A study of micellization and the thermodynamic properties of a series of aqueous sodium cyclohexyl alkanoate surfactants

Abstract

The micellization and the thermodynamic properties of a series of sodium cyclohexyl alkanoates of the general formula C6H11(CH2)nCOONa (where n = 1, 2, 3, 4) were investigated employing conductivity, density, surface tension, viscosity, speed of sound, luminescence probing experiments, and Fourier transform infrared (FT-IR) spectroscopy. The critical micelle concentrations (cmcs) and the aggregation numbers indicate that these surfactants have high cmc values and low aggregation numbers when compared to other single-headed surfactants (most notably the sodium alkanoates). Thermodynamic properties, obtained from the mass action model, indicate that micellization is spontaneous and entropically driven. The saturation area per molecule, the free energies of adsorption, and the efficiency and effectiveness of adsorption were determined through surface tension measurements. The presence of the cylcohexyl ring appears to influence the surface properties of micellization. Both the effectiveness and the efficiency of these surfactants, in lowering the surface tension of water, are lower than that of the straight chain alkanoates.Key words: thermodynamics, micellization, aggregation numbers, speed of sound, and spectroscopy.