The effects of hydrophobicity and orientation of cubic particles on the stability of thin films

A three-dimensional model of a single cubic particle in a thin liquid film has been developed using the Surface Evolver (Brakke, 1992) program. It has been used to investigate the effect of a particle’s contact angle on its energetically stable orientations at a liquid–vapour interface and how these, in turn, affect the particle’s ability to stabilise a thin film. It has been found that depending on the contact angle there are two possible stable orientations for a cubic particle (termed horizontal and rotated) at a liquid–vapour interface. For a film containing a cubic particle in a rotated orientation it has been found that the capillary pressure required to rupture the film is roughly 30% of that required for a film containing a particle of the same contact angle but in a horizontal orientation. The probability of a particle adopting one orientation over another is also investigated, showing that this too is affected by contact angle and leading to the conclusion that contact angle has a profound effect on non-spherical particles behaviour in thin films.