Superhydrophobicity of Auxetic Metamaterials

Auxetic metamaterials defy conventional expectations by expanding laterally when subjected to strain. This unexpected characteristic arises from the arrangement of the lattice rather than the properties of individual solid elements, with the expansion occurring by increasing the space fraction. This behaviour offers a pathway for engineering superhydrophobic materials with distinct wetting properties, which, surprisingly, has not been explored until now. Our experimental models demonstrate the correlation between different states of strain and superhydrophobicity as the lattice structure transitions from an auxetic to a conventional (positive Poisson's ratio) configuration. Through manipulation of joint rotation under strain, we effectively convert membranes from conventional superhydrophobic materials, with positive Poisson's ratios, into auxetic superhydrophobic materials, featuring negative Poisson's ratios. This transformation sheds light on the interplay between structure and wetting control. Our findings emphasize how the counterintuitive behavior of auxetic metamaterials, when combined with superhydrophobicity, gives rise to exceptional wetting properties. By comprehending and leveraging this relationship, we pave the way for the design and advancement of novel self-cleaning surfaces, droplet transportation systems, droplet encapsulation techniques, and oil-water separation methods.