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R&D Profile: Effects of Surface Texture and Chemistry on Surface Hydrophobicity and Oleophobicity - Kock-Yee Law*, Hong Zhao and Varun Sambhy, Xerox Research Center, US

Inspired by nature (Lotus effect) and its “self cleaning” effect, scientists at Xerox Research Center Webster have launched a systematic investigation to explore if micro/nanostructured surfaces can enable easy-clean, self-clean and offset free feature for future printing engines.

Overview courtesy of K.Y. Law, Xerox Research Center, US

The surface textures studied in this work were created by the conventional photolithographic technique on Silicon wafer, followed by chemical modification of the patterned surface with an appropriate nano conformal coating. The researchers observed very high water and oil repellency for a fluorinated silane treated surface comprising of ~ 3 μm diameter pillars ~ 7 μm in height with an inter-pillar distance of ~ 6 μm. The surface is both superhydrophobic and superoleophobic with static contact angles approaching ~ 160° for both water and hexadecane. [Figure] The attainment of superolepohobicity was attributed to both surface texturing and surface fluorination.

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Figure (a) SEM micrograph of textured surface and (b) contact angle data of the surfaces.

Initial results on the effects of chemical modification and pillar geometry on the surfaces property reveal that the textured surfaces will be superhydrophobic when hydrophobic coatings are used to modify the surface. On the other hand, the oleophobicity of the textured surfaces varies, ranging from super wetting to superoleophobic with hexadecane, depending on the oleophobicity of the surface coating. High magnification SEM analysis revealed that the side walls of the pillars have a submicron wavy structure due to the etching process. Superoleophobicity was not attained when the side walls in the pillars are straight and smooth (comparable patterns). The surface is still superhydrophobic (water CA 153°), but its oleophobicity reduces substantially, to a hexadecane CA of ~ 103°. On the other hand, the textured surface remains superoleophobic if each straight wall pillar has a re-entrant structure.

To date, surfaces of varying hydrophobicity and oleophobicity have been created and the Xerox scientists will use these surfaces to investigate their interactions with various Xerox imaging materials. Through fundamental studies, the Xerox scientists hope to design surfaces with radically improvement in printing performance.

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