Clusters and gels in systems of sticky particles

We studied clustering and gelation in low-volume-fraction () hard-sphere colloids, some with charge, with added non-adsorbing polymers. The range of the effective 'depletion' attraction induced by the polymers between the particles is of the particles' diameter. The effects of density mismatch between the particles and the solvent and unscreened charges on the particles were investigated. The onset of aggregation and gelation in a neutral, density-matched system is discussed in terms of mode-coupling theory (MCT) and a recent 'renormalized' version of MCT respectively. Gravity causes sedimentation of growing clusters and shifts the gelation boundary. In the charged and density-matched system, a 'cluster phase' in which finite-size aggregates 'coexisted' with monomers occurred before gelation. Its origins remain unclear.