Robust Superomniphobic Micro-Hyperbola Structures Formed by Capillary Wrapping of a Photocurable Liquid around Micropillars

Superomniphobic surfaces inspired by nature have been studied for decades. Recently, the development of liquid-repelling surfaces has moved from the fabrication of artificial structures to real applications that address friction associated with clothes, paper, and skin. To have superoleophobicity, re-entrant structures such as mushrooms or inverse trapezoids have been suggested. However they can be mechanically fragile, especially under shear stress, because the bottom region is narrow. Here, a facile method to obtain new re-entrant structures is proposed, namely, micro-hyperbola structures, by wetting a photocurable viscous liquid around micropillars by capillary force. It is demonstrated that the formation of the hyperbola structures depends on the spacing ratio between micropillars, and the formation mechanism is explained with a simple model. The micro-hyperbola structure demonstrates robust omniphobicity even after rubbing and abrasion tests. The advantage of the wide fabrication range and the robust superoleophobicity of micro-hyperbola structures enable the uses in practical superomniphobic applications that undergo shear forces.