Robust hydrophobic surfaces with various micropillar arrays

Abstract

In the present study, we design, fabricate and characterize robust hydrophobic surfaces on which four different shapes (rectangle, circle, triangle and cross) of a micropillar array are patterned. Various micropillar arrays are designed to give rise to the same Wenzel and Cassie contact angles (CAs) of the surfaces through changes in the shape and size of the micropillar and the spacing between adjacent micropillars. The designed surfaces are fabricated using polydimethylsiloxane (PDMS) replica molding with photolithographically manufactured SU-8 masters. The hydrophobicities of the various PDMS surfaces are evaluated through theoretical and experimental measurements of the water CAs. The theoretical and experimental CAs are strongly correlated to each other, as expected. The generalization of the suggested design rule was carried out by introducing effective parameters of square-arranged micropillar arrays. The apparent contact angle of the robust hydrophobic surface monotonically increases as the top surface area decreases for a given perimeter and height.