Simulating particle stabilised thin films using surface evolver

The behaviour of particle stabilised thin films is key to the performance of many industrial processes. One example is froth flotation, used in the mining industry to concentrate low grade ores of platinum, gold or copper. A particle stabilised froth is used to separate the desired, valuable minerals from the waste, or gangue. Due to the highly dynamic nature of the system, the behaviour of the particles attached to the films in the froth is difficult to observe experimentally. It is therefore expedient to develop computer models of the particle stabilised films to allow investigation of the fundamental aspects of this system. Particle shape, hydrophobicity and packing arrangement all cause distortion of the liquid-vapour interface of the film. This affects the forces acting on the particles and the capillary pressure required to rupture the film. The Surface Evolver (Brakke, 1992) program has been used to create several different models of particles in films and investigate these effects. Surface Evolver is a program that uses an iterative minimisation approach to find the minimum energy shape of a user defined set of surfaces. As such it is well suited to studying the problem of particles at interfaces and the deformations that they create. Approaches to modelling both spherical and non-spherical particles in thin films using Surface Evolver will be introduced. The relationship between particle packing, contact angle and maximum sustainable capillary pressure (Pcrit) for spherical particles in a thin film has been investigated using this approach, results from which will also be discussed.