Department of Experimental Physics, Saarland University, D-66041 Saarbrücken, Germany.
Phys Rev Lett. 2009 Dec 11;103(24):247801. doi: 10.1103/PhysRevLett.103.247801. Epub 2009 Dec 8.
Hydrodynamic boundary conditions play a crucial role in the flow dynamics of thin films and can be probed by the analysis of liquid front profiles. For long-chained polymer films it was reported that a deviation from a symmetric profile is a result of viscoelastic effects. In this Letter, however, evidence is given that merely a slip-boundary condition at the solid-liquid interface can lead to an asymmetric profile. Variation of molecular weight shows that slippage is directly linked to chain entanglements. We find a reduced entanglement density at the solid-liquid interface (factors 3 to 4), which stresses the importance of considering nonbulk polymer properties in the vicinity of an interface.
流体动力学边界条件在薄膜流动动力学中起着至关重要的作用，可以通过分析液体前缘轮廓来探测。对于长链聚合物薄膜，据报道，不对称轮廓是粘弹性效应的结果。然而，本研究给出的证据表明，固体-液体界面处的滑移边界条件仅会导致不对称轮廓。分子量的变化表明，滑移与链缠结直接相关。我们发现，固体-液体界面处的缠结密度降低（降低了 3 到 4 倍），这强调了在界面附近考虑非整体聚合物性质的重要性。
