Kinetic and thermodynamic parameters of interaction between aqueous solutions of surfactants and oil films

Interaction of water solutions of surfactants with oil films has been studied to monitor the kinetics of their washing off a solid surface within the temperature range 25-75 °С. Correctness of detergent effect consideration for water solutions of surfactants in relation to oil films in the context of transport processes has been confirmed, and the analytical equation for the process kinetics has been specified. The correspondence of temperature dependence for the process parameters and oil viscosity has been demonstrated. Incorrectness of consideration of these two transport processes only on the basis of activation energy has been discovered; for the first time the calculation procedure of all their thermodynamic parameters has been developed. They are in good agreement with the experimental data obtained by radically different methods. It has been determined that the Gibbs potential of detergent effect for surfactant solutions in relation to oil films changes its sign at T = T*, where T* is the phase transition temperature in oil. Consequently, at T T*. A mechanism of the surfactant detergent effect has been suggested, based on the discovery that the detergent effect is maximal for surfactants with the hydrophilic-lipophilic balance value 10±2, which corresponds to the maximal surfactant solubilizing effect. It has been suggested that the activation energy of the detergent effect is determined by the potential barrier, which a straight surfactant micelle is to penetrate in order to infiltrate into the interphase layer on the oil film surface. Owing to destructurization of the interphase layer the probability of infiltration for other micelles increases. As a result a microindentation on the oil film surface is formed due to ability of straight micelles to solubilize oil, in time it increases in both depth and area, which ensures the oil film rupture. Therefore, the transport process that determines the surfactant detergent effect is conditioned by the movement of straight micelles following the interphase oil-water layer displacement owing to appearance of microindentations in the film, caused by the solubilization of oil particles by the micelles.