Surface wave excitations and backflow effect over dense polymer brushes

TL;DR

This study uses Dissipative Particle Dynamics simulations to explore flow behavior over dense polymer brushes, revealing flow inversion caused by surface wave phenomena linked to collective polymer dynamics.

Contribution

It uncovers a novel flow inversion mechanism over dense polymer brushes driven by surface wave propagation, supported by simulation and theoretical analysis.

Findings

Flow inversion occurs at the brush interface for specific flow ranges.

Surface waves on the polymer brush surface are responsible for flow reversal.

The wave properties match solutions of the Stokes equations with traveling wave boundary conditions.

Abstract

Polymer brushes are increasingly used to tailor surface physicochemistry for various applications such as wetting, adhesion of biological objects, implantable devices, etc. We perform Dissipative Particle Dynamics simulations to study the behavior of dense polymer brushes under flow in a slit-pore channel. We discover that the system displays flow inversion at the brush interface for several disconnected ranges of the imposed flow. We associate such phenomenon to collective polymer dynamics: a wave propagating on the brush surface. The relation between the wavelength, the amplitude and the propagation speed of the flow-generated wave is consistent with the solution of the Stokes equations when an imposed traveling wave is assumed as boundary condition (the famous Taylor's swimmer).