| A liquid surface with non-constant curvature is unstable, as the Laplace pressure drives a flow that is mediated by the viscosity. We present the results of atomic force microscopy experiments on one of the simplest possible non-flat surfaces: stepped bilayer thin polymer films. In the first set of experiments, height profiles are measured as a function of time for a variety of molecular weights. Additionally, the dependence of the flow on the geometry of the sample is examined. To understand the experimental results, we derive expressions for the energy dissipation as a function of time and film geometry which are in agreement with the experiments. The results indicate the ideality of stepped bilayer polymer systems as a use for nanometric rheological probes, and provide a conceptual framework in a simple system with which to understand highly viscous surface tension driven flows. |
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