The effect of pattern sizes on oleophobicity and superhydrophobicity of micropatterned surfaces

Abstract

In this study, cylindrical pillars with varying diameters between 10 μm to 100 μm, seperation distances between 5 μm to 10 μm, constant heights of 40 μm ± 2 and solid area fractions [fsCB(geo)] between 0.349 to 0.712 were prepared by deep reactive ion etching process and all surfaces were hydrophobized/oleophobized by coating with perfluoro-styrene (TM/S) random copolymer that was synthesized in CO2-expanded monomer. It was found that, oleophobic behaviors of the patterned surfaces were affected from the type of the hydrocarbon liquids used and with the increase of hydrocarbon liquid chain lengths cylindrical pillar surfaces exhibited more oleophobic behavior. Pattern sizes also affected both oil and water drop CA values however oil and water drops behaved oppositely on the pillar surfaces. Applicability of Cassie-Baxter equation on cylindrical pillar surfaces was also investigated and was found that CA values of both water and hydrocarbon liquids were not obeying Cassie-Baxter theory however in the case of hydrocarbon liquids deviations from the theory were much more larger.