Structure and Dynamics of Colloidal Dispersions

Abstract

In a dilute enough colloidal dispersion the particles are sufficiently far apart to be oblivious of each other’s presence. Correlations between the positions of different particles are essentially negligible - the static structure factor has value 1 at all wavevectors. Each particle undergoes its own Brownian motion, a random-walk diffusion resulting from numerous collisions with the molecules of the liquid suspension medium. By contrast, in a concentrated dispersion there is a characteristic structure, similar to that of atoms in a simple liquid, comprising a typical particle and its ‘cage’ of neighbours. This structure gives rise to the characteristic ‘diffraction peak’ in the structure factor. Now a particle’s motion is affected not only by the liquid-induced Brownian forces but also by both direct interparticle forces (Coulombic, hard-sphere etc.) and indirect hydrodynamic interactions transmitted through the liquid.