Wetting of Metamaterial Surfaces

润湿在从喷墨印刷到防静电涂料和除草剂处理的许多不同应用中起着重要作用[1]。固体基底与气液界面的夹角（即接触角）是反映固体表面润湿性的主要参数之一。固体表面的超疏水性的特征在于水滴的非常大的接触角。如此大的接触角是通过向化学疏水的平坦固体表面添加结构来实现的-通常模仿天然表面，如荷叶[2]。在结构化表面上，液滴可以悬浮在表面特征上，并与固体形成更大的角度，如图1a所示。在这种情况下，液滴接触角取决于空气和固体的表面分数，并且增加空气分数会增加接触角。

Wetting plays a major role in many different applications from inkjet printing to antifouling coatings and herbicide treatment [1]. The angle between solid substrate and liquid-vapour interface (i.e. contact angle) is one of the main parameters to reflect the wettability of the solid surface. Superhydrophobicity of a solid surface is characterized by the very large contact angle of water droplets. Such large contact angles are achieved by adding a structure to the chemically hydrophobic, flat solid surface - often mimicking natural surfaces such as Lotus leaf [2]. On a structured surface, the droplet can suspend across the surface features and make a larger angle with the solid as can be seen in Fig. 1a. In such a case, the droplet contact angle depends on the surface fractions of air and solid, and increasing the air fraction increases the contact angle.