(375a) Dynamics Of Meniscus-Bound Particle Clusters in Flow

Capillary suspensions are three-phase mixtures containing a solid particulate phase, a continuous phase liquid, and a second immiscible liquid phase. Capillary suspensions are used in a diverse array of applications including 3D printing, porous materials, and food formulations. Despite recent progress, the micromechanics of capillary-bound clusters in non-equilibrium flow is not fully understood. In this work, we study the dynamics of meniscus-bound particle clusters in extensional flow using the Stokes trap, which is an automated flow method allowing for precise control of fluid flow for manipulating and studying freely suspended particles. Beginning with two-particle doublets, we observe how particle clusters rearrange and deform in extensional flow. The critical capillary number Ca required for rupture is quantified, and the dependence of cluster breakup time on meniscus volume is characterized. In addition, cluster relaxation experiments are performed to characterize the timescale required for deformed particle clusters to return to their initial state starting from a stretched configuration after flow stoppage. In all cases, experiments are complemented by an analytical model that accounts for capillary forces, hydrodynamic drag forces, and hydrodynamic interactions acting on the particles. Results from the analytical model are found to be in good agreement with experiments. Overall, our work provides a new understanding of the non-equilibrium deformation dynamics of capillary clusters in flow.