Micelle formation by anionic and cationic surfactants in binary aqueous solvents

Abstract

Conductances of sodium dodecylsulfate (SDS) and cetyltrimethyl ammonium bromide (CTAB) have been determined in the binary mixtures of ethylene glycol (EG)–H₂O, glycerol (Gly)–H₂O, N,N-dimethylformamide (DMF)–H₂O and dimethyl sulfoxide (DMSO)–H₂O. The measurements were made at 25 °C with EG concentrations up to 75 vol.% and other co-solvent concentrations up to 50 vol.%. Conductances of SDS have also been performed in the presence of L-glutamic acid, 18-crown-6 ether (CR) and sucrose in H₂O. From the conductivity data, the critical micellar concentration, c.m.c., the counter ion dissociation constant, β, the standard Gibbs' free energy change of the micellisation, ΔG^⊖_m, and in some cases the molar equivalent conductance at infinite dilution, Λ₀, of these surfactants have been determined.

A comparative study of the thermodynamics of micellisation for SDS and CTAB in the presence of various non-aqueous co-solvents reported here and earlier, reveals that tetrahydrofuran (THF) has the highest ability to break the micelles. On the other hand, the presence of additives like glutamic acid, CR and sucrose lead to micelle stabilisation.