# Polymer brush collapse under shear flow

## TL;DR

This study investigates how polymer brushes on surfaces collapse reversibly under shear flow, with the collapse driven by free chains in solution, revealing potential for dynamic surface control.

## Contribution

It combines neutron reflectometry and simulations to show shear-induced reversible collapse of polymer brushes governed by free chains, advancing understanding of shear-responsive surfaces.

## Key findings

- Brush collapse increases with shear rate.
- Collapse is governed by free chains, not the brush itself.
- Reversible and reproducible collapse observed.

## Abstract

Shear responsive surfaces offer potential advances in a number of applications. Surface functionalisation using polymer brushes is one route to such properties, particularly in the case of entangled polymers. We report on neutron reflectometry measurements of polymer brushes in entangled polymer solutions performed under controlled shear, as well as coarse-grained computer simulations corresponding to these interfaces. Here we show a reversible and reproducible collapse of the brushes, increasing with the shear rate. Using two brushes of greatly different chain lengths and grafting densities, we demonstrate that the dynamics responsible for the structural change of the brush are governed by the free chains in solution rather than the brush itself, within the range of parameters examined. The phenomenon of the brush collapse could find applications in the tailoring of nanosensors, and as a way to dynamically control surface friction and adhesion.