are completely miscible with water (viz. methanol and ethanol)does not cause any substantial increase in the specific conduc-tance of the surfactant solutions. The increase in specific conduc-tance of the solution is discussed in terms of factors affecting theperturbation of the double layer of the micelle.

INDIAN J. CHEM., VOL. 20A, MARCH 1981

Cis-fA)

trans-fA)

benzene ring. Thus the lateral molecular separationin Series-A is less compared to biphenyl monoanils.Hence, the commencement of smectic phase is obser-ved, though. late.

The authors are thankful to Prof. J. S. Dave forhelpful discussion. One of us (N.N.T.) is thankfulto the UGC, New Delhi for a junior research fellow-ship.

References1. GRAY, G. W., Molecular structure and properties of liquid

crystals (Academic Press, London), 1962, 282.2. FERGASON,J. L., TAYLOR,T. R. & ARORA, S. L., J. org.

Chem., 35 (1970), 4055.3. FERGASON,J. L., ARORA, S. L. & SAUPE,A., Mol. Cryst.

Liq. Cryst., 10 (1970), 243.4. YOUNG, W. R., HALLERI. & GREEN,D.C., J. org. Chem.,

37 (1972), 3707.5. GARDLUND,Z. G., CURTIS, R. J. & SMITH,G. W., Liquid

crystals and ordered fluids, Vol. 2, edited by J. F. Johnsonand R. S. Porter (Plenum Press, New York), 1974, 541.

6. VORA, R. A. & GUPTA, R. Paper presented at the AnnualConvention 0/ Chemists, Kurukshetra, 1979, abstract No.ORG-81.

7. DAVE, J. S. & KURIAN, G., Mol. Cryst. Liq. Cryst., 42(1977), 175.

8. DAVE, J. S. & KURIAN,G., J. Phys., C1 (1975),403.

Effect of Some Organic Additives on the Conductivityof Aqueous Micellar Solutions

H. N. SINGH*, SHANTISWARUP,R. P. SINGH& S. M. SALEEMDepartment of Chemistry, Aligarh Muslim University,

Aligarh 202 001 .

Received 13 February 1980; revised and accepted 26 June 1980

The effect of polar and nonpolar organic compounds on thestability of micelles of ionic surfactants, viz, sodium dodecylsulphate and cetyltrlmethylammonium bromide has been studiedconductometrically. It has been found that the addition of polaradditives, viz. n-butanol, n-pentanol, n-hexanol, m-cresol andaniline, which have only limited solubilities in water, increasesspecific conductance. The specific conductance attains a maximumvalue and with further addition of polar additives, it decreasesrapidly and the surfactant solutions become gradually turbid.The addition of nonpolar compounds which are miscible withwater (viz. n-hexane and toluene) and also polar compounds which

292

I

THE effects of the presence of additives on thecritical micelle concentration of surfactants

have been widely studied>", Micellar solutionsare seldom used as such, but rather as emulsionsor microemulsions which may find application inthe enhanced recovery of oil in future+". Micro-emulsions are generally quaternary systems com-prising H20, surfactant, cosurfactant and oil. Re-cently, it has been reported that the stability of micro-emulsions may result from their dynamic characterenhanced by the presence of cosurfactants (C, toCe alcohols". Addition of small amounts of ali-phatic alcohols to a concentrated surfactant solutionhas been found to increase the conductivity of thesolution in the beginning but it falls off rapidly, athigher alcohol concentrations. This typical behaviourof only one type of additives (alcohols) has beenexplained as due to preferential partitioning ofalcohols (depending on their chain-length) resultingin the change of micellar interface. However, asystematic attempt has not been made to study theeffect of organic additives of varying polarities on themicelles of different structures and compactness. Wereport here the results of our studies on the ternarysystem comprising ionic surfactant, organic additiveand water.

Sodium dodecyl sulphate (SDS) and cetyltrimethylammonium bromide (CTAB) were BDH and SigmaChemical Co. reagents and these were purified asdescribed earlier".

All the additives used in the present study wereeither BDH or E. Merck products. These werepurified by distillation before use. Doubly distilledwater of conductivity I X 10-6 ohm"! cm-1 wasused throughout the work. Conductivity measure-ments were made using a Phillips conductivity meter,model PR 9500, as described elsewhere=",

It is well known that micelles of increasinglygreatersize and compactness are formed when concentrationof the surfactant in solution is gradually increasedbeyond critical micelle concentration (CMC). Suchtransitions for SDS and CTAB are shown in Fig. 1.These transitions indicate that micelles that existin aqueous solution at a particular concentration ofsurfactant, are fairly narrowly dispersed in size-".Therefore, it can be reasonably assumed that insurfactant solution of concentration correspondingto the region slightly above the transition points(Fig. I), micelles of only one particular type arepredominantly present.

