Wet adhesion is widely adopted in biological adhesion systems in nature, and it is beneficial to design new materials with desired properties based on the underlying physics of wet adhesion. The aim of this work is to develop a design criterion to regulate the wet adhesion. The effects of different contact shapes (flat and sphere) and morphologies of the substrate (smooth, microstructure and nanostructure) on the adhesion force are investigated. Combining with the theoretical models, the dominated factors in the separation process and isolating the viscous contributions from the capillary interactions are evaluated. The results demonstrate that the adhesion mechanisms depend significantly on the capillary numbers of the interstitial liquid and the contact geometry, and the ratio of capillary force to viscous force is a key to regulate the wet adhesion mechanism. These findings can not only explain some phenomena of wet adhesion to organisms, but also provide some inspirations to design new adhesion technology for robotic fingers that can grasp objects in wet environments.

中文翻译：

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生物湿粘附的基础机制：间隙液体和接触几何的耦合效应

湿粘附力在自然界的生物粘附系统中被广泛采用，并且基于湿粘附力的基本物理原理来设计具有所需特性的新材料是有益的。这项工作的目的是开发一种设计标准来调节湿附着力。研究了不同的接触形状（平面和球形）和基材的形态（光滑，微观结构和纳米结构）对粘附力的影响。结合理论模型，评估了分离过程中的主要因素，并从毛细管相互作用中分离出粘性贡献。结果表明，粘附机制在很大程度上取决于间隙液体的毛细管数和接触几何形状，毛细力与粘性力的比是调节湿黏附机理的关键。这些发现不仅可以解释某些湿生物粘附现象，而且还可以为设计可以在潮湿环境中抓住物体的机械手指新粘附技术提供启发。