ABSTRACT

The present Ph.D. thesis comprises six chapters viz;

Introduction, Synthesis of Compounds and Their Analysis (IR

Spectroscopy, CHNS, XRD, FE-SEM), Thermogravimetric Analysis,

Differential Thermal Analysis and Differential Thermogravimetry,

Electrochemical Analysis (Conductivity and Effect of Additives) and

Acoustical (Ultrasonic) Studies. Appendix includes- Abstract, Future

Scope and List of Publications.

The chapter-1 deals with the general introduction of Surface

Chemistry and Surfactants. Alkaline earth metal stearates are classified as

anionic surfactants. The present investigation is initiated considering the

significance of this vast field to the important domains like

Pharmaceuticals Science, Chemistry and Bio-Chemistry. The section on

introduction however proceeds with relevant references. At the end of the

introduction section a precise account of the present work is mentioned

emphasizing the significance of the present study.

The chapter-2 deals with Synthesis of Compounds and Their

Analysis (IR Spectroscopy, CHNS, XRD, FE-SEM). The techniques

employed in industry for the preparation of anionic surfactants (specially

metal carboxylates) can be classified as precipitation and fusion method.

The respective stearates of magnesium, calcium, strontium and

barium were prepared by direct metathesis. The aqueous solution

containing stoichiometric amount of respective metal carbonate and

potassium stearate were mixed at about 80°C under constant stirring. As

evolution of CO2 ceased and metathetic displacement reaction completed

(phenolphthalein indicator rendered colourless from pink), the desired

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compound was separated from mother liquor by vacuum filtration. The

product was washed several times with benzene and then oven dried. All

the four compounds thus prepared were further purified by

recrystallisation from methanol-chloroform solvent mixture. The white

coloured pure and well dried compounds were then stored over calcium

chloride. The recrystallized pure compounds are found to decompose

between 190-205°C. The structure of the purified products was

ascertained using physicochemical techniques like elemental analysis

(CHNS), infrared spectroscopy, XRD and FE-SEM. The percentage

CHNS data (both experimental and theoretical) is found to support the

proposed structural formulae of alkaline earth metal stearates.

Infrared spectra were obtained with KBr and CsI pellets. The

spectra were also recorded with Nujol and Fluorolube mulls. These

spectra showed practically no differences from the pellet spectra. All

infrared spectra were recorded on a BOMEM DA3-02 Fourier transform

spectrometer equipped with high-speed vector processor, and a PDP11-

03 computer for data processing. A germanium coated KBr beam splitter

and a high sensitivity, liquid nitrogen cooled mercury cadmium telluride

detector were used for the 3500-500 cm-1

region.

The infrared spectra of these compounds show a medium sharp

peak in the region 579-518 cm–1

for M-O stretching. The IR spectra of

alkaline earth metal stearates show prominent peaks between 3453-3418

cm–1

due to –OH stretching indicating the presence of water of

crystallization. These results correspond very well with Thermodynamic

analysis of the stated metal soaps.

The topographical study of these compounds in their solid

state has been facilitated by Field Emission Scanning Electron

Microscope and Energy Dispersive X-ray spectroscopy (EDAX). The

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conclusions drawn suggest that the potassium stearate has rough and

irregular textured surface whereas the particles of magnesium stearate are

of smooth and spongy appearance.

It seems that calcium stearate has rod like, smoother, more

homogenous microstructures and lamellar morphology. The angular,

irregular and fractured particles can be seen in strontium stearate. The

barium stearate particles are compact and irregular in shape and having

varying particle size.

The chapter 3 pertains to thermogravimetric analysis.

Thermogravimetric curves were obtained by employing Perkin Elmer

(Pyris Diamond) analyzer. The samples were well powdered before the

start of each run and heated in air (400 mg/min) at the heating rate of

10°C min-1

. Based on TG analysis, the mode of decomposition for

various alkaline earth metal stearates may be shown as under:

OXHM(RCOO)OM.XH(RCOO) 2soap)metald(Dehydrate

2soap)metal(Hydrated

22 ... (i)

moiety)ketonichigher(A

2Carbonate)Metal(

32 CORMCOM(RCOO) ...(ii)

2oxide)(Metal

3 COMOMCO

Here, X represents number of moles of water of crystallization, M

signifies for Mg, Ca, Sr and Ba metals and R signifies for higher alkyl

chain containing seventeen carbon atoms.

Several equations have been proposed to analyze the TG data.

The present chapter however emphasizes on thermal decomposition of

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alkaline earth metal stearates. The various models viz. Mechanistic,

Coats-Redfern and Horowitz-Metzger have been applied to evaluate both

energy of activation and the order for thermal decomposition of these

compounds. It is concluded that the order of reaction for both the

processes i.e. the loss of water of crystallisation and main decomposition

of these compounds generally follow first order kinetics.

The chapter 4 is related to Differential Thermal Analysis and

Differential Thermogravimetry. DTA/DTG techniques have been

successfully applied to the decomposition of alkaline earth metal

stearates. The results obtained have been substantiated by various kinetic

and thermodynamic parameters as deduced from them. Thermograms

were obtained by the same derivatograph under similar conditions as

mentioned in chapter 3. The thermodynamic results (∆G, ∆S) from DTA

are found to corroborate (∆G, ∆S) as obtained from DTG.

