Chain extension of a confined polymer in steady shear flow

TL;DR

This study models how confinement in narrow capillaries reduces polymer chain extension under shear flow, aligning well with experimental observations of DNA stretching near surfaces.

Contribution

It introduces a theoretical framework combining Rouse-Zimm dynamics with finite extensibility to analyze confined polymer behavior in shear flow.

Findings

Polymer extension is significantly reduced by confinement.

Extension varies with shear rate in a manner consistent with experiments.

Model aligns qualitatively with experimental DNA stretching data.

Abstract

The growing importance of microfluidic and nanofluidic devices to the study of biological processes has highlighted the need to better understand how confinement affects the behavior of polymers in flow. In this paper we explore one aspect of this question by calculating the steady-state extension of a long polymer chain in a narrow capillary tube in the presence of simple shear. The calculation is carried out within the framework of the Rouse-Zimm approach to chain dynamics, using a variant of a nonlinear elastic model to enforce finite extensibility. Under the assumption that the sole effect of the confining surface is to modify the pre-averaged hydrodynamic interaction, we find that the calculated fractional chain extension x is considerably smaller than its value in the bulk. Furthermore, the variation of x with a dimensionless shear rate (the Weissenberg number, Wi) is in good qualitative agreement with data from experiments on the flow-induced stretching of lambda- phage DNA near a non-adsorbing glass surface.