Dependence of aggregation behavior and physicochemical properties of bis-cationic surfactants on the polarity of surfactant head group

Abstract

Effect of variation in head group polarity on physicochemical properties of butane-1,4-bis(dodecyldimethylammonium bromide) surfactants has been examined through conductance, surface tension and viscosity measurements. The critical micellar concentration (cmc) was determined by surface tension and conductance measurements. Surface tension data was further used to determine the maximum surface excess concentration (Γmax), minimum area per molecule (Amin) at air/water interface and Gibb's free energy of adsorption (ΔG°ad). Effect of variation in head polarity on average degree of micelle ionization (αave), binding of counterions to the micelle (β) and thermodynamics of micellization was examined through conductance measurement. Effective Gibb's free energy (ΔG°eff) and cmc were observed to decrease with head group polarity indicating that increase in head group polarity favors micellization process as compared to adsorption at the air/water interface. The intrinsic viscosity (η) and hydration of micelle (hE) were observed to increase with polarity of head and decrease with temperature.