Slippage and Nanorheology of Thin Liquid Polymer Films

TL;DR

This study investigates how the boundary conditions at the solid/liquid interface influence the slip and rheology of thin polymer films, providing experimental data that support recent theoretical models on confined polymer dynamics.

Contribution

It offers new experimental insights into the boundary conditions affecting polymer slip and rheology in thin films, especially considering the role of chain length and entanglements.

Findings

Inter-chain entanglements near the interface govern slip behavior.

Polymer chain length influences boundary conditions and slip.

Experimental data corroborate recent theoretical models.

Abstract

Thin liquid films on surfaces are part of our everyday life, they serve e.g. as coatings or lubricants. The stability of a thin layer is governed by interfacial forces, described by the effective interface potential, and has been subject of many studies in the last decades. In recent years, the dynamics of thin liquid films came into focus since results on the reduction of the glass transition temperature raised new questions on the behavior of especially polymeric liquids in confined geometries. The new focus was fired by theoretical models that proposed significant implication of the boundary condition at the solid/liquid interface on the dynamics of dewetting and the form of a liquid front. Our study reflects these recent developments and adds new experimental data to corroborate the theoretical models. To probe the solid/liquid boundary condition experimentally, different ways are possible, each bearing advantages and disadvantages, which will be discussed. Studying liquid flow on a variety of different substrates entails a view on the direct implications of the substrate, the experimental focus of this study is the variation of the polymer chain length: The results demonstrate that inter-chain entanglements and in particular their density close to the interface, originating from non-bulk conformations, govern liquid slip of a polymer.