Clusters in colloidal dispersions with a short-range depletion attraction: Thermodynamic identification and morphology

Hypothesis: Particle aggregation is ubiquitous for many colloidal systems, and drives the phase separation or the formation of materials with a highly heterogeneous large-scale structure, such as gels, porous media and attractive glasses. While the macroscopic properties of such materials strongly depend on the shape and size of these particle aggregates, the morphology and underlining aggregation physical mechanisms are far from being fully understood. Recently, it has been proposed that for reversible colloidal aggregation, the cluster morphology in the case of colloids interacting with short-range attractive forces is determined by a single variable, namely, the reduced second virial coefficient, B2∗. Experiments: We examined this proposal by performing confocal microscopy experiments and computer simulations on a large collection of short-ranged attractive colloidal systems with different values of the attraction strength and range. Findings: We show that in all cases a connection between the colloidal cluster morphology and B2∗ can be established both in experiments and simulations. This physical scenario holds at all investigated thermodynamic conditions, namely, in the fluid state, in the metastable region and in non-equilibrium conditions. Our findings support the connection between reversible colloidal aggregation and the so-called extended law of corresponding states.