Particle stabilised thin films

• Main Author: Morris, Gareth David Morte
• Other Authors: Cilliers, Jan
• Published: Imperial College London 2010
• Subjects: 622
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.527771

Froth flotation is widely used by the mining industry to concentrate low grade metal ores. It uses the differences in surface properties between particles of the desired mineral and waste material to separate them using a mineralised froth. The properties of this particle stabilised mineralised froth impact on the efficiency of the separation process. Due to its dynamic and unstable nature it is difficult to study and remains relatively poorly understood. A deeper insight into the fundamental froth properties can be gained by using computer modelling techniques. Here a series of models are developed using the Surface Evolver (Brakke 1992). They are used to investigate the effects of particle shape, hydrophobicity and packing arrangement on the critical capillary pressure of thin films. Three dimensional simulations of uniformly spaced spherical particles in the film are compared to existing two dimensional (2D) analytical models. It is shown that 2D models over predict the capillary pressure required to rupture the film. The models are developed further to simulate randomly distributed particles in a periodic film. The results are then used to derive an expression for film stability based on particle packing density and contact angle. The different possible failure modes of double layers of particles are also investigated and the conditions under which they occur identified. A versatile model for simulating non-spherical particles in an interface or film is also derived and used to find the energetically stable orientations of orthorhombic particles at an interface. This information is then used to investigate the effect of particle orientation on the capillary pressure required to rupture the film. It is shown that the combination of contact angle and shape affect the particle orientation. Certain orientations are then shown to reduce the critical capillary pressure of the film by up to 70 %.