Conductometric and molecular dynamics studies of the aggregation behavior of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) in aqueous and electrolytes solution

Abstract

Herein, we have studied the mixed micellization of Cetyltrimethylammonium bromide (CTAB) and Sodium dodecyl sulfate (SDS), in aqueous/various salts medium at several temperatures (298.15–318.15 K) by conductivity measurement method. The extent of interaction between CTAB and SDS was assessed from the values of ideal critical micelle concentration (cmc id ) as well as experimental cmc. In attendance of salts, cmc values are obviously decreased from the corresponding values in aqueous medium. The magnitudes of micellar mole fraction of CTAB (X 1 ) and activity coefficients of CTAB & SDS (f 1 & f 2 ) were estimated based on different theoretical model and outcome disclose the effective involvement of CTAB in the mixed micellization. The executed values of both interaction parameters (β) and excess free energy of micellization were negative signifying the attractive interaction and stability of mixed micelles respectively. The executed negative values of Gibbs free energy change of micellization, ∆G om illustrate the spontaneous micellization of individual/mixed surfactant system. The other thermodynamic parameters ΔH om (enthalpy change), and ∆S om (entropy change) were also calculated from the conventional standard equations. Molecular level interactions are disclosed by molecular dynamics (MD) simulation which showed that salts promote more interactions between the surfactants.