(464d) Gravitational Collapse of Reversible Colloidal Gels Via Large-Scale Dynamic Simulation

We investigate the phenomenon of gravitational collapse in colloidal gels via dynamic simulation. In moderately concentrated gels formed via arrested phase separation, rupture and re-formation of bonds of strength O(kT) permit ongoing structural rearrangements that lead to temporal evolution â?? aging â?? of gel structure and rheology. The reversible nature of the bonds also allows the gel to transition from solid-like behavior to liquid-like behavior under external forcing, and back to solid-like behavior when forcing is removed. But such gels have also been shown to be susceptible to sudden and catastrophic collapse of the entire structural network, after which the gel sediments into a dense layer, eliminating any intended functionality of the network scaffold. Although the phenomenon is well studied in the experimental literature, the microscopic mechanism underlying the collapse is not understood. To study this behavior, we conduct large-scale dynamic simulation to model structural and rheological evolution in colloidal gels subjected to gravitational stress, examining the detailed micro-mechanics in three temporal regimes: slow, pre-collapse evolution; collapse and rapid sedimentation; and long-time compaction. A range of attraction strengths and gel ages, and their effect on the critical force that triggers collapse, are studied.