Theoretical analysis of film thickness transition dynamics and coalescenceof charged miniemulsion droplets

The kinetics of thickness transitions of the film, separating two electrost atically stabilized emulsion droplets, is studied. The film evolution is co nsidered as a random process in the two-dimensional space of the film radiu s and thickness. The analysis is based on the Smoluchowski equation for the time dependent probality for realization of a given configuration (film ra dius and thickness). The combination of attractive and repulsive (van der W aals and electrostatic) energies determines the potential energy term in th e Smoluchowski equation, while the hydrodynamic resistance of film thining determines the diffusion tensor. The components of the latter are calculate d. This approach allows one to obtain the average escape time from the seco ndary (common film) to the primary (Newton black film) energy minimum. This is equivalent to the common film lifetime. If there are not any short-rang ed repulsions, to stabilize the thin (Newton black!film) the droplets fuse and the average escape time becomes that for coalescence. It is shown that the droplet deformability may have a great impact on the kinetics of film t hickness transition. This is particularly important for emulsion systems wi th low interfacial tension and high electrolyte concentrations.