) o a «H cd O CO O

TJ fl d

CO . Q

in M

60

surfactants the value of Nj is found to be much higher for anthracene than for Sudan lY. This indicates that the solu-bility of Sudan IV is higher than anthracene in micellar surfactants, it probably depends on their size and relative polarity, as indicated by their structures.

SUDAN - IV ANTHRACENE

Both the dyes being hydrophobic are probably solubi-lized in different regions of the micellar core. By virtue of its hydroxyl group which can become hydrated, Sudan IV can probably be located in the outermost region of the core, into which some water has penetrated, whereas the more hydrophobic anthracene is probably confined to the innermost anhydrous region of the core. The greater adaptability of Sudan IV would give it an edge during joint solubilization with anthracene, which was found to be true.

The Nj values increase in the joint solubilization for both Sudan IV and anthracene, this increase may be expected because both the dyes compete for solubilization in the same

61

micelle. The more significant fact is that for each of the three surfactants the value of Nj is much higher for anthra-cene than for Sudan IVj indicating a preferential solubili-zation of Sudan IV over anthracene in these surfactants.

the number of molecules of dye solubilized per micelle has been calculated by using the procedure followed by Ikeda et alP*

The solubilizing power, Sg of a surfactant is given as S^ = 1/Np (1)

which gives us the number of moles of dye solubilized in a mole of surfactant. From the value of Sg,£ was calculated where

m' S^ (2)

Where m' is the aggregation number of the surfactant and £ gives us the numberof dye molecules solubilized per micelle. The values of £ for sudan IV and anthracene in both the single and joint solubilization systems are given Table-S". These values indicate that the solubility of anthracene is very much less than that of Sudan IV, which is further reduced in the presence of Sudan IV in the joint solubilization experiment.

Another significant fact can be deduced from the values of Sudan IV and anthracene in CTAB and SDSv It is quite clear that the solubility of Sudan IV and anthracene is more in the

62

cationic CTAB micelles than in anionic SDS. A similar observation was made by Zana et al^^^ and we can explain the difference in behaviour of Sudan IV and anthracene between anionic micelles and quarternary ammonium surfactant micelles in the existence of an affinity of the quarternary ammonium

(42) head groups with aromatic solubilizates, as inferred by others. This affinity would provide an additional driving force for the solubilization process of aromatics by quarternary ammonium surfactant micelles which otherwise is not present with anionic micelles, thereby explaining a larger solubility by the latter / 4 5) than by the former. Maki et ax ' have also reached similar conclusions regarding the increased solubility of napthalene in CTAB than in SDS micelles.

Solubilization ratioP^'^^^ i.e., ratio of N^ of Sudan IV or anthracene in single and joint solubilization processess were calculated for all surfactants. The solubilization ratio of Sudan IV on an average is 1.3 and that of anthracene is 1.2. In a similar work on solubilization of cholesterol with cholesteryl esters of C^g fatty acids in non oxynol 10, Schott

(38 39) and Sayeed ' reported the solubilization ratios close to 1 for cholesterol. We are unable to offer an explanation for our values.

The results on successive solubilization of Sudan IV followed by solubilization of anthracene and successive solu-bilization of anthracene followed by solubilization of Sudan IV

63

are given in Table-6. It can be seen that the absorbance of Sudan IV as well as that of anthracene does not change after the addition of Sudan IV and anthracene respecitvely in all the surfactants, that is, the slope and N^ remain the same. Also, the absorbance of the second solubilizate is quite high. This would mean that the sites of solubili-zation of both components are different and also that once a particular component has occupied its solubilization site the other one is unable to displace it.

The standard free energy of solubilization of dye, AG° in all the three surfactants in different media were calculated using the equation 5. For the following aqueous micellar solution systems the equilibrium for the distribu-tion of a solubilizate between aqueous and micellar phase

(43) can be represented as

s _ aq _ M ox y-s - ^ s ^^s ^ ^ ^

s 3*0 M Where u >a ^ and u are chemical potentials of s s - s the solubilizate in the solid state, aqueous phase and mice-llar phase respectively. The equilibrium (equation 2), asso-ciated with the solubilization of a solid solubilizate is

(44) thus given as :

Solubilizate (aqueous) solubilizate (micelle)...(4)

The standard free energy of transfer of a mole of solubili-zate from the aqueous phase to the micellar phase can be

64 0) 1 A 1 > (V 1 M 0 1

1 D u 1 U D XI 1 T3 e

1 D C! 1 CH TH CO D 1 0 d CO

1 <H M <H 1 Q) Q) o CM o 1 CJ D

1 a Q) D II 1 d O o

D 1 ^ rf •H x jd 1 M ft d

1 o Xi •H Q u 1 CO T ) r<

ti 0 1 XI D T3 d o 1 <3 D d

CO 1 1

0) +J 1 1 B a R] 1 <H B

OJ 1 0 D 0 W 1 ci Q 1 a; O CM

1 o D If) ^ 1 ti <D CM -P x> 1 d o el cj 1 ^ D II d a 1 ^ fH

1 o XI X >>o 1 CQ -p d X 3 0 1 XI D e

RS 1 <3 D r< -O 1 1 0) X ! 1 ^ H 1 0 1 r-i •> 1 RH CQ 1 IH OJ B 0 <5 1 0 -p D

<H H 1 <H tH O 1 O 0 0) o t> 1 o d o M q 1 a > D 0) in •H 1 a M o O

ri ^ 1 X5 D II 1 ^ D +J FN -d M 1 o 'RH X ! 1 CQ TJ +j D

W A I XJ •D D a NJ 1 < d d •<

<H Xl 1 0 3 1 CQ 1 d 1 o >> 1 s •H X> 1 <H s •P 1 0 D eg T ) 1 ISL 0) 1 o o

•H ET 1 O o R-( O 1 C! > LO •H R-H 1 d M X> rH 1 XI 11 ^ 0 1 U D RH SH 1 O d X 0 1 CQ -D d CQ 1 X ! S

1 <! CO 0) 1 > 1

1 CQ 1 CQ 1 0) 1 o 1 o 1 1 CO 1 tH o

o a o o

t> CO CX3 in O CO CD O !M o CO o 00 • • • • • • • • • • • • H CM ro CM m CM CO

00 CM 00 m o 05 CD O CO H CM o 00 • • • • • • • • • • • •

H CO CO CM in CO CO

in CM rH CO CO CD CD m o CO H CM CO m « • # • • * • • • • • • CM CO in tH rH in 1-1 CO rH 00 rH t- a o CO rH

CO CO rH in H CO CO CD 00 in CM O o CM CO in • • • • • • • • • • • • CM CO in H H in rH -CD rH 00 rH t> Ol CJ5 CO rH

m o

o o H in o lo o CM CO lO X

CO p CM (M CO W LO O lO o CO CM CO

I-

65

represented by equation:

A G^ = -RT In (C^ / Cj^) (5) s s s

Where C^ and C * are the concentrations of the solubilizate in unit mole of micellar surfactant and in aqueous phase respecitvely.

o The A G^ values for the solubilization of Sudan IV s

and anthracene and both jointly in CTAB, TX-lOO and SDS are given in Table 5. It can be seen that for each of the sur-factants the value of A G° is more negative for Sudan IV s is more favourable, supporting our earlier inference. The

(44) previous work done in our laboratory on the solubilization of anthracene in ionic micelles with different concentrations o of salts show that A G is independent of ionic strength, O thus it is also independent of aggregation number N since the magnitude of N is known to increase with increasing ionic

(42) strength in the case of ionic micelles. Thus, the con-

o tribution to AG originated from the hydrophobic forces, o

o o o AG and not from the opposing forces A G and A G . Hence

(|) G W

AG° is expected to depend upon the alkyl chain of surfactants, s

66

B-E_F_E_B_LN_C_E_S

1. p. Lianos, M. Viriot and R. Zana, J. Phys. Chem, 1098 (1984).

