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 degrees C from conductance measurements. In the range of alcohol mole fraction, x(2), 0 < x(2) < 0.00 8 the cmc decreased by a function of x(2) 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 th e concentration of these additives was increased, cmcs levered off and the effect of temperature tends to be insignificant. Thermodynamic parameters o f micellization, enthalpy (Delta H-m(0)), entropy (Delta S-m(0)) and free e nergy (Delta G(m)(3)) were determined from temperature dependence of cmc. T he solvent composition dependence of these thermodynamic parameters is dete rmined in terms of the effect of additives on micellizaffon of SDS. It is o bserved that both Delta H-m(0) and Delta S-m(0) bear out not only the obser ved order of decrease in cmc, but also account reasonably the effects produ ced by differences in alkyl chain configuration for these isomeric alcohols . In all cases Delta G(m)(0) < 0, and remained practically constant over th e entire solvent composition range studied. It is suggested that due to dif ferent structural consequences of intermolecular interactions both enthalpy and entropy must differ in a mutually compensating manner so that Delta G( m)(0) is not significantly affected. (C) 2000 Elsevier Science B.V. All rig hts reserved.