The London—van der Waals force between two approaching droplets: The consequences of flattening of the spherical bodies

Abstract

The analytical expressions for the non-retarded London—van der Waals potential of two identical flattened spheres and the existing force between them have been derived. The results obtained extend the applicability of “classical” Hamaker-type equations. In the limiting cases (small distance, large distance, weak and strong flattening) the expressions known from the literature are obtained. Calculations show that for flattened droplets the London—van der Waals force increases drastically compared to that for spherical droplets. Flattening governs the contact angle between the film and the droplet meniscus which result of hydrodynamic forces under dynamic conditions. This flattening can also have a thermodynamic origin. For strong flattening, the London—van der Waals force contributes only in a small way to the total free energy, and such flattening originates mainly from the lower interfacial energy of the film which is highly influenced by the interaction between the emulsifier and the continuous phase.