很多天然生物材料利用其表面浸润性质实现特有的生物功能。随着科学技术的发展，生物启发的超疏水浸润材料在人们的生产生活中扮演越发重要的角色，例如，具有自清洁、抗结露、抗结冰等浸润功能的先进材料已在建筑、纺织、能源等领域获得重要应用。目前，固体表面浸润研究已成为材料、力学、化学等学科的一个前沿课题。本文以固体材料表面的微纳米几何结构为中心，研究固体表面浸润的几何学分类方法与超疏水浸润状态的稳定性，主要研究内容如下：首先，基于对天然和人工超疏水材料的表面形貌的总结，提出了一种对多级表面结构在微、纳米尺度上进行几何维度分类方法。利用该分类方法，同时参考已有的超疏水材料研究素材，将材料的表面功能与几何形貌联系在一起，形成几何结构–表面功能图谱。利用材料表面结构的几何维度作为连接的桥梁，可以方便地建立起仿生表面功能、几何形貌与实验制备方法之间的逻辑纽带。基于热力学能量方法，建立了用于分析具有平面型、空间型表面微结构的超疏水材料表面上Cassie–Baxter（CB） 浸润状态的理论框架。对于具有任意母线轮廓的微结构，推导了其上CB浸润状态的平衡和稳定性准则，给出了求解CB浸润状态失效时临界压强的一般方法，并得到了具有直母线或圆弧母线表面结构的临界压强的显式表达。分别从几何和化学角度，提出了提高微米尺度的CB浸润状态的稳定性的方法。通过考虑线张力效应，采用能量方法研究了纳米表面结构上浸润状态的力学性质，并为纳米颗粒漂浮实验所验证。基于该方法分析了CB浸润状态的平衡、稳定性。结果表明，线张力的存在可能会引入能量势垒，约束三相线接触位置在固体壁面上的分布，并改变浸润的平衡特性。本文所提出的理论模型可以很好地预测临界压强相对于线张力变化的上下限以及变化率。此外，提出了增强纳米尺度CB浸润状态的稳定性的方法。最后，通过对具有微柱阵列表面结构的超疏水材料进行水滴压入实验，测量了发生CB–Wenzel浸润转变时的临界压力、变形信息。结果显示，微柱壁面的接触角平均比固体材料的本征接触角大约30°，而以往理论大都采用两者相等的近似假设，该假设将会导致理论预测的临界压强和临界力过于保守。本文建议在本征接触角上添加一个描述接触角偏差效应的常量，从而提高理论预测的精度。
Many biological materials achieve their unique functions through wetting properties. With the development of technology, bioinspired materials with superhydrophobic-related wetting functions play an ever increasing significant role in our daily life. For example, advanced functional materials with wetting properties such as self-cleaning, anti-fogging, and anti-icing have found important applications in the fields of architecture, textile, and energy. Currently, the research of surface wetting of solid materials has become a frontier in the fields of materials science, chemistry and mechanics. Focusing on the micro/nano-structures on solid surfaces, this dissertation studies the geometrical classification of wetting on solid surfaces and the stability property of the superhydrophobic state. The main results are as follows:Firstly, based on the observation and organization of various kinds of biological and artificial materials with superhydrophobicity, a dimensional classification method is proposed to categorize the hierarchical surface structures at the micro and nano scales. Using this classification method, one can refer to the known biological tissues, and conveniently correlate the surface function of materials with their surface morphologies, and then make the morphology–function map. By using this dimensionality classification as a bridge, one can readily find the relation among the bio-inspired function demand, the surface geometry and the fabrication method.Using an energy approach, a theoretical framework to analyze Cassie–Baxter (CB) wetting states is established for solid surfaces with either planar or spatial microstructures. Then, we provide the equilibrium and stability criteria of wetting states on microstructures with arbitrary generatrix, and propose a generic method to calculate the critical pressure when the CB state collapses. For a few representative microstructures with a straight or circular generatrix, explicit solutions of critical pressure are derived. In addition, some strategies are proposed to design surface structures with stable CB wetting states from the viewpoints of geometry and chemistry.By considering the effect of line tension, the wetting behavior at the nanoscale is analyzed by using the energy method. After the theoretical framwork is verified by the particle-floating experiments, we further study the equilibrium and stability properties of CB wetting state. It is found that the line tension may introduce an energy barrier, restrict the location of the three-phase contact line on the structural surface, and influence the equilibrium property. Our model can well predict the upper/lower limits and variation rate of the critical pressure with respect to line tension. In addition, some strategies are proposed to increase the CB stability at the nanoscale.Finally, by conducting water droplet compression test on periodic micropillar arrays, we experimentally measure the force and displacement information at the CB to Wenzel wetting transition. Our results show that the contact angle on micropillar sidewalls is averagely about 30° larger than the intrinsic contact angle. Most previous theories use the approximation that these two values are equal to each other, leading to a conservative prediction of critical pressure and critical force compared with the real values. To improve the analysis accuracy of the wetting transition state, we propose that the intrinsic contact angle used in the models can be simply modified by adding a constant describing the contact-angle-difference effect.
