Ordered states in systems of macroscopic particles

Abstract

ONE of the most striking observations of systems consisting of macroscopic particles (∼ 1 µm in diameter) dispersed in a uniform background, is that in certain circumstances the particles can form themselves into an ordered or solid-like array. The importance and significance of these structures to a wide range of materials, including virus suspensions, soils, lacquers and latices, was recently discussed quite extensively by Efromov¹. In recent years this has also been the subject of considerable experimentation on well characterised polystyrene latices^2–4. We have developed a theoretical model for a stable colloidal dispersion⁵ in which this disorder–order transition in a system of macroscopic particles is treated as the analogue of the fluid–solid transition in molecular materials. This theoretical approach shows that this ordering is a consequence of the repulsive forces between the particles. We show the more detailed features of the structure of the disordered and ordered phases of systems of colloidal or macroscopic particles.