2. E.S. Pietek, R. Maldonado and L. Kevan, J. Colloid Interface Sci^ 514 (1986).

3. L.B. Shih and R.W. Williams, J. Phys. Chem, 1615 (1986).

4. S. Ghosh, A.H. Maki and M. Petrin, J. Phys. Chem.,90, 5210 (1986).

5. S. Ghosh, A.H. Maki and M. Petrin, J. Phys. Chem.,90, 5206 (1986).

G. D.J. Jobe, V.C. Reinsborough and P.J. White, Can. J. Chem,,60, 279 (1982).

7. M. Gonzalez, J. Vera, E.B. Abuin and E.A. Lissi, J. Colloid Interface Sci, 152 (1984).

8. J.H. Fendler and E.J. Fendler, in "Catalysis in mice-liar and macromolecular systems", Acad Press, New York (1975).

9. P. Mukerjee and J.R.Cardinal, J. Phys. Chem., 82, 1620 (1-978).

10. D.J. Jobe and S.J. Rehfold, J. Phys. Chem., 74, 117 (1970).

11. H. Shirahama and T. Kashiwabara, J. Colloid Interface Sci.,^, 65 (1971).

67

12. K. Shinoda, T. Nakagawa, B. Tamamushi and T. Isemura, "Colloidal surfactants" Acad Press, New York (1963).

13. H. Hiland and E. Vlkingstad, J. Colloid Interface Sci, 126 (1978).

14. S. Ozeki and S. Ikeda, J. Phys., Cham., 89, 5088(1985). 15. T. Imae, A. Abe, Y.Taniguchi and S. Ikeda, J. Colloid

Interface Sci, 109, 567 (1986). 16. A.D. James, B.H. Robinson and N.C. White, J. Colloid

Interface Sci. , 328 (1977). 17. N. Nishikido, K. Abiru and N. Yoshimura, J. Colloid

Interface Sci., 356 (1986). 18. Y. Moroi, and R. Matuura, J. Colloid Interface Sci.,

125, 463 (188). 19. ibid, J. Colloid Interface Sci.,1^, 456 (1988). 20. M. Abu Hamidiyyah, and I.A. Rahman, J. Phys. Chem.,

89, 2377 (1985). 21. D.M. Small, in *'The Bile Acids "(P.P. Nair and

D. Kritchevsky, Eds), p 249. Plenum, New York (1971). 22. N.A. Mazer and M.C. Carey, J. Lipid Res.^^, 932 (1984). 23. E. Kolehmainen and R. Laatikainen, J. Colloid Interface

Sci., 121, 148 (1988). 24. E. Kolehmainen, J. Colloid Interface Sci., 301(1989). 25. C. Treiner, M. Nortz, C. Vantion and F. Puisieux,

J. Colloid Interface Sci., 125, 261 (1988). 26. G.A. Smith, S.D. Christian, E.E. Tucker and J.F. Scamehorn

ibid, 130, 254 (1989).

68

27. Y. Muto, M. Asada, A. Takasawa, K. Esumi and K. Meguro, J. Colloid Interface 632 (1988).

28. F.Z. Mahmoud, W.S. Higazy, S.D. Christian, E.E. Tucker and A.A. Taha, J. Colloid Interface Sci., 131, 96(1989).

29. A.M. Blokhus, H. H0iland, E. Gilje and S. Backlund, J. Colloid Interface Sci., 1 ^ , 125 (1988).

30. T. Yoshida, K. Takahashi, H. Kamaya and I. Ueda, J. Colloid Interface Sci,, 124, 177 (1988).

31. W.L. Hinze, J. Colloid Interface Sci., 5, 425 (1976). 32. W.L. Hinze, T.E. Riehl, H.N. Singh and Y. Baba, Anal

Chem. , 2180 (1984). 33. H.N. Singh and W.L. Hinze, Anal. Lett., 1^, 221 (1982). 34. H.N. Singh and W.L. Hinze, Analyst (London:^ 107, 1073

(1983).

35. D.W. Armstrong, W.L. Hinze, K.H. Bui and H.N. Singh, Anal. Lett. 1659 (1981).

36. L.J. Cline Lene and M. Skrilic, Am. Lab., 103 (1981), Anal. Chem. , 1559 (1980).

37. M.A. Chaiko, R. Nagarajan and E. Ruckenstein, J.Collid Interface Sci,,99, 168 (1984).

38. H. Schott and F.A.A. Sayeed, J. Colloid Interface Sci., 112, 274 (1986).

39. H. Schott and F.A.A, Sayeed, J. Colloid Interface Sci., 112, 144 (1986).

40. C.B. Huggins, N. Ueda and A. Russo, Proc. Natl. Acad. Sci., 75, 4524 (1978).

69

41. K.S. Birdi and J. Steinhardt, J. Biochem. Biophys. Acta, 219 (1978).

42. M. Almgren, F. Grieser and J.K. Thomas, J. Amer. Chem. Soc. , 279 (1979).

43. K.S. Birdi, Colloid Polym. Sci. , 551 (1974). 44. H.N. Singh, K.S. Birdi and S.U. Dalsagar, Indian J.

Chem., 20(A), 595 (1981).

CHAPTER - I L L

INTERACTION BETWEEN A CATIONLC SURFACTANT AND

OPPOSITELY CHARGED DYES

71

Considerable work has been done on the interactions between large organic ions of opposite charge in solution. Some of the most important systems include surfactant-dye, surfactant-polymer and anionic - cationic surfactant mix-tures. Surfactant - dye interactions have implications for drug dosage form design, especially with regard to drug com-

(1-4) patibility, stability and biological availability. These interactions are also of interest in pharmaceutical appli-cations where many formulations contain dyes for colorants and surfactants for preservation, solubilization and stabi-lization purposes and the presence of drugs or other formu-latory adjuvants in the dosage form having opposite electrical (5-7) charge can lead to considerable physicochemical interaction. Surfactant - dye mixtures have also proven useful in several

(8) areas of analytical chemistry including determination of

(9) CMC of surfactants. Anionic cationic surfactant mixtures

(10-12) have been reported to be useful in oil recovery ,

(13-15) (16) cosmetics and also of interest in pharmacy and analyti-

(17-19) (20) cal chemistry as well as waste water treatment , textile

(21) (22-25) w6tting and detergency . Previously , interactions occu-ring in aqueous solution between large monovalent organic ions have been studied using model systems. Ion pair formation, complextion, coacervation and hindered precipitation can all be ascribed to such systems. Thus, information obtained could possibly be used to avoid complexation regions, or to indicate the amount of drug or preservative complexed at any concentra-

72

tion and therefore the amount available for therapeutic or (22)

antimicrobial action. In one of the above investgations it has been reported that the types of possible interactions occuring between large organic ions of opposite charge in aqueous medium depend on factors such as electrostatic and hydrophobic forces, the stoichiometry of these interactions have been determined using conductimetric and turbidimetric methods. The nature and type of interaction products was found to depend on the concentration of the surfactant. At low concentration of surfactant and oppositely charged orga-nic ion, a soluble ion pair formation is reported.At slightly higher concentration of the surfactant an insoluble complex is formed which is finally solubilized in the micelle above

(23) CMC . The effect of various substituents in the benzyl moiety on the interaction between benzyl triphenyl phosphonium chloride (BTPC) and SDS has been investigated by Mukhayer

(26) and Davis at a range of temperatures. Recently a niimber of workers have carried out similar work on the interaction

(28-31) of vitamin B^ with anionic surfactant

In recent years mixed micelles have received a lot of attention. Mixing aqueous solutions of most anionic and cationic surfactants at 1:1 molar ratio produces turbid solutions and eventually precipitation of solids which is a fairly common phenamenon, although in most cases precipitation is undesirable because it renders the surfactant ineffective

73

(32-35) in solution. In most of the work which has been reported on interactions between anionic and cationic surfactants, the authors have reported ion pair formation. Scamehorn

(34) et al have developed a model to predict the precipitation boundary by combining regular solution theory, to calculate monomer micelle equilibrium, with a solubility product relationship between surfactant monomer concentrations to calculate monomer precipipate equilibrium. (4)

Tomlinson and Davis have studied interaction between large organic ions of opposite and unequal charge. The system so investigated is the complexation between oppositely charged unsubstituted and substituted alkylbenzyldimethyl-ammonium chlorides (ABDAC) and bischromones (Sodiiim chromoglycate, SCG) and indigo carmine. The ABDAC-SCG system has been reported to be a model of 2:1 interaction between large organic ions of opposite electrical charge. The results suggest that the electrostatic interactions between the cation and anion charge centers are reinforced or affected by a hydrophobic interaction between suitable moieties of both ions. Also a presence of methylene and chloro groups in the cation molecule leads to a greater tendency of the ABDAC molecule to

(36) interact with SCG. In another work by Tomlinson and Davis , ion association between SCG and a homologous series of ABDACS has been demonstrated at concentrations well below their mutual solubility product values. In aqueous solutions, ion

74

pairs, rather than iontriplets, are predominantly formed between these hydrophobic ions. In the presence of an oil phase, however, it is found that 2:1 ion triplet is formed. Thus, so far, interactions between oppsitely charged organic ions in aqueous solution have been examined by UV

(37) (38) (22 , 28 , 32) spectroscopic , NMR - spectroscopic , conductometric

(39) (40) polarographic and electric dichroism procedures.

The studies involving cationic surfactants with anionic (24,36) (2)

dyes have been far and few . Barry and Russel in the study of amaranth (anionic dye), a pharmaceutical colou-rant and long chain alkyltrimethylammoniumbromides reported the formation of a dye surfactant complex and the solubili-zation of this complex in aqueous surfactant solution. From spectrophotometric studies, they considered the possibility of solubilization of the complex in the palisade layer of the micelles.

In view of the fact that little work has been done on the interaction between cationic surfactants and that too with ions of different valencies, an attempt has been made here to study the interaction between anionic dyes, pyroca-techol violet (PCV) and Alizarin Red S (ARS) with, cetyltrimethylammoiniumbromide (CTAB). .Pyrocatechol violet has been widely used in spectrophotometric investigation of (41) metal complexes and in microdetermination of metal ions Alizarin Red S is used for the determination of concentration

(42) of rare earth metal ions in solution.

