Kurotani Yuji, Tanaka Hajime
Department of Fundamental Engineering, Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan.
Sci Adv. 2020 Mar 27;6(13):eaaz0504. doi: 10.1126/sciadv.aaz0504. eCollection 2020 Mar.
Viscous liquids often exhibit flow slippage on solid walls. The occurrence of flow slippage has a large impact on the liquid transport and the resulting energy dissipation, which are crucial for many applications. It is natural to expect that slippage takes place to reduce the dissipation. However, (i) how the density fluctuation is affected by the presence of the wall and (ii) how slippage takes place through forming a gas layer remained elusive. Here, we report possible answers to these fundamental questions: (i) Density fluctuation is intrinsically enhanced near the wall even in a quiescent state irrespective of the property of wall, and (ii) it is the density dependence of the viscosity that destabilizes the system toward gas-layer formation under shear flow. Our scenario of shear-induced gas-phase formation provides a natural physical explanation for wall slippage of liquid flow, covering the slip length ranging from a microscopic (nanometers) to macroscopic (micrometers) scale.
粘性液体在固体壁面上常常出现流动滑移现象。流动滑移的发生对液体传输以及由此产生的能量耗散有很大影响，而这对于许多应用来说至关重要。人们自然会期望发生滑移以减少耗散。然而，（i）壁面的存在如何影响密度波动，以及（ii）滑移如何通过形成气体层而发生，这些问题仍然不清楚。在此，我们报告了这些基本问题的可能答案：（i）即使在静止状态下，壁面附近的密度波动本质上也会增强，而与壁面的性质无关；（ii）正是粘度的密度依赖性使得系统在剪切流下朝着气体层形成的方向变得不稳定。我们提出的剪切诱导气相形成的设想为液体流动的壁面滑移提供了一种自然的物理解释，涵盖了从微观（纳米）到宏观（微米）尺度的滑移长度范围。
