Enhancement of oil repellency on hyperbolic microarrays by compressive bending of elastomeric films

Abstract

Applying elastic deformation to modulate the microscale surface shapes of films is an efficient way to prepare samples with various geometric designs. Tensile stress can be applied by stretching films, and it can increase the pitches of line arrays or the diameters of pillar arrays on a film surface. However, it is difficult to apply lateral compressive stress to films because films buckle during compression. In this study, we exploit bending to apply lateral compressive stress to the surface of a film. To accomplish this, we use arrays of microhyperbolic pillars or lines that have inversely tapered shapes in the upper region and widened bottoms. By using deformation of elastomeric films and a subsequent replication process, we fabricate microhyperbolic structures with decreased pitches and increased pattern heights. In addition, the deformation of microarrays by compressive stress can enhance oil repellency by increasing the sharpness of the inversely tapered shapes. Using this concept, we demonstrate the enhancement of oil repellency on patterned surfaces prepared by compressive bending of microarrays. Furthermore, we provide selective oil repellency by modulating the compressive stress on a single line array. The concept of compressive bending can be applied widely to decrease the dimensions of arrays and modulate surface shapes for greater oil repellency.