Abstract:

The interfacial dilational rheological properties of 2, 5-diethyl-4-nonyl benzene sulfonate (292), 2, 5-dipropyl-4-nonyl benzene sulfonate (393), and 2, 5-dibutyl-4-nonyl benzene sulfonate (494) at air-water and decane-water interfaces were investigated by drop shape analysis. The influences of ageing time, interfacial pressure, dilational frequency, and bulk concentration on their dilational elasticity and viscosity were expounded. The surface adsorbed film was found to be elastic in nature at lower bulk concentration, and its strength determined by the interactions between the molecules in the film. In contrast, a diffusion-exchange process between the surface and the bulk controlled the properties of film at higher concentration. The insertion of oil molecules weakened the interactions among the adsorbed molecules, causing the diffusion-exchange process to dominate the nature of the interfacial film. However, this effect of the oil molecules decreased with increasing short alkyl chain length. The strength of the surface film could be determined before the adsorption equilibrium, while the nature of the interfacial film varied after saturated adsorption because of the re-arrangement of the interfacial surfactant molecules.

Key words: Alkyl benzene sulfonate, Surface, Interface, Dilational elasticity, Dilational viscosity