Two-dimensional self-assembly of colloids in thin liquid films

Abstract

This is a project report on research on the methodological development of monolayer films of particles with a crystalline order. The surface phenomena which we have derived are directional movement and assembly of fine colloid particles in thin liquid films. We have found that particles can self-assemble in a thin liquid layer when the layer thickness is properly controlled. Stable thin liquid films with a thickness comparable to the particle geometry are developed on a suitable surface to induce the particle self-assembly. Colloid particles, when mobile even in such a thin liquid film as barely containing the particles, are convectively assembled carried by water influx and hexagonally packed into crystalline-array films. Two distinct mechanisms are now postulated to explain this novel fabrication, (i) they are assembled by convective water flow, stimulated by evaporation at the boundary of the particle arrays (films), (ii) they are packed by the long-range attractive force acting between particles induced by surface tension at the film surface. Several thin liquid film systems have so far been developed for solid colloids such as latex particles using wettable solid surfaces such as glass, mica and silicon wafer and for protein molecules using wettable liquid surfaces such as mercury, fluorinated oil and glucose solution. Examples obtained with various proteins and polystyrene latex spheres are shown.