75

E ^ E R ^ M T A L

Pyrocatechol violet (Pyrocatecholsulphonpthalein), PCV was purchased from BDH (Poole),England while Alizarin Red S (Alizarin Sodium sulphonate), ARS was E. Merck (India) product. Cetyltrimethylammoniumbromide was purchased from E. Merck (Darmstadt) and was of 'especially pure* grade. All these chemicals were used as supplied. Double distilled water, specific onductivity about 1-2 yohm~^cm~^ was used throughout the work. Conductometric titrations of both dyes with CTAB were carried out on a Philips conductivity bridge model PR 9500 equipped with a dipping type of conductivity cell having platinized electrodes, the cell constant of the two cells used were 0.6 and 0.51 respectively.

For a typical titration 25 ml of PCV (or ARS) solution was placed in a reaction vessel in a constant temperature bath. The conductivity cell was introduced into the solution. After the solution had attained thermal equilibrium a concen-trated solution of CTAB was gradually added in small volumes with a microlitre syringe. The solution was thoroughly mixed and the conductivity of the mixture was noted. Sol vent correcticm was made to the conductivity values by subtracting the con-ductivity of water at that temperature.

In order to determine the iontriplet association constant, a very dilute solution of PCV(or .ARS)was titrated

76

with a very concentrated solution of CTAB, added by means of a microlitre syringe. The conductivity for each addition was measured after thoroughly mixing the solutions. In an exactly similar experiment the conductivity for the addition of dye solution into water was measured. Assuming that the conductance of PCV (or ARS) does not change by very small addition of concentrated solutions, the difference in con-ductivity K was calculated subtracting the conductivity of

sp the PCV ( or ARS ) and CTAB from the total conductivity of the mixture. In order to determine the solubility product of the complex, CTAB was titrated with different initial concentrations of PCV (or ARS) at 30°C. The concentration

- 2

of PCV (or ARS) was plotted against [CTAB] , the concentra-tion of CTAB being the termination of region T. The solubility product of the complex was determined from the slope of this plot.

77

RESULTS_^__DISCUSSION

Typical conductometric titration curves of PCV and ARS with CTAB respectively at a fixed initial concentration of dye are shown in figures 1 and 2 and the corresponding experimental data is given in Tables 1 and 2. A clear region I is obtained for both PCV and ARS at very low con-centrations of CTAB. At slightly higher concentration of surfactant the solution becomes turbid (region II). On further increasing CTAB concentration the turbidity disappears and the solution becomes clear. It can also be observed from figures 1 and 2 that on increasing the initial concen-tration of dye, the concentration CTAB at which turbidity commences is lowered for both PCV and ARS.

Conductometric titrations of PCV and ARS with CTAB were made at different temperatures at a fixed concentration of dye. The specific conductivity concentration data for both PCV and ARS is tabulated in Tables 3 and 4 respectively amd their respective K vs C plots are shown in figures Sand 4.

Region I: In this region the conducting ionic species may be DS03~(dye anions), h" (for PCV), Na" (and h" for ARS), CTA"

— 2 —

and Br . The complex is formed by the interaction of DSO3

and CTA^ ions. The species interaction between the dyes and CTA^ may be represented by the following equation:

DSOg" + xCTA"^=DS03(CTA)J^ (1)

78

t ab le_ i

SPECIFIC CONDUCTIVITY DATA OF PCY AT VARIOUS CONCENTRATIONS OF ADDED CTAB AT 30°C

_ _ _ _

S No CTAB conc^(mM) SxlO^^M PCV 7.5xlO~S PCV 10xl0"Sl PCV

1 0 1.66 2.52 3.24 2 0.04 1.66 2.55 3.33 3 0.08 1.69 2.60 -

4 0.12 1.71 2.63 3.45 5 0.16 1.78 2.70 3.52 6 0.56 2.00 2.75 3.40 7 0.95 2.37 3.15 3.64 8 1.73 2.83 3.52 4.30 9 2.49 2.97 3.92 4.60

10 3.25 3.16 4.22 4.90

11 3.99 3. 36 4.28 5.33 12 5.80 3.97 4.61 5.71 13 7.54 4.25 4.84 6.25 14 10.80 4.72 5.45 6.82 15 • 13.90 5.35 6.00 7.23

16 16.70 6.12 6.52 7.50

17 19.40 6.31 7. 50 8.10

18 21.90 6.97 8.00 8.82

19 24.3 7.69 9.37 10.00

20 26.50 8.10 11.32 11.76

79

SPECIFIC CONDUCTIVITY DATA OF VARIOUS CONCENTRA-TIONS OF ARS AT VARIOUS CONCENTRATION

OF CTAB AT 30°C

s. No.

L

CTAfo conc"(inM) 2xlO~^M

Specific conductivity — 1 —1 4 fi - cm - xlO s. No.

L

CTAfo conc"(inM) 2xlO~^M ARS 4xlO~^M ARS 6xlO~^M ARS

1 0 0.21 0.31 0.56 ' 2 0. 04 0.23 0.42 0.60 3 0.08 0.26 0.44 0.62 4 0.12 0.29 0.45 0. 64 5 0.16 0.34 0.47 0.66 6 0.24 0.45 0.50 0.70 7 0. 32 0.56 0.53 0.72 8 0.40 0.69 0.67 -

9 0.48 0.79 0.78 0.82 10 0.56 0.91 0.93 -

11 0.64 1.02 1.04 1.10 12 0.71 1.09 1.18 -

13 0.79 1.15 1.32 -

14 0.87 1.22 1.47 -

15 0.95 - 1.57 -

16 1.03 - 1.62 1.69 17 1.10 - 1.77 18 1.18 - - 1.85 19 1.26 - - 1.94 20 1.34 2.02

80

in D O I -o >

Ci) u c to t/5

a

CD < o U) D tn L. cs

o > CO u D •c C

c > f J

8 ^ o o u a CO

•J o a

lL

c .2 • •w C C u c o u

( (JUD XT) OL X /^^lAjpnpuoo onloads L ~ L ~

81

( jxio IT) OLX X^jAUDnpuoo Oj^pads I i " *7

82 TABLE__3

SPECIFIC CONDUCTIVITY DATA OF CTAB IN PRESENCE OF 5xlO~^M PCV AT VARIOUS TEMPERATURES

1 s . CTAB Specific conductivity — 1 - 1 4 fi-^cm xlO^ No. conc"(mM) 30°C 35°C 40°C

r •• 1 0 1.66 1.72 1.85 2 0.04 1.66 1.79 1.90 3 0. 08 1.69 1.83 2.00 4 0.12 1.71 1.90 2.05 5 0.16 1.78 1.92 2.07 6 0.56 2.00 2.22 2.47 7 0.95 2.37 2.48 2.86 8 1. 73 2.83 3.15 3.50 9 2.50 2.97 3.46 4.00 10 3.25 3.15 3.75 4.90 11 3.99 3.36 4.00 4.90 12 5.80 3.97 4.30 5.20 13 7.54 4.25 4,60 6.12 14 10.80 4.72 5.40 7.23 15 13.90 5.35 6.25 8.00 16 16.70 6.12 6.66 -

17 19.40 6.31 - 10.00 18 21.90 6.97 - 11.76 19 24.30 7.69 - -

20 26.50 8.10 - -

J

83

TABLE 4

SPECIFIC CONDUCTIVITY DATA OF VARIOUS CONCENTRATIONS OF CTAB IN PRESENCE OF 2xlO"^M ARS AT VARIOUS TEMP.

s . No.

CTAB conc'^(mM)

Specific^ 30°C

conduct lvitj7 35®C

_sr_cm~_xlO_ 40°C

— ^ —

1 0 0.21 0.22 0.24 2 0.04 0.23 0.25 0.28 3 0.08 0.26 0.27 0.32 4 0.12 0.29 0.30 0.36 5 0.16 0,34 0.34 0.48 6 0.24 0.45 0.46 0.72 7 0.32 0.56 0.59 0.75 8 0.40 0.69 0.72 0.88 9 0.48 0.79 0.83 1.00 10 0.56 0.91 0.94 1.10 11 0.64 1.02 1.05 1.19 12 0. 71 1.09 1.11 1.26 13 0.79 1.15 1.19 1.35 14 0.87 1.22 1.25 1.41

84

O OM

O c CP L. a

•D Ci) •O TD O n CD <

CD < h-O O -r-c g o

•*->

c o u c o u

K- cn o G) LJ L. LJ D • 0 t_ CT l_ a > £ C9

-»-> *-> — > C •W Ci o ( -D C9 "D C o b o •4-> o u

> "u o Q. a in O £

ID o

o H-a o

cn

il

( ujo IT) OL X AjiAijonpuoo D^ioads L- I-

85

O

CD <r h-o o c o ••J o u c Ci) o c o u

w o c Ci> U) C9 i_ a c

"D •o •D 0 r-1 CD < H- U) O G 1 1 L. 3 U) -«-•

D O U) i_ Cii a > E Ci > >

> c u 3 6) 13 «»-C o •D u u 0

C/5 o cr C9 a < Cfl s o E

CM 0) O o

> » -Q. o

vt

iZ

( UJO -IT) OL y /<ji/vuonpuoo o u p a d s L- L - V

86

2 + Where DSOg" and CTA represent the anion of PCV or ARS and cation of CTAB respectively.