The chapter 5 includes Conductivity Measurements of the

alkaline earth metal stearates in mixed solvent (50% methanol + 50%

chloroform). The values of critical micelle concentration, CMC

(mol dm-3

), equivalent conductance at infinite dilution, ∞ (S cm2/g-eq),

degree of dissociation, α and dissociation constant, KD of alkaline earth

metal stearates in the stated solvent-mixture at different temperatures (30-

50°C) have been evaluated employing the data of specific conductivity.

Dissociation constant, KD is found to decrease with increasing

temperature. The dissociation of the alkaline earth metal stearates in

chosen solvent is supported by favourable negative enthalpy whereas

positive free energy and negative entropy are found to oppose the

process, i.e. the negative enthalpy change of dissociation tends to make

up for the unfavourable changes in free energy and entropy of the

Dissociation Process. On the other hand, the evaluated thermodynamic

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parameters for Association Process, negative free energy and positive

entropy favour this process while positive enthalpy opposes it. Thus there

is fair chance of aggregation in these soap solutions.

The conductivity of the surfactant solutions in presence of

additives was measured at different temperatures (30-50°C) in thermostat.

Additives (sodium citrate, chlorides of calcium and ammonium, sulphates

of sodium, manganese and potassium, calcium phosphates, oxides of zinc

and copper) in extremely low concentration 1.0 x 10-4

M were used to

show their efficacy in altering the cmc of these soap solutions (30-50°C).

Three concrete observations may thus be made from the

perusal of the data mentioned in tables (1-3). First, the cmc data are found

to decrease in presence of these additives. Secondly, the efficacy of

lowering the cmc for all the additives used in the present study is found to

follow the order as: sodium citrate, potassium sulphate, calcium

phosphate, sodium sulphate, ammonium chloride and calcium chloride.

However, manganese sulphate, zinc and copper oxide do not show any

appreciable effect upon the cmc of all the surfactants under study.

The chapter 6 is related to the theoretical evaluation of

various acoustic parameters including the Ultrasonic Velocity. It

suggests that the values for both molar volume, TV and available volume,

Va decrease with increasing concentration for both pre- and post micellar

regions. The decrease in inter-molecular free length, Lf with increasing

concentration (Tables 1-4) indicates that there is a significant interaction

between surfactant and solvent molecules, and that the structural

arrangement is considerably affected. The data for acoustic impedance Z

( gcm–2

s–1

), for alkaline earth metal stearates however vary between

(1.12 – 1.19) × 108. It is therefore inferred that a significant solute -

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solvent interaction is predominant in pre-micellar region (dilute

solutions), whereas probability of aggregation for surfactant molecules is

highly scarce in this region.

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FUTURE SCOPE

Biochemists, especially those working on membrane structure

and function, have long been aware of the selective solubilizing power of

surfactants for membrane components; chemists now know that

surfactants can modify chemical reactions; pharmaceutical scientists are

aware of the formulation potential of surfactants. A sincere effort is on to

put these threads together and to discuss the newer developments in

surfactant technology which will allow even greater progress in the

future.

Significantly, it is now more than forty years since a

monograph on solubilization by surface-active agents appeared. Since the

publication of that monograph the subject has expanded rapidly as the

unique potential of surfactants has become known to a wider circle of

scientists. The topic of catalysis in micellar media was in an early stage of

development in 1968 but the growth in this subject has given rise to an

excellent textbook by Fendler and Fendler.

Researchers have already aimed at varied disciplines such

as pharmacy (especially those specializing in pharmaceutics and

pharmaceutical technology), biochemistry, biology, chemistry, industrial

research and development laboratories exploring the value or problems of

surfactant systems. Other fascinating facets of this field may be

understood by going through the literature on surface activity, phase

behaviour, micellization, surface activity and colloidal properties of drugs

and naturally occurring substances, solubilization, pharmaceuticals

aspects of solubilization, biological implications of surfactant presence in

formulation, emulsions/micro-emulsions, surfactants in suspension

system, aspects of surfactant toxicity and reactivity in surfactant system.

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Recently, scientists have produced world's first magnetic

soap (Science Daily Jan. 23, 2012) from Bristol University have

developed soap, composed of iron rich salts dissolved in water, that

responds to a magnetic field when placed in solution. The soap‘s

magnetic properties were shown with neutrons at the Institut Laue-

Langevin to result from tiny iron-rich clumps that sit within the watery

solution. The generation of this property in a fully functional soap could

calm concerns over the use of soaps in oil-spill clean ups and

revolutionise industrial cleaning products.

Present study may thus be treated as a modest attempt

initiated with a view to understand and dwell into the physico-chemical

aspects of anionic surfactants, viz, metallic soaps that belong to a class of

anionic surfactants.

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LIST OF PUBLICATIONS

1. Tensides (or Surfactants) and Heavy Metal Soaps; P. Bahadur and

Simmi Tyagi, Asian J. Exp. Chem, (Dec, 2011); Vol. 6 (2): 119-122.

2. Interfacial Chemistry and Interface; P. Bahadur and Simmi Tyagi,

Asian J. Exp. Chem, (Dec, 2011); Vol. 6 (2): 123-127.

3. Acoustical Studies on Alkaline Earth Metal Stearates; P. Bahadur

and Simmi Tyagi (under preparation).

4. Thermal Analyses of Alkaline Earth Metal Stearates; P. Bahadur and

Simmi Tyagi (to be communicated).

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