The surface of a thin liquid film with nonconstant curvature is unstable, as the Laplace pressure drives a flow mediated by viscosity. We present the results of experiments on one of the simplest variable curvature surfaces: a stepped polymer film. Height profiles are measured as a function of time for a variety of molecular weights. The evolution of the profiles is shown to be self-similar. This self-similarity offers a precise measurement of the capillary velocity by comparison with numerical solutions of the thin film equation. We also derive a master expression for the time dependence of the excess free energy as a function of the material properties and film geometry. The experiment and theory are in excellent agreement and indicate the effectiveness of stepped polymer films to elucidate nanoscale rheological properties.
@article{arxiv.1209.1228,
title = {Self-Similarity and Energy Dissipation in Stepped Polymer Films},
author = {Joshua D. McGraw and Thomas Salez and Oliver Bäumchen and Elie Raphaël and Kari Dalnoki-Veress},
journal= {arXiv preprint arXiv:1209.1228},
year = {2015}
}
Comments
5 pages, 4 figures, article accepted for publication in Physical Review Letters