Dynamic wetting failure in shear-thinning and shear-thickening liquids is examined in this paper. Flow visualization experiments using a curtain-coating geometry suggest that shear thinning postpones the onset of wetting failure and the resulting air entrainment. To advance the fundamental understanding of the underlying physical mechanisms, a hydrodynamic model consisting of liquid displacing air in a rectangular channel in the absence of inertia is developed. Both shear thinning and shear thickening are considered by using Carreau-type models to describe the liquid rheology. Steady-state solutions are calculated using the Galerkin finite-element method and the critical capillary number where wetting failure occurs is identified. Shear thinning is found to postpone the onset of wetting failure whereas shear thickening is found to promote it. The underlying mechanism involves thickening/thinning of the air film as a consequence of shear thinning/thickening of the liquid and the tangential stress balance. The results can be interpreted in terms of an effective viscosity, and demonstrate that similar physical mechanisms govern dynamic wetting failure in Newtonian, shear-thinning and shear-thickening liquids.

中文翻译：

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剪切稀化和剪切稠化液体中的动态润湿破坏

本文研究了剪切稀化和剪切稠化液体中的动态润湿失效。使用幕帘涂层几何形状的流动可视化实验表明，剪切稀化推迟了润湿失效的发生和由此产生的空气夹带。为了促进对潜在物理机制的基本理解，开发了一个流体动力学模型，该模型由在没有惯性的情况下在矩形通道中置换空气的液体组成。通过使用 Carreau 型模型来描述液体流变，同时考虑了剪切稀化和剪切增稠。使用 Galerkin 有限元方法计算稳态解，并确定发生润湿失效的临界毛细管数。发现剪切稀化可推迟润湿破坏的发生，而发现剪切增稠可促进润湿破坏的发生。潜在的机制涉及由于液体的剪切变稀/变稠和切向应力平衡而导致的空气膜变厚/变薄。结果可以解释为有效粘度，并证明类似的物理机制控制牛顿流体、剪切稀化和剪切增稠液体中的动态润湿失效。