Hydrodynamic stability criterion for colloidal gelation under gravity

Abstract

Attractive colloids diffuse and aggregate to form gels, solid-like particle networks suspended in a fluid. Gravity is known to strongly impact the stability of gels once they are formed. However, its effect on the process of gel formation has seldom been studied. Here, we simulate the effect of gravity on gelation using both Brownian dynamics and a lattice-Boltzmann algorithm that accounts for hydrodynamic interactions. We work in a confined geometry to capture macroscopic, buoyancyinduced flows driven by the density mismatch between fluid and colloids. These flows give rise to a stability criterion for network formation, based on an effective accelerated sedimentation of nascent clusters at low volume fractions that disrupts gelation. Above a critical volume fraction, mechanical strength in the forming gel network dominates the dynamics: the interface between the colloid-rich and colloid-poor region moves downward at an ever decreasing rate. Finally, we analyze the asymptotic state, the colloidal gel-like sediment, which we find not to be appreciably impacted by the vigorous flows that can occur during the settling of the colloids. Our findings represent the first steps toward understanding how flow during formation affects the life span of colloidal gels.

Hydrodynamic lubrication in colloidal gels

“…The efficiency comes at the cost of neglecting HIs at any relative distance, which means that this approximation produces unrealistic dynamics for suspended colloids. This is not an issue for studying equilibrium systems, though it strongly affects the dynamics of formation 31–35,41 and collapse 18,45 in colloidal gels.…”

“…Over the past two decades, various research groups have performed numerical studies of colloidal gels that account for HIs. 18,19,31–36,39–45 Introducing HIs into particle simulations poses a significant challenge. In the friction-dominated regime appropriate to colloidal hydrodynamics, a Newtonian fluid satisfies the Stokes equations.…”

Colloidal and Thermal Stability of Three‐Component Hybrid Materials Containing Clay Mineral, Polysaccharide and Surfactant

“…This process depends mainly on the physicochemical and rheological properties of the system [27,28] . It should be emphasized that the particle dispersion in a solvent can be colloidally stable (there is no change in the particle size) while it is gravitationally unstable (particles settle due to unmatched density with the solvent) but it should be highlighted that destabilization of the colloidal system usually leads to gravitational instability (larger particles start to settle down quickly) [29,30] …”