Mushroom-Shaped Micropillars for Robust Nonwetting Surface by Electrohydrodynamic Structuring Technique

Mushroom-shaped micropillars (MSMPs) have a unique microscopic shape that is suitable to produce a highly robust nonwetting surface. This commercially important property is possible thanks to the specific overhang shape, which has a larger tip diameter than the shaft below. We fabricated such a textured surface using poly(methyl methacrylate) (PMMA) via electrohydrodynamic structuring technique. The method combines hot embossing, electrically induced growth, and electrowetting. Even though PMMA itself is hydrophilic (the intrinsic contact angle is 82°), its modified surface is hydrophobic with an apparent contact angle of 152°. We also studied the robustness of the nonwetting surface by comparing the difference between the static contact angles before and after the samples had been submerged in water. Our results show that only the surface structured with the 43-μm tip-diameter MSMPs (the largest size) can successfully maintain its highly nonwetting property. Because of the large fabrication potential of the MSMPs with a large tip diameter, the described surface structuring technique is a promising candidate for the mass production of artificial and sufficiently robust nonwetting surfaces.