The additives that have been studied are of thetypes, (a) aliphatic nonpolar, (b) aromatic nonpolar,(c) aliphatic polar, and (d) aromatic polar compounds.The concentrations of the surfactants in which theeffect of the above organic additives has been studiedwere so chosen that they were fairly higher than the

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NOTES

CTAB

e (b)

6

~

"ie 2\I

Ie.c 00 0 '0 20 30 ~o~~x 50S~ 60 (0)

~o

°o~---~~o----e~O~~'~2~O--~~~0--~2~O~O~~2~~~O~C(mmol/litrel

1 - Plots of specific conductivity (K) vs concentrations(m mol/litre) of surfactants ,in water at 25°C.

Fig.

TA,BLB1 - PERCENTAGE(v/v) OF ORGANICADDITIVESREQUIREDTOSHOWMAXIMUMIN THESPECIF!CCONDUCTIVITYOFMICELIAR

SOLUTIONSOF SURFAcrANTSAT 25°C

Cone. of n-Pro- n-But- n-Pen- n-Hex- n-Hep- m-ete- Ani-, surfactant panol anol tanol anal tanol sol line(m mol/litre)

Surfactant = SDS

200 15.0 13.0 5.0 4.0 1.0 4.0 5.5150 12.5 11.5 4.0 3.0 0.6 3.5 5.0120 11.0 10.0 3.5 2.5 3.5 4.580 10.0 8.8 3.0 2.0 3.0 4.210 9.0 8.0 2.0 1.0 2.0 3.5

Surfactant =CTAB

50 15.8-25 12.5 4.8 1.5 0.8 2.5 4.030 14.0---22 11.0 3.5 1.0 0.2 2.0 3.520 13.0---20 10.0 3.2 1.0 1.8 3.010 12.0---18 8.0 3.0 0.8 1.0 2.51 6.0 4.0 2.0 0.3 1.4

concentration corresponding to the first CMC ofsurfactants (Fig. 1). Thus the effect of the additiveson the SDS solution of concentrations 10, 80, 120,150 and 200 m mol/litre and CTAB concentrations1, 10, 20, 30 and 50 m mol/litre have been studiedand the results are summarized in Table 1.

Whereas nonpolar water immiscible compounds,viz. n-hexane and toluene and completely watermiscible polar compounds, viz. methanol and ethanoldo not cause any increase in the specificconductivity,the addition of polar compounds which are partiallymiscible with water, viz. aliphatic alcohols of chainlength varying from C3 to C7 and also aniline andof m-cresol cause a sharp increase in the conductance

I

'00 505(200 mmol/litrelom-Cresol6 Aniline• n- Pentonol)( n- Hexanol• n- Heptanol6 n- Butanol• n- Propanola Merhanolb Erhano,c Toluened n -Hexane

A

20( )

20( )

20( )

o ~--~----~----~----~--~o 5 W ~ ~ ~'/, of Organic Additives (v/v I

Fig. 2A- Variation of K of SDS with increased % oforganic additives at 25°C.

20 CTAB(SOmmol/Iit,e! o..

10

m-CT'eso'Anilin •

n-pentonoln- Heoxanoln- Butonoln- Proponol

•1S

"V ''" ~5(x)

25A

•20 \

u"ies:

15 'l~

)(

l£

5

5(4L __ ~----"~:,:- __ -:2fO__ --=;15;:-__ ..:;10=-__ ..:;.5__ --",O 2'5o 5 10 15

y, of Orgon',e Additives (v/v)

Fig. 2 B - Variation of k of CT AB with increased % oforganic additives at 25°C.

aqueous solutions of both the surfactants (Fig.2A,B).With the gradual addition of the additive, the con-ductivity reaches a maximum value and then beginsto fall off rapidly. It is known that the major factorthat determines the inter-micellar solubility of long-chain alcohols is the change in hydrophilic balanceof the micelle during the inclusion of alcohol in itll.An increase in the conductance of the surfactantsolutions can come about through three possiblefactors : (i) increase in the number of free counterions due to adsorption of additive molecules in thelayers, (ii) increase in the number of free surfactant

293

INDIAN J. CHEM., VOL. 20A, MARCH 1981

3. HAYARE,K. & HAYANO,S., Bull. chem, soc. Japan, 50(1977), 83.

4. SHAH. D. O. & SCHECHTER.R. S .• Improved oil recovery bysurfactant & polymer flooding (Academic Press. N.Y.).1977.

5. COOKE. C. E .• Jr .• Microemulsion oil recovery process,of the counter ions from the micelles) and partly U. S. Patent. (1965). 373. 809.due to the release of a few surfactant ions from the __ 6. REISBERG.J .• Surfactants for oil recovery by water-floods,micelles. But as the chain-length of alcohol increases" U. S. Patent. (1965). 348.upto five carbon atoms, the increase in the specific 7. SKOULIOS& GUILLON.D .• Phy s. lett .. 38 (1977). L-137.conductivity is caused entirely by the released counter 8. SINGH. H. N. & SWARUP. S .• Bull. chem. Soc .• Japan. 51ions. Though the additive may cause a change in (1978). 1534.the shape and size of the micelles, it seems unlikely, 9. SINGH. H. N:. SWARUP. S. & SALEEM,S. M., J. Colloidespecially in concentrated solutions of surfactants Interface SCI.. 68 (1979). 128. . .where micelles have high aggregation numbers that 10. SHINODA. K.• Solvent properties of surfactant solutions

