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.

粘性液体通常在固体壁上表现出流动滑移。流动滑移的发生对液体传输和由此产生的能量耗散有很大影响，这对于许多应用至关重要。很自然地预期会发生滑移以减少耗散。然而，（i）密度波动如何受到壁的存在的影响以及（ii）通过形成气体层如何发生滑移仍然难以捉摸。在这里，我们报告了这些基本问题的可能答案：（i）即使在静止状态，无论壁的性质如何，密度波动在壁附近本质上都会增强，并且（ii）粘度的密度依赖性会破坏系统的稳定性在剪切流下形成气层。我们的剪切诱导气相形成场景为液体流动的壁滑移提供了自然的物理解释，涵盖了从微观（纳米）到宏观（微米）尺度的滑移长度。