DYNAMICS OF COLLOID POLYMER MIXTURES

We report a preliminary study of the dynamics of mixtures of ''hard-sphere'' colloidal particles and non-adsorbing polymer, in which the polymer induces a ''depletion'' attraction between the particles. Moderate concentrations of polymer cause the suspensions to separate into coexisting colloidal fluid and colloidal crystalline phases, whereas more polymer leads to ''gel'' states in which crystallization is suppressed. Studies of the intensity of scattered light at low angles and dynamic light scattering at larger angles suggest the following picture of the gels. Initial rapid diffusion-limited aggregation of the particles via the depletion attraction produces a close-packed assembly of clusters. Subsequent slower consolidation of the clusters weakens them to the point where they no longer support their weight and gravitational settling occurs.