In order to determine the value of x, very dilute equimolar solutions of PCY (or ARS) and CTAB were prepared. Three sets of solutions of pure dye, pure surfactant and dye surfactant were prepared by mixing the respective solu-tions in various proportions as indicated in figures 5 and 6 tabulated in tables 5 and 6. The specific conductivity versus mole fraction plots for pure CTAB and pure dye were linear. When no reaction takes place between DSO^" anion and CTA"* cation the specific conductivity of their mixture must be on the straight line BD, obtained by adding the specific conductivities of pure dye in water and only sur-factant in water at a particular mole fraction. However, the conductance of their mixtures are decreased (figures 5, 6, curve BOD) which is due to the formation of a non conduc-ting species. A plot of the specific conductivity of the mixture versus surfactant mole fraction indicates a minimum at 2:1 surfactant dye ratio. The formation of a 2:1 complex between surfactant and dye is verified by plotting [dye] vs

— 2

[CTAB] which must yield a straight line passing through the origin. Such a plot is shown in figure 7. This proves that the insoluble complex is indeed formed in a 2:1 r a t i o .

The mean values of solubility product, K derived from the s 3 slopes of these curves were found to be 6.4 p mol

87

TABLE_^5

SPECIFIC CONDUCTIVITY DATA OF PCV, CTAB AND PCY - CTAB IN WATER AT VARIOUS TEMPERATURES

^S. CTAB No.

conc xlO^M

PCV n conc

xlo' M

Specific conductivity x lO^n-^cm"^

30°C 30°C 40°C

1 0 0 0.17 0.33 0.39 2 0.16 0 0.57 0.88 0. 96 3 0.32 0 0.92 1.04 1.47 4 0.48 0 1.37 1.59 2.14 5 0.64 0 1.79 1.98 2.64 6 0.80 0 1.92 2.30 3.15 7 0 0.80 2.68 3.09 3.44

8 0 0.64 2.17 2.56 2.83

9 0 0.48 1.70 2. 10 2.31

10 0 0.32 1.17 1.27 1.39

11 0 0.16 0.65 0.83 1.03 12 0 0 0.17 0.33 0.39 13 0 0.80 2.68 3.09 3.44 14 0.16 0.64 2.36 2.83 2.64

15 0.32 0.48 2.14 2.50 2.83

16 0.48 0.32 1.95 2.28 2.74 17 0.64 0,16 1.88 2.26 2.94

18 0.80 0 1.70 2.30 3.18

88

M L E _ _ 6

SPECIFIC ' CONDUCTIVITY DATA OF VARIOUS CONCENTRATIONS OF CTAB, ARS AND ARS - CTAB IN WATER AT DIFFERENT

TEMPERATURES

r S. No.

t.

CTAB^ conc xlO'^(M)

ARS conc' xlO^(M)

Specific

30°C

conductivity

30°C 40°C

1 0 0 0.10 0.14 0.17 2 0.06 0 0.40 0.44 0.47 3 0.12 0 0.65 0.74 0.87 4 0.18 0 0.87 1.04 0.17 5 0.24 0 1.20 1.34 1.52 6 0.30 0 1.47 1.62 1.88 7 • 0 0.30 1.31 1.46 1.70

8 0 0.24 1.04 1.20 1.39 9 0 0.18 0,86 0.94 1.09 10 0 0.12 0.60 0.68 0.79 11 0 0.06 0.34 0.39 0.48 12 0 0 0.10 0.14 0.17 13 0 0.30 1.31 1.46 1.70 14 0.06 0.24 1.26 1.42 1.62

15 0.12 1.18 1.24 1.39 1.58

16 0.18 0.12 1.23 1.39 1.57

17 0.24 0.06 1.35 1.50 1.71

18 0.30 0 1.47 1.62 1.88

89

CO < M H >s U T) O

o §

p o

o o 2 2

E

CQ < H-<J

I

> U ol L. o tf) * *

o a c o u o

>»-

Ml o E lA 3 (A i. •

ft) u > e O st > X3 C U o 3 X> u e c tn o <n o

*

u o • • o < • » o o <n ft) a * * 0

d>

( (juo XT) ot X ^ J i A i j o n p u o o oi^pads L" L- 9

( ujo V ) Oi X ^;!MionpuoD oi^ioads L~ 9

91

TABLE__7

DATA FOR THE [ DYE ] VERSUS [ CTAB AND LOG [ CTAB VERSUS LOG [DYE] PLOTS AT 30°C

[CTAB] xlO^M

[PCV] xlO^M

[CTAB]"^ xlO-® M-2

Log[CTAB Log[PCVr

r 1.2 0.50 0.69 -7.84 -3.30 1.0 ' 0.75 1.00 -8.00 -3.15 0.8 1.00 1.56 -8.19 -3.00

I

[ARS] [ [CTAB] 1 xlO^M

[ARS] xlO^M

[CTAB]"^ xlO"® M"^

Log[CTAB]^ Log[ARS]

T— ~

1 1.20 0.2 0.69 -7.84 -3.69 I 0.75 0.4 1.77 -8.20 -3.39 j 0.60 0.6 2.77 -8.44 -3.22

92

CM

CD <t I— O U J

cn o

1<25

o 1-00 E

fo O ^ 0-75 K

tt 0-50 > o LJ

0-25

0-00

- 8 - 6

- 8 ' 4

- 8 - 2

- 8 - 0

- 7 ' 8

- 7 ' 6

C CTAB3"^X 10"®(lfr/mo( )

J. X

• P C V

• A R S

©

- 2 7 - 2-9 - 3 - 1 - 3 - 3 - 3 - 5 - 3 - 7

log Cdye]

- 2 0 (a) CdyeJ versus C C T a B A at 30 C

2 0 (b) t o g C C T A B ] versus Log CdyeJ at 30 c

Fig. 7

93

—9 3 —9 dm and 2.34 p mol dm for PCV and ARS respectively. Double logarithmic plots of the concentrations of each ion at the breakpoint for both dye - CTAB systems were construc-ted and are shown In Figure 7. Both dyes exhibited this

2 Straight line relationship between log [CTAB] and log [dye], showing that over the concentration range studied the areas of ion self association have been avoided. Regression ana-lysis of these double logarithmic plots gave slopes approxi-mately equal to 1. This indicates a 2:1 interaction between the monovalent cations and divalent anions.

0 i U O H or c — ( O ) ~ 0 H rriT

0 l l ^ ^ S O o N a

^ S 0 3 H

Pyrocateohol Violet Alizarin Red S

Taking the configuration of PCV and ARS in view the formation of 1:2 dye surfactant complex may be suggested by the structure and polarity of the two dyes. Out of the two surfactant molecules, one of the surfactant molecules may be associated with the sulphonate group of PCV whereas the other can attach to the phenolic group adjacent to the quinoid group on the other hand in ARS,one surfactant molecule may be attached with the sulphonate group whereas the other may

94

perhaps be attached to the phenolic group adjacent to the quinoid group due to steric reasons.

In another study of ARS - CTAB interaction by Malik (37)

et al , it was indicated that the binding is favoured in both neutral and alkaline medium than acidic medium due to favoured ionization of phenolic as well as of sulphonate groups providing two negative centres in the dye molecule for two positively charged monovalent CTA"* ions to interact. Since both the dyes obey Beer Lambert law therefore the possibility of any self association of dye molecules can be safely ruled out in the concentration range studied. Also the support for this comes from the linear double logarith-mic plots for both the dyes. Hence the ion - triplet inter-action may be written as

DSO3" (aq) + 2CTA' (aq) DSO3 (CTA)2 (s) (2) The ion triplet association constant may be written

^DS03(CTA)2 - ^lontripl.t — Xj,s03 (""cTA)

Where Kienti'iplet is the association constant and X represents the concentration of the respective species. At

— 4 -3 an initial concentration of PCV, 5 x 10 mol dm and ARS, 2 X 10"' mol dm~^ and varying concentration of CTAB the con-centration of the complex was calculated by a method analo-grous to Job's method of continuous variation applied to ion - pair equilibrii^^"^^' The basic assumption is

95

that conductivity is strictly a linear function of the con-centration of electrolytes.

