Superhydrophobicity of Auxetic Metamaterials

TL;DR

This paper demonstrates that auxetic metamaterials with negative Poisson's ratio can be engineered to exhibit strain-dependent superhydrophobicity, enabling innovative applications in self-cleaning, droplet control, and separation technologies.

Contribution

It introduces a novel method of inducing superhydrophobicity in auxetic metamaterials through mechanical strain, linking structure deformation to surface wettability.

Findings

Superhydrophobicity varies with strain in auxetic structures.

Surface solid fraction decreases as lattice expands.

Experimental models confirm the strain-superhydrophobicity relationship.

Abstract

Superhydrophobic materials are often inspired by nature, whereas metamaterials are engineered to have properties not usually found in naturally occurring materials. In both cases, the key that unlocks their unique properties is structure. Here, we show that a negative Poisson's ratio (auxetic) mechanical metamaterial is capable of transforming into a unique type of superhydrophobic material. When stretched its surface has the counterintuitive property that it also expands in the orthogonal lateral direction. We model the change in the solid surface fraction as strain is applied and show it decreases as the space between solid elements of the auxetic lattice expands. This results in a unique dependence of the superhydrophobicity on strain. We construct experimental models illustrating the relationship between different states of strain and superhydrophobicity as the lattice structure transitions from an auxetic to a conventional (positive Poisson's ratio) one. The principles we have discovered offer a new approach to designing superhydrophobic materials for self-cleaning surfaces, droplet transportation, droplet encapsulation and oil-water separation.