Department of Physics and Astronomy, McMaster University, Hamilton, Canada.
Phys Rev Lett. 2012 Sep 21;109(12):128303. doi: 10.1103/PhysRevLett.109.128303. Epub 2012 Sep 18.
The surface of a thin liquid film with a 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 thin polymer film with a step. 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.
具有非恒定曲率的薄液膜表面是不稳定的，因为拉普拉斯压力会驱动由粘度介导的流动。我们介绍了最简单的可变曲率表面之一的实验结果：具有台阶的薄聚合物膜。针对各种分子量测量了高度轮廓随时间的变化。结果表明，轮廓的演化是自相似的。通过与薄膜方程的数值解进行比较，这种自相似性为毛细管速度提供了精确的测量。我们还推导出了一个主表达式，用于表示作为材料特性和膜几何形状函数的过剩自由能的时间依赖性。实验和理论非常吻合，表明了台阶聚合物膜在阐明纳米尺度流变性质方面的有效性。
