Behavior of colloidal particles and micelles in thin liquid films with application to foam stability.

摘要

Foams, emulsions and colloidal dispersions are frequently seen to occur in many industrial systems like ink, paint, milk, butter, shaving foams, etc. The key structural elements in these systems are the thin liquid films that form between the dispersed phase bubbles or droplets. Whenever two droplets or bubbles of different sizes come close together, the film formed between them is a curved film. Thus, experiments using surfactant-free, curved, single-foam-films containing colloidal particles were carried out to understand the effect of particle concentration, size, polydispersity, bidispersity and film size on the particle structuring phenomenon in the confined environment of a thin liquid film. Such layering provides additional stabilizing force and was also found to have a significant impact on the long-term stability of surfactant foams containing micelles. The work in this thesis using colloidal particles in curved films is the first of its kind.;Experimentally it was observed that the particles moved from the film to the bulk in the process of reaching an equilibrium and the flux of particles from the film periphery was a constant. A critical film size was observed for the curved films below which the particles did not show a tendency to leave the film. At high particle concentrations, the particle movement from the film to the bulk was low. Polydispersed and bidispersed particles displayed high rates of particle exodus from the film to the bulk, which are indicative of poor particle structuring in the thin liquid films. Particle behavior in confinement was satisfactorily explained using the diffusive-osmotic model. Our preliminary studies also show that micelles with higher ability to form ordered layers in a confined environment display a higher pollutant removal efficiency from solid surfaces.;Monte Carlo simulations of mono and bidispersed particles in thin liquid films corroborated the experimental observations. Particle layering was pronounced at high concentrations and the energy barrier for diffusion from the film to the bulk was high. The large particles in a bidispersed system, showed a unique phase separation behavior in confinement even at particle size ratios smaller than that needed for phase separation in the bulk.