Colloidal glasses

At high enough concentrations, suspensions of microscopic particles in a liquid can form 'colloidal glasses'. These are metastable amorphous solids in which the particles are trapped by their neighbours but still have some freedom for local Brownian motions. Typically they are 'soft' solids which yield and flow under applied stresses. This article describes some experimental studies of colloidal glasses of spherical particles. The Brownian dynamics of quiescent, unstressed, systems can be measured using dynamic light scattering. Various rheological techniques give information on mechanical properties and the mechanisms of yielding. Emphasis is on exploring the striking differences between glasses formed by particles with purely repulsive interactions and those with additional short-ranged attractions.