With this assimption the specific conductivity of CTAB in water, K^T^g can be expressed by the equation:

^CTAB * ^ ^CTAB^ (4)

Where A^T^g is the equivalent conductivity and C is —3 the concentration of CTAB in moldm

Assiiming further that the degree of dimerization of CTAB, PCV and ARS is 0 as stated earlier,(both dyes obey Bee» Lambert law), then the value of specific conductivity of the mixed system CTAB + PCV and CTAB + ARS can be consi-dered as a linear function of the concentration of various species in dilute solution and may be given by equation:

K^jXlQ? = ^PCV or ARS^' + ^CTAB^ (5)

Where Ap^^ equivalent conductivity of PCV or ARS and C is its concentration. Since the total quantity of PCV or ARS in the titration vessel remains cons-tant during titration, the difference in the specific conduc-tivity of the mixture and that for CTAB alone in water can be due to the dilution of PCV or ARS by CTAB solution and the possible formation of nonconducting iontriplet PCV (CTAB)2 or ARS (CTAB)2. Hence the specific conductivity of the mixture may be given by the equation;

96

AK„ X 10- = Ap^^ (C. - X.) + A^^^g (C - 2x.) + x. + m SXgj.- ) (6a)

for PCV - CTAB interaction and,

\ - = ÂRS - ' i) Actab ^ -i ^

^ K r - )

for ARS - CTAB interaction, where x^ is the concentration of nonconducting c o m p l e x a r i d Xg^ are the limiting

conductance of H"*", Na*" , Br" respectively, and these values at experimental temperatures were estimated from the litera-ture valuel'^^\ Assuming that the theoretical deviation from the observed conductivity is due to the formation of a complex, the conductivity change can be determined by subtracting equa-tions (6) from (5). The conductivity change (^K^) due to

3

iontriplet formation is then AK^ x 10 = ^p^y + ^^CTAB'î

— x. + ) (7a) for PCV - CTAB interaction and

'^m lo' = % R S 'î + X, - x, ^ X^^^ ^ 2X°^_)(7b)

for ARS - CTAB interaction. Using equations (7) the concentra-tion of the iontriplet x ^ is obtained as

A K X 1 0 ^ x^ = m - ^ K r - >

97

for PCV - CTAB interaction and AK X 10^

X = IS ( 8b )

for ARS - CTAB interaction, where AK is the difference in m conductivity between the mixed system and completely ionized CTAB solution containing an amount of completely ionized PCV or ARS. These values are tabulated in Tables 8 and 9 for PCV and ARS respectively. No appreciable change in Ap^^ or A ^ g was found by small addition of very concentrated solution of surfactant hence its value was taken as constant at a given temperature. The iontriplet association constant for both dyes, PCV and ARS, calculated from equations (3) and (8) are given in Tables 10 and 11. From the value of , the standard free energy of iontriplet formation, AG° was determined using equation (9). The value of enthalpy, AH° was calculated from the temperature dependence of ^iontriplet (equation 10). A linear regression program was used to fit the data: (ordinatettemperature, abscissa:ln ^iontriplet^'

AG° = -RT in AH° = Rt2 -HT in K.^^triplet

It may be seen from figure 3 that the formation of PCV (CTAB)2 complex commences at a lower concentration of surfactant when the temperature is increased. This indicates that the reaction is endothermic. This fact is supported by

98

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102

the positive enthalpy values, AH° for the reaction shown in Table 10. On the other hand, for ARS - CTAB system, complex-ation commences at a higher concentration of CTAB with increase in temperature. This is supported by the fact that the AH° values are negative (Table ID indicating that the reaction is exothermic.

It may be seen from the results in Table 8 that the enthalpy of complex formation is positive for PCV - CTAB interaction (Pigure 3). This shows that an increase in temperature of the system favours the complex formation. The increased entropy values and decreased aG° values also support the statement.The reason for this can be attributed to the effect of temperature on the biak dielectric constant of water. The reduced dielectric constant at higher temperature leads to an enhanced ionic interaction and a reduced hydrophobic interaction. Mukhayer and Davis have observed a similar behaviour in the interaction of BTPC and SDS at a range of temperatures.

A reverse phenamenon has been observed for the ARS -CTAB system. From Table 11 it can be seen that the enthalpy of complex formation is negative for ARS - CTAB interaction. A similar type of behaviour has been reported by Hashizume et al^^^^ between Alkyl pyridinium chlorides and sodium alkyl sulphates. It can also be seen that AS° is positive but decreases with increasing temperature and AG° increases with

103

increasing temperature. It is quite evident that ARS - CTAB interaction is favourable at lower temperatures.

Diamonc " ^ had postulated the presence of ionpairs in water, such that for large organic ions in water, there is a tightening of the surrounding water 'structure' and that if two ions of opposite charge are present and both are large and hydrophobic in character, then the hydrogen bonded water structure forces them together to maximize the water - water interactions and to minimize the disturbance to itself. The production of this 'Water - structure enforced' ion pairing involves both electrostatic and hydrophobic interactions, the relative contribution of which is dependent upon both ions' structures and their immediate environment.

Region II The onset of turbidity in the solutions and a change in the slope of the conductivity curve can be described as the start of formation of an insoluble complex leading to the separation of an insoluble phase and the ions in the solution as a solid or separate phase. The solubility product of both the complexes has been calculated before to be 6.4

3 —9 3 —9 pmol dm and 2.34 p mol dm . For a 2:1 complex plots of 2

[dye] versus [CTAB] were linear and pass through the origin (Figure 7) from which the solubility product was calculated. The disappearance of turbidity marks the end of this region. Region III This region is characterized by the termination of region II and disappearance of turbidity after addition

104

of excess amount of surfactant. Another interesting feature of this region is that there is a change in the gradient of conductivity versus concentration of titrant plots (Fig.1,2) indicated by an arrow between region II and III. The dis-appearance of turbidity at higher concentration of CTAB can be regarded as the consequence of solubilization of the complex.

105

R E F E R E N C E S

1. E. Tomlinson, S.S. Davis and G.I. Mukhayer, in "Solution Chemistry of SurfactantiS" (K.L. Mittal, Ed), Vol. 1, p. 3, Plenum Press, New York, 1979.

2. B.W. Barry and Q.F.J. Russel, J. Pharra. Sci., 61, 502 (1972).

3. D. Attwood and A.T. Florence, "Surfactant Systems", P.388, Chapman and Hall, New York, 1983.

4. E. Tomlinson and S.S. Davis, J. Colloid Interf. Sci., 66, 335 (1978).

5. P.H. Elworthy, A.T. Florence and C.B. MacFarlane, in "Solubilization by surface Active Agents and its Appli-cations in Chemistry and Biological Sciences", pp. 11, 217, Chapman and Hall, Suffolk, 1968.

6. G. Schuster and H.K. Modde, Amer. Perfum. Cosmet., 86, 37 (1971).

7. H. Nogami, J. Hasegawa and M. Iwatsuru, Chem. Pharm. Bull. , 2297 (1970).

8. M.E. Diaz. Garcia and A. Sanz - Medel, Talanta, 255 (1986).

9. P. Mukerjee and K.J. Mysels, J. Amer. Chem. Soc. , 77, 2937 (1955).

106

10. R. Nagarajan and M.P. Harold in "Solution behaviour of surfactants" (K.L. Mittal ed.) Vol. 2, p 1391, Plenum, New York, 1980.

11-. J. Sabbadin, J. Le Moigne and J. Francois in "Surfac-tants inSoLution" (K.L. Mittal, ed.) Vol. 2, P.1377, Plenum New York, 1984.

12. D.O. Shah and R.D. Walker, in "Research on Surfactant Polymer Oil Recovery systems",University of Florida, 1980 Annual Report for U.S. DOE Contract No. DE . AC 1979 BC 10075.

13. Great Britain Patent 2, 122, 898 (1984) [Chemical Abstr., 101, 12011W].

14. Japan Patent 59, 187, 095 (1984) [Chem. Abstr., 102, 190833U].

15. Japan Patent 60115, 511 (1985) [Chem. Abstr., 103,22Q601g], 16. B.K. Sadhukhan and D.K. Chattoraj., in "Surfactants in

Solution" (K.L. Mittal Ed.) Vol. 2 p. 1249, Plenum, New York, 1984.

17. B.J. Birich and R.N. Crockroft, lon-sel. Electrode Rev., 3, 1 (1981).

18. W. Lin, M. Tang, J.J. Stranahan and S.N. Deming, Anal. Chem., 1872 (1983).

19. R.V. Scowen and J. Leja, Can. J. Chem., 45, 2821(1967). 20. U.S.S.R. Patent 1, 028, 605 (1983) [Chem. Abstr., 100,

12l44w].

107

21. M.J. Schwuger, Kolloid Z., 243, 129 (1971). 22. G.I. Mukhayer and S.S. Davis, J. Colloid Interface

Sci. , 224 (1975). 23. ibid, ibid, 350 (1976). 24. ibid, ibid, 350 (1977). 25. ibid, ibid, 65, 210 (1978). 26. ibid, ibid, 582 (1977). 27. ibid, ibid, 110 (1978). 28. S. Singh, S. Kumar and H.N. Singh, J. Surf. Sci. Tech.,

2(2), 115 (1986). 29. H.N. Singh, S. Singh and 0. Singh, Prog. Colloid and

Polymer Sci., 63, 112 (1978). 30. M. Abe, M. Ohsato, T. Kawamura and K. Ogino, J.Colloid

Interface Sci., 228 (1985). 31. Y. Nemoto and H. Funahashi, ibid, 95(1977). 32. M. Mitsuishi and M. Hashizume, Bull. Chem. Soc., Jpn.,

46, 1946 (1973). 33. L. Sepulveda and J. Perez - Cotapos, J. Colloid

Interface Sci., 21 (1986). 34. K.L. Stellner, J.C. Amante, J.F. Scamehorn and J.H.

Harwell, ibid, 186 (1988). 35. A. Mehreteab and F.J. Loprest, ibid, 125, 603 (1988). 36. E. Tomlinson and S.S. Davis, ibid, 74, 349 (1980). 37. W.U.Malik and S.P. Verma, J. Phys. Chem., 70, 26(1966). 38. R.P.Taylor and r.D. Kunz, J. Amer.Chem. Soc., 92,

4813(1970).

