A comparison of predicted and experimental critical micelle concentration values of cationic and anionic ternary surfactant mixtures using molecular-thermodynamic theory and pseudophase separation theory

Abstract

The surface and electrochemical properties of the cationic surfactants octyl-, decyl-, dodecyl-, tetradecyl- and hexadecyl trimethylammonium bromide (OTAB, DeTAB, DTAB, TTAB and HTAB, respectively) and sodium octyl-, decyl- dodecyl-, tetradecyl- and hexadecyl sulphates (SOS, SDeS, SDS, STDS, SHDS, respectively) in their ternary mixed states, have been studied. The critical micelle concentration (CMC), counter-ion binding, aggregation number, polarity, thermodynamics of interfacial adsorption and micellisation have been analysed by surface tension, conductivity and fluorimetry. Also investigated was the compatibility of the molecular-thermodynamic theory CMC calculation with experimental values obtained for the CMC using the above methods. The CMC values obtained using both βexp and βpred (molecular-thermodynamic theory monomeric interaction parameters obtained from experimental analyses and calculated values) were of the same order as the pseudophase separation approximation and the experimental CMC values. This shows the suitability of the molecular-thermodynamic theory to predict CMC values with only the singular species concentrations, molar ratios and singular CMC known. All methods have produced values that agree well and correlate closely with others previously reported.