Controlling wall particle interactions with activity

TL;DR

This paper investigates how active nematic liquid crystals influence the effective forces on hard disks near walls, revealing that activity type and anchoring conditions determine attraction or repulsion of the disks.

Contribution

It provides exact expressions for forces on disks near walls in active nematics, highlighting how activity and anchoring conditions affect disk-wall interactions.

Findings

Extensile activity attracts planar anchored disks to walls.

Contractile activity repels planar anchored disks from walls.

Normal anchoring shows opposite behavior, with attraction in contractile systems.

Abstract

We calculate the effective forces on hard disks near walls embedded inside active nematic liquid crystals. When the disks are sufficiently close to the wall and the flows are sufficiently slow, we can obtain exact expressions for the effective forces. We find these forces and the dynamics of disks near the wall depend both on the properties of the active nematic and on the anchoring conditions on the disks and the wall. Our results show that the presence of active stresses attract planar anchored disks to walls if the activity is extensile, and repel them if contractile. For normal anchored disks the reverse is true; they are attracted in contractile systems, and repelled in extensile ones.