Super water- and oil-repellent surfaces resulting from fractal structure

Super water- and oil-repellent surfaces have been made utilizing the fracta l structure of the solid surfaces. Super water-repellent surfaces showing a contact angle of 160 degrees for water droplets have been made of anodical ly oxidized aluminum surfaces treated with hydrophobic surface coupling age nt (1H, 1H,2H,2H-perfluorooctyltrichlorosilane). The fractal dimension of t his surface was evaluated to be 2.19 by box counting fractal analysis. The anodically oxidized aluminum surface itself was superwettable for water lan d also other solvents), and the surface hydrophobized with the surface coup ling agent was altered to a super water-repellent surface. The super oil-re pellent surfaces are also prepared by treating the same aluminum surface wi th fluorinated monoalkyl phosphates (1H,1H,2H,2H-perfluorodecyl- and -perfl uorododecyl-phosphate). A rapeseed oil droplet having a surface tension of similar to 35 mN/m rolls around on the surface without attaching. The conta ct angle of the ;rapeseed oil on the super oil-repellent surface was 150 de grees, Most of the oils having a surface tension greater than 23 mN/m show greater contact angle than 120 degrees on the super-oil-repellent surfaces. The critical surface tension, gamma(c), was estimated to be 14.8 mN/m from the Zisman plot of the contact angles on the hat surface treated with 1H,1 H,2H,2H-perfluorododecyl phosphate, This value is between the gamma(c) of T eflon (18.5 mN/m) and that of -CF3 group (similar to 6 mN/m). (C) 1998 Acad emic Press.