Hydrodynamic Signatures in Colloidal Gels: From Network Formation to Gravitational Collapse

Abstract

Colloidal gels arise when attractive particles dispersed in a liquid form an open, system-spanning network. Although such materials are predominantly liquid, their microstructure imparts solid-like mechanical properties that are central to their use in food, cosmetics, coatings, and other soft matter applications. Yet, the connection between microscopic structure, macroscopic mechanics, and long-time stability of colloidal gels remains incompletely understood. This thesis addresses this problem through a combination of advanced simulations and theoretical modeling. A key contribution is the development of JFSD, a modern, high-performance implementation of Fast Stokesian Dynamics. This method enables accurate simulations of thousands of colloidal particles interacting via hydrodynamic coupling through the surrounding fluid. Using JFSD, we demonstrate that hydrodynamic interactions — the fluid-mediated, many-body effects by which particles influence each other’s motion — critically affect gel formation, restructuring, and aging. These results highlight the limitations of approaches that neglect such interactions and provide new microscopic insight into gel dynamics. Building on these simulation results, we revisit theoretical descriptions of gel gravitational collapse, a process whereby the network ultimately fails under its own weight. Classical models treat gels as porous elastic solids with uniform resistance to deformation. Here, we extend these frameworks by incorporating microscopic features of the network, in particular a local viscosity that quantifies how the gel resists internal flow and rearrangement. This refinement leads to the prediction of previously overlooked timescales that govern the onset and progression of collapse. These new timescales help explain experimental observations that could not be reconciled with earlier models, thereby advancing our understanding of gel failure mechanisms. To connect theory and simulation directly with experiment, we initialize our models with particle coordinates obtained from confocal microscopy of real colloidal gels. This integration provides a quantitative bridge between measured microstructures and simulated dynamics, enabling a more faithful description of experimental systems. In doing so, we establish a framework where experimental data can be directly tested against large-scale simulations and continuum-level theory. Overall, the work presented in this thesis delivers both new computational tools and theoretical concepts for the study of colloidal gels. The development of JFSD makes it possible to investigate hydrodynamic interactions in gelation and aging with unprecedented accuracy and efficiency. The extension of collapse theory introduces essential microscopic ingredients that alter the predicted macroscopic dynamics. Finally, the direct connection between simulations and experiments strengthens the link between fundamental understanding and practical application. Beyond colloidal gels, the approaches and insights developed here are relevant to a broad class of soft matter systems where particle-fluid interactions and network dynamics play a central role, including industrial formulations and biological tissues.