MONTE-CARLO SIMULATION OF INLAYER STRUCTURE FORMATION IN THIN LIQUID-FILMS

The structure formation in free liquid films containing surfactant mic elles or other colloidal particles is of fundamental importance in col loid and interface science and its applications. Experiments on thinni ng of single flat or curved symmetrical liquid films and asymmetrical or pseudoemulsion films formed from colloidal dispersions show that th ese films thin in a stepwise manner. We present here results of our gr and-canonical-ensemble Monte Carlo simulations using both the hard sph ere and Leonard-Jones potentials, which not only verify the presence o f particle layering inside the free thinning films but also reveal for the first time that, depending on the film thickness and particle vol ume fraction, there exists within the particle layers, in the directio n parallel to the film surfaces, an ordered 2-D hexagonal structure. T he calculated, in-layer radial distribution functions show that the in -layer structure transition depends on the film thickness and the posi tion of the layer inside the film. The sequence of the formation of mi crostructures in a thin film of fixed thickness with increasing partic le concentration is found to be disorder --> layering --> inlayer orde ring for the surface layers --> inlayer ordering for middle layers --> bulk type ordering. This ordering phenomenon in free liquid film is n ew. The formation of ordered structures inside the layers has practica l implications for both theology of such films and the film stability and thereby the dispersion stability.