Micellization of ionic surfactants in aqueous-rich region of organic solvants: A conductometric study of micellization behaviour of sodium dodecylsulfate in aqueous-rich region of 1-BuOH, 2-BuOH, t-BuOH at different temperatures

The critical micelle concentration (cmc) of sodium dodecyl sulfate (SDS) is determined in aqueous-rich region of 1-butanol (1-BuOH), 2-butanol (2-BuOH) and tertiary-butanol (t-BuOH) at 25, 35 and 45°C from conductance measurements. In the range of alcohol mole fraction, x2, 0<x2<0.008 the cmc decreased by a function of x2 in the order: 1-BuOH>2-BuOH>t-BuOH. Though not very significant, a relatively weak effect of temperature was observed in increasing the cmc in this narrow composition range. As the concentration of these additives was increased, cmcs levered off and the effect of temperature tends to be insignificant. Thermodynamic parameters of micellization, enthalpy (ΔHm0), entropy (ΔSm0) and free energy (ΔGm0) were determined from temperature dependence of cmc. The solvent composition dependence of these thermodynamic parameters is determined in terms of the effect of additives on micellizaffon of SDS. It is observed that both ΔHm0 and ΔSm0 bear out not only the observed order of decrease in cmc, but also account reasonably the effects produced by differences in alkyl chain configuration for these isomeric alcohols. In all cases ΔGm0<0, and remained practically constant over the entire solvent composition range studied. It is suggested that due to different structural consequences of intermolecular interactions both enthalpy and entropy must differ in a mutually compensating manner so that ΔGm0 is not significantly affected.