Influence of surface roughness on water- and oil-repellent surfaces coated with nanoparticles

Various rough surfaces coated with titanium oxide nanoparticles and perfluoroalkyl methacrylic copolymer were conducted to explore the influence of surface roughness on the performance of water- and oil-repellence. Surface characteristics determined from nitrogen physisorption at -196 degreesC showed that the surface area and pore volume increased significantly with the extent of nanoparticle ratio, indicating an increase of surface roughness. Due to the surface nanocoating, the maximum contact angles of water and ethylene glycol (EG) droplets increased up to 56 and 48%, respectively, e.g. from 105degrees to 164degrees for water droplets and from 96degrees to 144degrees for EG droplets. The excellent water- and oil-repellence of the prepared surfaces was ascribed to this increase of surface roughness and fluorinated-contained surface. Compared with Wenzel model, the Cassie model yielded a fairly good fit to the simulation of contact angle with surface roughness. However, a derivation of 3degrees-10degrees at higher roughness still existed. This phenomenon was very likely due to the surface heterogeneity with different pore size distributions of the fractal surfaces. In this case, it was unfavorable for super repellency from rough surface with larger mesopore fraction because of its capillary condensation, reflecting that micropore provided more air resistance against wettability. (C) 2004 Elsevier B.V. All rights reserved.