Controlling colloidal sedimentation using time dependent shear

TL;DR

This study uses dynamical density functional theory to analyze how colloidal sediments respond over time to shear forces, revealing transient and steady-state behaviors including lane formation and migration.

Contribution

It introduces a theoretical framework to understand time-dependent colloidal sedimentation under shear, highlighting mechanisms of structural change and migration.

Findings

Transient packing enhancement at the wall

Migration of colloids away from the wall

Stationary oscillatory center-of-mass behavior

Abstract

Employing a recently developed dynamical density functional theory we study the response of a colloidal sediment above a wall to shear, demonstrating the time dependent changes of the density distribution and its center-of-mass after switching shear either on or off and under oscillatory shear. Following the onset of steady shear we identify two dynamical mechanisms, distinguished by their timescales. Shortly after the onset, a transient enhancement of the packing structure at the wall reflects the self-organization into lanes. On a much longer timescale these effects are transmitted to the bulk, leading to migration away from the wall and an increase in the center-of-mass. Under oscillatory shear flow the center-of-mass enters a stationary state, reminiscent of a driven damped oscillator.