Effects of Surface Texture and Chemistry on Surface Hydrophobicity and Oleophobicity
K-Y Law, H. Zhao, V. Sambhy
Xerox Corporation, US
Keywords: superhydrophobicity, superoleophobicity, nanostructured coating
Abstract:The effects of surface texture and chemical modification on the hydrophobicity and oleophobicity of the resulting surfaces have been systematically investigated. The surface textures were created by the conventional photolithographic technique on Silicon wafer. This was followed by chemical modification of the patterned surface with a fluorinated silane layer or a hydrocarbon self assembled layer. We observed very high water and oil repellency for a fluorinated silane treated surface comprising of ~ 3 micron diameter pillars ~ 7 micron tall with a ~ 3 micronm inter-pillar distance. The surface is both superhydrophobic and superoleophobic with static contact angles (CA) approaching ~ 160 degree; for both water and hexadecane. High magnification analysis revealed that the side walls of the pillars have a submicron wavy structure due to the etching process. Superoleophobicity was not achieved for a comparable patterned surface when the side walls are straight and smooth. The surface is still superhydrophobic (water CA 153 degree), but its oleophobicity reduces substantially, to a hexadecane CA of ~ 103 degree;. The achieved superoleophobicity in the earlier surface may be attributable to the “dual roughness scale” introduced in the waviness structure or to the so-called re-entrant angle at the air-liquid interface. Further work is in progress to differentiate these two possibilities. In addition to the geometry of the pillar, initial results on the effects of surface chemistry and pillar size & patterning on surface hydrophobicity and oleophobicity will also be reported and discussed.