108

39. S. Hayaao, K. Kageyama and T. Suzuki, Kagyo Kagaku Zashi, 126(1965).

40. A. Yamaglshi, J. Colloid Interf. Sci., S6, 468(1982). 41. A. Yamagishi, J. Phys. Chem. , 2129 (1981). 42. Ju. Lurie, "Hand Book of Analytical Chemistry", English

translation, Mir Publications, Moscow, 1975. 43. CRC Hand Book of Chemistry and Physic^s, Ed. R.C. Weast,

CRC Press, Florida, 1978. 44. R.M. Diamond, J. Phys. Chem., 67 , 2513 (1963).

CHAPTER - LV

INTERACTION OF POLYVINYL PYRROLIDONE WITH

TRIETHANOLAMINE DODECYL SULPHATE

110

The properties of non-ionic water soluble polymers such as PEO, (polyethyleneoxide), PVP (polyvinyl pyrrolidone) and PVA (polyvinyl alcohol) are of interest in view of their use as industrial stabilizing agents, and also because of their use as biological model systems for ligand binding to

(1 2)

complex structures such as drug receptor sites ' . In additio,n these polymers may mimic proteins when studied by methods commonly used for protein characterization. For example the formation of hydrophobic domains, or clusters associated with the binding of surfactants below their CMC to proteins^^^ can also be demonstrated for PVP^^\as obser-ved by the enhanced solubility of water - insoluble dye upon adding surfactant to polymer containing solutions.

Generally it is found that the binding of ionic surfac-tants by polyions of opposite charge starts at concentrations as much as two orders of magnitude lower that the CMC of the surfactant. On the other hand in case of non-ionic polymers, binding of ionic surfactants occurs close to the CMC. Two transition points can be clearly observed in plots of surface tension, conductivity and dialysis versus surfactant concen-

( 4-9) tration in the presence of polymer . The state of sur-factant in the presence of polymer can be considered as follows, when the concentration of surfactant increases, the adsorption of surfactant on polymer (complex formation)begins at the first transition point which does not change much with the amount of polymer. Between the first and second transitition points, the added concentration of surfactant is

Ill

mostly, consumed by complex formation with polymer and the concentration of singly dispersing ions of surfactant in-creases slightly with the increase in the amount of surfac-tant whereas micelle formation does not occur. After the saturation adsorption of surfactant on polymer has been attained at the second transition point, micelle formation can occur.

Based upon the above observations models have been proposed for the nature of the aggregates formed. Recent

(10,11) spectroscopic studies have provided a physical picture of this process. The portion of the structure involving the surfactant resembles a mixed micelle as also suggested

(12,13) . from indirect evidence which may account for the CMC

(14,15) (16) reducing action of the polymers . Zana et al have studied the interaction between SDS and POE (and PVP) by a

(17) recently developed fluorescence method . The main conclu-sions of this study were that (i) polymer - surfactant inter-actions mostly occur at the micelle surface and very strongly depend on the nature of the surfactant head group and that (ii) the SDS micelles bound to polymer are smaller than the micelles formed in the absence of polymer : the larger the polymer concentration the smaller the micelle aggregation number.

Several workers have studied polymer surfactant inter-(4, 18-21)

action at various polymer conceatrat ions . Jones has

112

studied the interaction of polyethylene oxide with sodium dodecyl sulphate. The range over which the surface tension remains constant depends on the concentration of the polymer. At low polymer concentrations the plateau is short since the total number of binding sites is relatively small. At higher polymer concentrations the surface tension remains constant over a greater range. Also absorption of surfactant on high concentrations of polymer commences at a lower con-

(19) (21) centration of surfactant . Engberts et al have calcu-lated a, defined as the ratio of the slope in the second region of the conductivity plot to that in the first region in the study of SDS with PEO and PPO. The larger value of a for the complexed micelles is indicative of an increased degree of ionic dissociation as a result of interactions with the polymer. At still higher concentrations of SDS (Beyond second transition point) only unperturbed SDS micelles are formed as supported by the magnitude of a, which is equal to that of SDS solutions in the absence of polymer. Also, the concentration range between T , and Tg increases with increa-sing polymer concentration.

Several authors have studied polymer surfactant inter-(22-29) (23)

action using viscometric techniques . Saito et al observed the strengthening of the interactions of dodecyl ammoniumions with PVP, PEO and PVA-Ac by changing the con-terion from chloride to thiocyanate. Whereas the specific

113

viscosity of a PVP solutioa changes little by addition of dodecylammonium chloride, addition of dodecyl ammonium thio-cyanate (DASCN) decreased it at low concentrations and raised it remarkably at high concentrations. This behaviour has been attributed to a concurrent binding of the dodecylammonium ion with SCN~ to the hydrophobic parts of the polymers. The

( 25 viscosity changes found by Lewis and Robinson for SDS-PVA have been interpreted as a result of two effects, viz., binding of the DS~ ion to the polymer chain and changes in the state of aggregation of the polymer in solution as influenced by the binding process and the ionic strength of the solution. The effect of salts of hydrophobic organic counter ions with (26 27) nonionic polymers was studied by Saito et al ' and

(28,29) others '

The effect of added salt on the interaction between PVP ( 30 31

and PVAc with SDS has been studied by Arai et al^ ' and (32 )

others using the techniques of surface tension, viscosity and solubilization. They found that reduced viscosity was reduced by the addition of Nad.

(31) Arai et al calculated the heat of complex formation of SDS with PVP (AH ) in NaCl solution from the temperature ^ (8,18,33,34)

dependence of the first transition point. Several studies on the temperature dependence of polymer surfactant interaction have shown that processes which are affected by hydrophobic

114

interactions are temperature dependent. Increase of tempe-rature was found to reduce the chance of complex formation • between polymer and surfactant. Engberts et al^®^ have calculated the free energy of stabilization of the micelle by polymer complexation and these values indicate that the interaction between micelles and polymers is quite dependent on the structural charge.

An increase in the surfactant alkyl chain length has the effect of enhancing polymer micelle interaction.

(4,32,33,35,36) Comparable effects have been reported in the past

A plot of log of concentration at first transition point versus hydrocarbon chain length was found to be linear.

Complex formation is strongly dependent upon the length of the polymer chain. With increasing molecular weight of the polymer chains, the tendency towards complex formation strongly increases. Noteworthy, however, is the fact that above a given molecular weight of the polymer the niimber of monomer units in the molecule has no further influence on the complex formation. Several authors have studied the polymer surfac-

(34,37-38) tant interaction in relation to degree of polymerization The research work concerning interaction of surfactants with polymers leading to formation of surfactant polymer complexes is of great value for industrial formulations of certain health care and cleansing products. In such formulations mono, di-and triethanolamine type of surfactants are widely used.

115

Triethanolaminedodecyl sulphate (TDS) is an important constituent in cosmetic products like shampoos. Moreover, since its CMC (4mM) is lower than that of SDS (8.3 mM)at 25°C TDS proves to be a better surfactant. In addition, its foa-ming power is nearly equal to the foaming power shown by

/•QQ 40'i aqueous SDS at its CMC^ ' \ Hence it was thought worth-while to study the interaction of triethanolamine dodecyl sulphate with a more popular and widely used polymer, PVP. Viscometric and conductometric techniques have been used to study the TDS - PVP system in aqueous solution. The effect of polymer concentration, temperature, ionic strength and molecular weight on the interaction has been initiated.

116

EXPERIMENTAL

Triethanol amine lauryl sulphate (TSD) was synthesised by the,following procedure:

Thirty Seven grams of lauryl alcohol distilled at 142-144/15 mm Hg was sulphated in hexane with 33 gm of pure sul-phonic acid at O.C over a period of 4 hours. After the com-pletion of the reaction, the product was poured dropwise into

f

200 cc of 10% aqueous triethanolamine solution with stirring at a temperature below 5°C. The whole material was then shaken twice with petroleum ether to remove unreacted alcohol. The water portion was dried over the hot water bath and finally in a vacuum dessicator. The product was recrystallized repeatedly from ethyl acetate or ethanol. The absence of minima in the log surface tension vs concentration of surfac-tant indicated a pure surfactant. The CMC of the surfactant TDS, so prepared was found to be 1.51 wt% (3.9 mM) which is in

(39) close agreement with the reported literature value of 1.66 wt/o (4 mM).

Polyvinyl pyrrolidone, PVP (K - 90) was purchased from Fluka chemie AG (Switzerland). It was used without further purification, other polymers used were PVP (K-15), PVP (K-25) and PVP (K-30) which were also procured from the same source. Sodium chloride was an E. Merck (India) product.

117

Ordinary distilled water was first demineralized by an Ion exchange column. It was distilled twice in presence of alkaline pottasiumpermangnate in an all quick fit pyrex glass assembly. The specific conductivity of water was about 2 X 10" ohm" cm" . Water equilibriated with atmos-pheric carbondioxide was used throughout the work.

(b) Pregaration_of_solutionsi For viscosity studies stock solutions of TDS, below, near and above its CMC were prepared in distilled water. These solutions were used to prepare PVP (K-90) polymer solutions. Thus the surfactant concentration was kept fixed and polymer concentration varied for a particular set of experiment.

For conductivity measurements, stock solutions of PVP (K-90) of 0, 0.1, 0.3, 0.5, 0.7 and 0.9% concentration were prepared in distilled water. These polymer solutions were used as a solvent to prepare TDS solutions. Thus, for con-ductometric study polymer concentration was kept constant and the surfactant concentration varied for each set of experiments.

