Network-forming phase separation of colloidal suspensions

Colloidal suspension can be regarded as an ideal model system of emulsions, protein solutions, foods, and inks. When there are strong attractive interactions between colloidal particles, they aggregate, phase separate, and sometimes form gel. The basic understanding of the resulting formation of superstructures is of crucial importance from both the scientific and industrial viewpoints. Here we provide clear experimental evidence suggesting that phase separation of colloidal suspensions can take the following kinetic pathway accompanying a metastable transient gel state: upon the phase separation, a percolated network is formed by a hierarchical clustering mechanism even at an extremely low colloid volume fraction (<10−3). Then the network structure coarsens with time under the influence of the connectivity and the resulting self-generated mechanical stress. The similarity of this behaviour to droplet-forming viscoelastic phase separation in a dilute polymer solution suggests that colloid phase separation may be classified as viscoelastic phase separation.