Cyclic motion and inversion of surface flow direction in a dense polymer brush under shear

TL;DR

This study uses molecular simulations to explore how dense polymer brushes under shear flow exhibit cyclic motion and can invert local flow direction, revealing complex surface-fluid interactions.

Contribution

It demonstrates that dense polymer brushes induce flow inversion and cyclic chain motion, extending understanding of surface flow behavior under shear conditions.

Findings

Polymer chains exhibit cyclic tumbling motion under shear.

Flow inversion occurs near brush-coated surfaces.

Surface effects can be partially described by Navier slip conditions.

Abstract

Using molecular simulations, we study the properties of a polymer brush in contact with an explicit solvent under Couette and Poiseuille flow. The solvent is comprised of chemically identical chains. We present evidence that individual, unentangled chains in the dense brush exhibit cyclic, tumbling motion and non-Gaussian fluctuations of the molecular orientations similar to the behaviour of isolated tethered chains in shear flow. The collective molecular motion gives rise to an inversion of hydrodynamic flow direction in the vicinity of the brush-coated surface. Utilising Couette and Poiseuille flow, we investigate to what extend the effect of a brush-coated surface can be described by a Navier slip condition.