Colloidal Gel Network
Colloidal suspensions can be regarded as an ideal model system for emulsions, protein solutions, foods, and inks. When colloidal particles strongly attract with each other, they aggregate, phase-separate, and sometimes form gel. The basic understanding of this spatially heterogeneous jamming process is of crucial importance from both the scientific and industrial viewpoints. Here we study this problem using a “fluid-particle dynamics” simulation, which properly incorporates interparticle hydrodynamic interactions. Upon phase separation, a percolated network of colloidal particles is formed with a help of hydrodynamic interactions. Then the network structure coarsens with time by repeating the following elementary process: stress concentration at a weak part of the network, its breakup and the resulting mechanical relaxation to a new metastable state, and the stress concentration again. Contrary to the common belief, the coarsening proceeds even without any thermal noise: the thermal activation is not prerequisite for this type of coarsening. We show that the coarsening is primarily driven by self-generated mechanical stress. This remarkable kinetic pathway of purely mechanical origin may be universal to any mixtures with strong dynamic asymmetry between their components, such as polymer solutions, colloidal suspensions, emulsions, and protein solutions. This may have a significant implication on our basic understanding of network formation in soft- and bio-matter.