(c) Viscosity Measurements! The viscosity measurements of solutions were carried out in an ubbelohde viscometer, ther-mostated in a constant temperature bath maintained at 30°C. The relative viscosity (n .) of solutions was calculated from the following relation -

_ t

118

Where, n and n^ are the viscosities of solution and solvent respectively, t and t^ are the flow time for a fixed volume of solution and water respectively at the experimen-tal temperature. Other viscosity parameters can be related as

^sp = % - 1

= n c red. P

Where n is the specific viscosity, c is the poly-sp p mer concentration and is the reduced viscosity. Density corrections were not made since these were found to be negligible.

(d) Measurement_of_Electrical_Con

The electrical conductance of solutions was measured by a Phillips conductivity meter model PR 9500, equipped with platinized electrodes (cell constant = 0.51 cm~^).

119

RES^TS_Aro_DrSCUSSM

(a)

The viscosity parameters such as relative viscosity n^ and reduced viscosity n^^^ were calculated for (T. 1%, 0.287, and 0.425 TDS solutions in presence of different con-centrations of PVP (K-90) and are tabulated in Table-l.The reduced viscosity plots for TDS solution in the presence of different concentrations of PVP (K-90) are shown in figure 1.

Figure 1, for TDS - PVP system clearly shows that the reduced viscisty (n^^^) increases abruptly at low polymer concentrations with decreasing concentrations of polymer. Also as the surfactant concentrations decrease the rapid increase in becomes less intense. The reduced viscosity plot of PVP solutions with respect to TDS concentration at various, concentrations of PVP were found to be linear (see figure 2). The slopes of these straight lines decrease with increasing concentration of PVP. This behaviour is consistant

/ 22 •) with the findings of Isemura et al for PVF in SDS and Sodiiam Laurate systems. A similar behaviour was observed by

(25 ) Lewis and Robinson for PVA - SDS system. From our residts it may be supposed that the polymer/surfactant complex behaves as a typical polyelectrolyte. The kind of viscosity behaviour exhibited by our system may be explained by two effects viz.,

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121

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0-2 0-4 0-6 0-8 1 0

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122

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Fig. 2 Variation of reduced vitcofity with IDS concentration at various concen trations of PVP ( K - 9 0 ) at 30®C .

123

binding of the DS~ ions to the polymer chain and changes in the state of aggregation of the polymer in solution as influenced by the binding process and the ionic strength

C 22) of the solution. According to Isemura et al the rapid increase in ^ g j .t low polymer concentration is due to an anamolous viscosity behaviour arising from adsorption of polymer molecules by the capillary wall of the viscome-

f 41 42) ter ' , but since this effect is absent in absence of surfactant ions and the increase in is dependent on surfactant concentration we may explain the increase in ^red ^^ polymer concentration in terms of the appearance of the first electroviscous effect (i.e., deformation of the double layer around the polyelectrolyte chain under shear). Another factor responsible for the abrupt increase in is the swelling of the polymer coil as a result of acquired charge. This swelling reflects an increase in the intrinsic viscosity of the polymer on the addition of surfactants. (b) Conductivit2_nieasurements: Conductivity data at various concentration of PVP (K-90) is given in Table-II. Plots of specific conductance as a function of TDS concen-tration are shown in figure 3. From these plots it may be seen that the specific conductance varies linearly with increasing TDS concentration upto the first break at a well defined TDS concentration (T ), below the CMC of pure TDS.

124

TABLE__2

SPECIFIC CONDUCTANCE OF VARIOUS CONCENTRATIONS OF TDS IN PRE-SENCE OF DIFFERENT CONCENTRATIONS OF PVP (K-90) AT 30°C.

S. No.

TDS conc' Specific conductance x cm"^)

0.1% PVP 0.3% PVP 0.5% PVP 0.7% PVP 0.9% PVP

1 0 0.30 0.30 0.30 0.20 0.11 2 0.017 0.57 0.65 0.62 0.47 0.48 3 0.035 0.85 0.91 0.98 0.88 0.81 4 0.052 1.19 1.18 1.19 1.22 1.00 5 0.070 1.48 1.51 1.57 1.60 1.40 6

• 0.087 1.82 1. 81 1.91 1.85 1.70

.7 0.105 2.14 2.15 2.19 2.15 1.91 8 0.140 2. 78 2. 72 2.71 2.78 2.42 9 0.175 3.40 3.34 3.29 3.26 2.89 10 0.210 3.77 3.89 3.98 3.61 3.35 11 0.245 4.35 4.35 4.43 4.15 3.83 12 0.280 4.76 4.81 4.95 4.51 4.25 13 0.315 5.25 5.42 5.42 5.15 4.72 14 0.350 5.67 5.66 5.93 4.98 5.10 15 0.385 6.07 6.22 6.31 5.26 5. 54

16 0.420 6.54 6.71 6.89 5.81 6.07

17 0.455 6. 98 7.08 7.18 6.21 '6.53

18 0.490 7.38 7.50 7.50 7.50 6.98

19 0.525 7.74 7.84 8.09 7.28

125

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After T^, K deviates from linearity and follows a curve which ultimately approaches a second straight line.

Below the first transition point T^, no interaction between the polymer and surfactant can be detected. The specific conductance changes in the manner expected in the absence of the polymer. At the first transition, the curvature in the plot indicates that the docecyl sulphate ions are adsorbed onto the polymer. The presence of the polymer has been reported to alter the water structure sufficiently to promote free DS' ions to "vacate" the solu-tion and binding onto the polymer seems to be the favoured process. As a consequence of binding the conductance initially decreases relative to that of DS~ ions in the absence of polymer and probably also because of binding of T^ ions result-ing from the high charge density in the region of polyanion. At the second transition the polymer is saturated with the DS~ ions and beyond T^ micellization around the polymer and in the solution may occur. The range of TDS concentrations between T^ and T^ depends on the concentration of the polymer. At low polymer concentrations, this region is short. With an increase in polymer concentration T^ more or less remains unchanged while T^ increase, thus reflecting an increasing interaction of surfactant and polymer at higher concentration of polymer.

127

If the number of adsorption sites increases linearly with polymer concentration the second transition should in-crease in the same way and extrapolate to the CMC of TDS at zero polymer concentration. Such a plot is shown in Fig.4. The data gives a least squares line with slope (0.7) and intercept 0.1755 . Thus extrapolation of T^ to zero PVP concentration gives the CMC of TDS i.e. 0.175% which is in close agreement with the calculated value of 0.166%. Also, the concentration o"f TDS consumed in the formation of poly-mer-surfactant aggregates i.e. T2 - CMC is plotted against the concentration of PVP in solution in Fig. 4. It can be seen that the composition of polymer - surfactant aggregates is constant i.e., ratio of PVP and TDS is 2.5:1 regardless of the concentration of PVP in solution.

a, is defined as the ratio of the slope in the second region of the conductivity plot to that in the first region upto T^. The larger value of a for the complexed micelles is indicative of an increased degree of ionic dissciation as a result of interactions with the The value of a for PVP - TDS system comesout to be 0.84. We also observe a curvature in the region between T^ and Tg. Witte and

C 7) Engberts have suggested that the curvature is caused by an increase of the aggregation number and/or gradual uncoil-ing of polymer both with increasing concentration of TDS.

128

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0 •49

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Fig. 4 Eff«ct of PVP ( K - 90 ) on TDS at th« sccond transition and th« concantration of TDS contumcd in tht formation of polymer surfactant complex at 30 ®c •

129

(11) The effect of temperature on the specific conductivity of 0.5% PVP (K-90) in presence of ImM NaCl at various concen-trations of TDS has been studied and the data is tabulated in Table III. The plot of specific conductance of 0.5? PVP (K-90) in ImM NaCl versus TDS concentration at different temperatures is shown in figure 5. It can be seen that there is a slight increase in the conductance with increasing temperature. T^ and T^ also increase with increasing tempera-ture. This indicates that hydrophobic forces are dominating the process because processes which are affected by hydrophobic interaction are temperature dependent. Hence complex formation between polymers and surfactants can be made much smaller by increasing the temperature as is reflected by increase in T^.

The effect of temperature on the CMC, concentration of TDS at first and second transition concentration, and ~ in presence of 0.55 PVP in ImM NaCl is shown in figure (6a).

(31 •) The heat of micellization (AH^) for an ionic sur-

factant is represented by the equation: ^ i n ^ p . R T ^ i i ^ A ! ^ . Kg ^1)

Where R is the gas constant; T, absolute temperature, P, the pressure; Kg an experimental constant and C^ ig ^^e concentration of counterion. C^ is the concentration of salt plus the CMC in the present experiments. Since the CMC is

130

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Concentration of I D S (w / v V . )

Fig. 5 Th« cffcct of tcmptroturc on tht specific conductivity versus concentration of TDS in Irr^M NaCl solution in the absence and presence of 0 ' 5 w t V « P V P . T ft T2 are tlie concentrations at the first and second transition points respectively

1. TOS at 25'C 3- TDS at 30*C 5. TDS at 35*C 7. TDS at «0®C

2. PVJ» - TDS at 25'C A. PVt» - TDS at 30 ' C «. PVF» - TDS at 35'C 8. PVP _ TOS at AO'C

The curves b, c and d hav* been shifted upwords by 1,2 and 3 scole units ( 1 X I c m " ! ) respectively

132

more or less constant and so is the salt concentration,

equation (1) can be written as:

= -RT^ ( In CMC/ T) (2) m p

The concentration of TDS at the first transition point of PVP - TDS (T^) was lower than the CMC of TDS at each temperature. C^ is constant in the complex formation of TDS with PVP. The heat of complex formation of TDS with PVP, (AHc) in ImM NaCl can be expressed by the equation:

AH^ = -RT^ ( In T.y T) (3) c 1 p

The values of CMC, In CMC, T^ and InT^ at different temperatures are tabulated in Table 4.

