Adsorption Kinetics at Liquid-Liquid Interfaces in Microgravity Conditions. Experimental Approach and Theoretical Background

A new method (Pressure Derivative Method), for measuring interfacial tension between immiscible fluids phases at zero Bond number, has recently been developed by Passerone et al. In the present work the method is extended to measurements of non-equilibrium interfacial tension. It allows to follow the kinetics of diffusion and/or adsorption to the interface, of a surfactant solved in the external phases, in which the drop has been rapidly grown. The development of the experimental procedure allowing to obtain the dynamic interfacial tension from dynamic capillary pressure data is presented. Furthermore, a theoretical part is presented, proposing a new equation describing the dynamics of the interfacial aging, obtained by considering the adsorption as an extended diffusion process with boundary conditions deduced from microscopic considerations. This equation allows to interpreted experimental data, and to deduce, from them, the molecular activation energies for adsorption and desorption.