Non-monotonic hydrodynamic lift force on highly-extended polymers near surfaces

TL;DR

This paper develops a theoretical model describing the non-monotonic hydrodynamic lift force on highly extended polymers near surfaces, revealing a maximum at the polymer's contour length and implications for polymer-surface interactions.

Contribution

The paper introduces a new analytical theory capturing the non-monotonic lift force behavior of extended polymers near surfaces, extending understanding beyond previous far-field results.

Findings

Lift force increases linearly with distance Z near the surface

Maximum lift force occurs at Z approximately equal to the polymer's contour length L

Force decays as Z^{-2} at large distances

Abstract

The hydrodynamic lift force that polymers experience near boundaries is known to be a crucial element when considering rheological flows of dilute polymer solutions. Here we develop theory to describe the hydrodynamic lift force on extended polymers flowing near flat surfaces. The lift force is shown to display a non-monotonic character increasing linearly with the distance to the wall $Z$ in the near-surface regime defined as $Z<L$, with $L$ being the contour length of the polymer. At heights $Z \sim L$ the lift force displays a maximum, and for $Z>L$ we recover the well known far-field result in which the force decays as $Z^{-2}$. Our analytical theory has important implications in understanding adsorption, desorption, and depletion layers of highly extended objects in flow.