Wetting Transitions on an Auxetic Metamaterial

Superhydrophobicity holds significant importance across various applications. Recently, we have showcased the potential of auxetic metamaterials in creating superhydrophobic materials that possess unique wetting properties. However, these desirable properties are lost when the liquid infiltrates the surface structure. Hence, it is crucial to comprehend the factors governing droplet penetration in order to advance wetting control. In this study, we employ a surface energy argument to identify the critical elements that influence droplet suspension and penetration on an auxetic bowtie/honeycomb lattice structure. We develop a comprehensive physical model that represents different states of strain, ranging from auxetic to conventional lattices, while considering the variation in liquid surface tension using water/ethanol mixtures. By investigating the interplay between surface energy and lattice structure, we gain valuable insights into the conditions required for droplet suspension and penetration. Moreover, we identify a simple touch test that enables the distinction between the different wetting states (suspended versus penetrating), providing a practical and efficient method for characterization.