(411g) Hydrodynamics of Colloidal Arrays Under Quasi-Two Dimensional Confinement

The flow-induced structure of small ensembles of colloidal particles in confinement is important to a number of applications in microfluidics. However, experimental limitations in creating pre-defined configurations of particles have prevented a detailed study of many-body hydrodynamic interactions in such colloidal arrays. In this work, we use the recently developed stop flow lithography technique as an in situ method to create patterned colloidal arrays of polymer gel particles with well-defined size, shape, and rigidity in microfluidic channels, providing a flexible platform to study their response to flow under quasi-two dimensional confinement. We explore the effects of flow on arrays of prototypical colloids with positive curvature (discs), zero curvature (squares), and negative curvature (stars) under various types of lateral confinement (including straight and tapered channels), demonstrating a rich family of behavior that can be tuned by both the initial configuration of particles and the applied flow conditions. These observations are reconciled using a computational technique that captures fluid/structure interaction by coupling Lattice Boltzmann with a rigid body integrator (for stiff particles) or a Lattice Spring model (for deformable particles). The simulations reveal how the observed behavior arises from the interplay of short-range interactions sensitive to particle geometry and generic long-range many-body interactions. The results expose new motifs for controlling the flow and assembly of colloids in quasi-two dimensional confinement, and have implications in a number of phenomena, including jamming, dispersion, and colloidal assembly.