Adsorption-Induced Slip Inhibition for Polymer Melts on Ideal Substrates

TL;DR

This study investigates how physical adsorption of polymer chains at the solid/liquid interface affects slip behavior in polymer melts, extending the Navier-de Gennes model to better match experimental data from capillary leveling.

Contribution

The paper introduces an extended Navier-de Gennes model incorporating adsorbed chain density, explaining slip inhibition in polymer melts on ideal substrates at lower shear rates.

Findings

Adsorbed polymer chains significantly influence slip length.

Extended model aligns well with capillary leveling experiments.

Physical adsorption explains deviations from ideal slip behavior.

Abstract

Hydrodynamic slip of a liquid at a solid surface represents a fundamental phenomenon in fluid dynamics that governs liquid transport at small scales. For polymeric liquids, de Gennes predicted that the Navier boundary condition together with the theory of polymer dynamics imply extraordinarily large interfacial slip for entangled polymer melts on ideal surfaces; this Navier-de Gennes model was confirmed using dewetting experiments on ultra-smooth, low-energy substrates. Here, we use capillary leveling - surface tension driven flow of films with initially non-uniform thickness - of polymeric films on these same substrates. Measurement of the slip length from a robust one-parameter fit to a lubrication model is achieved. We show that at the lower shear rates involved in leveling experiments as compared to dewetting ones, the employed substrates can no longer be considered ideal. The data is instead consistent with physical adsorption of polymer chains at the solid/liquid interface. We extend the Navier-de Gennes description using one additional parameter, namely the density of physically adsorbed chains per unit surface. The resulting formulation is found to be in excellent agreement with the experimental observations.