TABLE_4

VARIATION OF CMC OF TDS AND T^ AT DIFFERENT TEMPERATURES IN THE PRESENCE OF 0.5% PVP IN

ImM NaCl.

s. No.

Temp. °(C)

CMC (%) of TDS

In CMC T^ (X) In T^

r - -1 25 0.136 -1.991 0.042 -3.17 2 30 0.140 -1.966 0.052 -2.95

3 35 0.144 -1.937 0. 063 -2.76

4 40 0.147 -1.917 0.077 -2.56 1

133

The values of In CMC and In T^, are plotted in figure (6b). These plots are straight lines with a corre-lation coefficient of (0.9999) and (0.9978) respectively. From the slopes of these plots in Figure (6b), the values of AH^ and AH^ at different temperatures were calculated and are given'in Table 5.

TABLE__5

THE HEAT OP MICELLIZATION (AH ) OF TDS IN ImM NaCl m SOLUTION AND THE HEAT OF COMPLEX FORMATION AH OF c TDS WITH 0.5% PVP ( K - 90 ) in ImM NaCl.

s. No.

Temp.(C) m (Cal/mol)

AH^ (Kcal/mol)

1 25 -844.0 -7.2 2 30 -872.5 -7.4 3 35 -901.6 -7.7 4 40 -931.1 -7.9

It may be seen from table 5 that both AH and AH m c decrease with increasing temperature. The negative values show that both the processes are exothermic in nature.

For the ionic micelles a reduction of the CMC is taken as the evidence for micelle polymer interaction. In a first approximation, the Gibbs free energy of stabilization of the micelle by polymer complexation is given by i

134

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(T ) AG . . - AG . = RT In — (4) mic-pol mic

Where T^ is the concentration of surfactant at the first transition and CMC the corresponding critical micellar concentration value for the unperturbed micelle. The values of free energy denote the change in free energy when 1 mole of surfactant molecule is transferred from normal to polymer bound micelles plus the change in free energy of the polymer induced by this process. Table 6 lists the variation of T^, In (T^/CMC) and AG with temperature.

TABLE__6

VARIATION OF T^, In (T^^^j^^) and AG WITH TEMPERATURE

c c Z L i e r '

1 25 0.136 -0.07 -96.5 2 30 0.140 -0.06 -84.0 3 35 0.143 -0.05 -71.0 4 40 0.147 -0.04 -63.2

Thus it can be seen from Table 6 that polymer - sur-factant complexation is more favourable at lower temperatures in the range investigated. Several important temperature dependent studies with the related systems have been reported

(8,28,33,34) in the literature

136

(34) As meationed earlier, Witte and Engberts calculated the value of a for SDS - PEO and SDS - PPO systems. From figure 5 the values of a have been calculated and they come out to be 0.77,0.75 and 0.64 at 30°C, 35°C and 40°C respecti-vely. The larger value of a at lower temperature is indicative of an increased degree of ionic dissociation as a result of interactions with the polymer. Thus, the values of a also support the evidence from AG calculations that polymer sur-factant Interaction is more favourable at lower temperatures.

(iii) The effect of molecular weight of the polymer on specific conductivity vs concentration of TDS in 0.5% PVP is given in Table 7. The plot of specific conductivity versus concentration of TDS in 0.5 weight % PVP of different mole-cular weights is shown in figure^ 7. It can be seen from figure 7 that the specific conductivity decreases with the increase in molecular weight of the polymer. This behaviour may be explained on the basis of the fact that the number of DS~ ions adsorbed on the polymer surface depends upon the size of the polymer leading to a more depletion of DS~ ions from the solution for complex formation with a heavier poly-mer, which is reflected in a decrease in conductivity. It can also be seen from figure 7 that although T^ more or less remains constant, Tg increases with increase in molecular weight of the polymer and becomes constant beyond PVP (K-30). This trend is more in accordance with the fact that there is

137

TABLE__7

SPECIFIC CONDUCTANCE OF DIFFERENT CONCENTRATIONS OF TDS IN PRESENCE OF 0.5?: PVP OF DIFFERENT MOLECULAR WEIGHTS

1 s. TDS 1 1 Specific conductance X 10 ( a ^cm ^ ) No. conc"(%) 1 1 1 K - 15 K - 25 K - 30 K - 90

1 0 0.70 0.39 0.25 0.05 2 0.017 1.07 0.73 0.62 0.41 3 0.035 1.44 1.08 0.98 0.75 4 0.052 1.69 1.32 1.20 1.20 5 0.070 2.00 1.65 1.55 1.35 6 0.087 2. 46 2.06 1.88 1.75 7 0.105 2. 72 2.35 2.17 2.00 8 0.140 3.31 2.96 2.74 2.50 9 0.175 3.83 3.69 3.33 3.15 10 0.210 4.32 4.18 3.85 3.60 ll 0.245 4.90 4.60 4.32 4.15 12 • 0.280 5.31 5.15 4.76 4.60

13 0.315 5.70 5.54 5.20 5.05

14 0.350 6.15 5.90 5.65 5.55 15 0.385 6.45 6.30 6.05 6.01 16 0.420 6.88 6.75 6.50 6.39

17 0. 455 7.28 7.10 7.00 6.85

18 0.490 7. 95 7.90 7.75 7.60

19 0.525 7.96 7.90 7.75 7.60

138

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139

an increase In the interaction of polymer and surfactant (34)

with increasing molecular weight of the polymer. Shwuger has studied the interaction of SDS with PEG series and has inferred that with increasing molecular weight of PEG the tendency towards complex formation strongly increases.

(8 ) Brackman and Engberts have also observed no change in polymer micelle interaction on varying the molecular wight of PEO from 10,000 to 20,000.

From figure 7, the constant value of T^ for PVP (K-30) and PVP (K-90) indicates that the interaction initially depends upon the molecular weight of the polymer and after reaching an optimum molecular weight the interaction becomes independent of molecular weight of polymer. (iv) The effect of added NaCl on the interaction of PVP-TDS interaction is shown in figure 8 and the data is tabulated in Table 8. It can be clearly seen that increasing the concentra-tion of NaCl, the first and second transition concentration of TDS as well as the CMC decrease. This behaviour seems a typical case of salt induced surfactant polymer interaction.

(31) Similar behaviour was also reported by Murata and Arai

Thus on the basis of the above set of experiments we can say that the, TDS - PVP interaction would be partly chemical and partly physical in nature. It appears that in this context electrical interaction is significant, too. The nitrogen atom in the pyrrolidone ring with its lone electron

140

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pair could possibly become slightly positively charged, which would favour an adsorption of the negatively charged surfactant ion. This effect would be enhanced by the hydro-phobic interaction between the hydrophobic part of the surfactant and the hydrophobic sections of PVP. With

(43 44^ cationic surfactants ' the difference is that there would be a repulsion between the positively charged cationic surfactant and the pyrrolidone nitrogen atom. In this case, not only there would be no electrical attraction, but, as a consequence there would be a weakening of the hydrophobic bonding between the hydrophobic sections of the two species.

143

1. p. Molyneux, in "Wateri A comprehensive Treatise" (F. Franks, ed.), Tol. 4, p 569 Plenum Press, New York, 1975.

2. P. Molyneux, in "The chemisti?? : and Rheology of water soluble Gums and Colloids" (G. Stainsby,ed.)

p 91, Society of Chemical Industry:, Monograph No. 24, London, 1966.

3. J. Steinhardt, M. Stocker, D. Carroll and K.S.Birdi, Biochemistry, 4461 (1974).

4. H. Arai, M. Murata and K. Shinoda, J. Colloid Inter-face Sci., 223 (1971).

5. I.M. Klotz and K. Shikama, Arch. Biochem. Biophys., 128, 551 (1968).

6. T. Sasaki, K. Kashima, K. Matsuda an.d H. Suzuki, Bull. Chem. Soc., Japan, M , 1864 (1980).

7. Frank M. Witte and J.B.F.N. Engberts, J. Org. Chem., 4767 (1987)

8. J.C. Brackman and J.B.F.N. Enberts, J. Colloid Inter-face Sci. , 250 (1989).

9. E.A. Lissi and E. Abuin, ibid, 105. 1 (1985). 10. B. Cabane, J. Phys. Chem., 11, 1639 (1977). 11. B. Cabane, and R. Duplessix, in "International Symposium

on solution behaviour of surfactants - Theoretical and applied Aspects"

144

12. H. Arai, M. Murata and K. Shinoda, Journal of Colloid Interface Sci., 223 (1971).

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