Simulations of Thin Polymer Films on Flat and Curved Substrates

TL;DR

This study uses molecular dynamics simulations to explore how substrate curvature affects the shape and conformation of polymer thin films, revealing effects like chain stretching and partial dewetting.

Contribution

It provides new insights into the influence of substrate topography on polymer film morphology through combined simulation and analytic modeling.

Findings

Polymer chains stretch or compress depending on substrate curvature.

Partial dewetting occurs near high curvature regions for thin films.

Thicker films tend to flatten and conform to substrate shape.

Abstract

We report molecular dynamics simulation results on the equilibrium properties of polymer thin films adsorbed onto flat and curved substrates. We first systematically determine the contact angle of polymer droplets on flat substrates as a function of the substrate-monomer adsorption strength and degree of polymerization. Focussing on the fully wetted regime, we then investigate the effect of the substrate's topography on the polymer film configuration by using substrates with varying mean curvature. We find that polymer chains close to the substrate are significantly stretched (compressed) in regions of high negative (positive) mean curvature. Further, we find partial dewetting near regions of high mean curvature for thin polymer films. For thicker films, the polymers fully cover the substrate and the shape of the liquid-vapor interface largely follows the shape of the substrate. As the film thickness is increased further, the liquid-vapor interface becomes completely flat. These simulation results are corroborated by analytic calculations using a simplified continuum model that treats the adsorbed polymers as an incompressible medium. Our findings show how the substrate topography influences the conformation of individual chains as well as the shape of the entire film.