. . .' (Marcel Dokker , New York), 1967; Jungerman,micelles of much different shapes will be formed. E. Cationic surfactants (Marcel Dekker New York) 1967.Therefore, increase in the mobility of the micelles 11. RA~STON. A. W. & EGGENBERGER.D. W.. J. Am. ·chem.cannot be considered as a significant factor in accoun- Soc .• 70 (1948). 983.ting far such a sharp increase in the conductivity 12. LAWRENCE.A. S. C. & PEARSON.J. P .• Trans. Faraday Soc.,of the solution, When the alcohol content is at 63 (1967). 495.a certain level, hydrophobization of micelle as aconsequence of the appearance an its surface ofalcohol hydroxyl groups, which are less polar thanionic groups of the surfactant, leads to' pronouncedturbidity of the solution. The turbidity is inducedby the separation of a mesomorphic phase consistingof surfactant-alcohol and water.

As mentioned above, the contribution of mana-meric surfactant ion to' the observed increase inconductivity decreases with increasing chain-length.With n-pcntanol the increase is entirely due to' thereleased counter-ions, thus the lower heights of maximaobserved in the cases of n-hexanal and n-heptanalmay partially be due to' the lack of any contributionof conductivity by the monomeric ions, Comparingthe effectiveness of m-cresal and aniline with thoseof alcohols, it seems that the former additives liebetween n-pentana) and n-hexanal (Table 1). It is,therefore, obvious that the nature of the polar groupsand size of nonpolar moiety bath together determinethe effectiveness of these compounds,

It may be interesting to' mention that n-actanallldoes not give rise to' any maximum in conductance.The higher alcohols being completely insoluble inwater will completely solubilize in the micelle interiorand therefore will not cause any perturbation in theelectrical double layer where the counterions areheld. Octanol, tho ugh having a polar-Off group,behaves exactly as the completely non-polar saluteslike n-hexane and toluene. It will, however, beinteresting to' see what effect iso-actanal will havesince the -OH group in the molecule occupies amiddle position in the chain. Further work withcompounds containing multiple groups and branchedchain structures is being carried out in our labora-tory,

The authors are grateful to' Prof, W. Rahamanfar providing facilities. Thanks are also due to' theCSIR, New Delhi far providing financial assistanceto'S. S. and R. P. S.

ions, and (iii) increased mobility of charged units.Lawrence and Pearson-", using Na+ ion selectiveeletrodes, have found that increase in the conducti-vity of 2 % aqueous solutions of SDS is due to' thepresence of alcohola (essentially because of the release

References1. MALIK.W. U., VERMA.s. P. & CHAND.P .• Indian J Chem.,

8 (1970), 826.2. NISHIKIDO.N .• MOROI. Y .. VEHARA.H. & MATuuRA. R.,

Bull. chem. Soc. Japan, 47 (1974). 2634.

294

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(

Standard Rate Constant of Sb(III)jSb(Hg) Exchangein Alkaline Medium

M. M. ABOU-RoMIADepartment of Chemistry. Faculty of Science. Cairo University,

Cairo, Giza, Egypt

Received 17 March 1980; revised and accepted 16 May 1980

Apparent standard rate constant values (kg) for the reductionSb(III)/Sb(Hg) in 1M NaOH and KOH have been determinedusing faradaic impedence measurements. From the values of thereaction rate constants at different temperatures in 1M NaOH,it is concluded that the reduction is irreversible under the experi-mental conditions used. The enthalpy of activation 6.Ht hasbeen calculated from the slope of the linear plot between kg andlIT.

STUDIES using oscillographic polarography showedthat the reduction of tervalent antimony was

irreversible in the presence of certain base elec-trolytes-. This conclusion was also confirmed byNorakidze et af.2. The rate constant values for thereduction of Sb(III) in acid solutions were alsoreported", In this note are reported the apparentstandard rate constant values (k.) of Sb(III)jSb(Hg)exchange in 1 M NaOH and KOH. The techniqueemployed is essentially polarography with super-imposed alternating voltage.

The capacitative and resistive components of themercury surface were measured on an a.c. bridgesimilar to that used by Grahame+, The bridge,polarization cell and d.c. polarizing circuit wereessentially the same as described previously". In thepresence of tervalent antimony and with no current-maxima suppressor added, the pseudocapacity andover-all polarization resistance were traced over anappropriate potential range at a normal workingfrequency of lOOO Hz. The effect of a higher fre-quency i.e. 3000 Hz on the peak em and Rm valueswas also studied. The results were analysed vecto-rially to determine the components of the impedance

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