Controlling Marangoni induced instabilities in spin-cast polymer films: how to prepare uniform films

TL;DR

This study investigates how temperature influences Marangoni-induced surface instabilities during spin coating of polymer films, demonstrating that lowering temperature can produce more uniform films by suppressing these instabilities.

Contribution

The paper identifies temperature as a key factor affecting Marangoni instabilities in spin coating and shows how adjusting temperature can control film uniformity.

Findings

Surface instabilities depend on temperature.

Wavelength and amplitude of patterns increase with temperature.

Lowering temperature prevents non-uniformities.

Abstract

In both research and industrial settings spin coating is extensively used to prepare highly uniform thin polymer films. However, under certain conditions, spin coating results in films with non-uniform surface morphologies. Although the spin coating process has been extensively studied, the origin of these morphologies is not fully understood and the formation of non-uniform spincast films remains a practical problem. Here we report on experiments demonstrating that the formation of surface instabilities during spin coating is dependent on temperature. Our results suggest that non-uniform spincast films form as a result of the Marangoni effect, which describes flow due to surface tension gradients. We find that both the wavelength and amplitude of the pattern increase with temperature. Finally, and most important from a practical viewpoint, the non-uniformities in the film thickness can be entirely avoided simply by lowering the spin coating temperature.