(529d) Photochemical Approach to Achieve Simultaneous Oleophobicity/Hydrophilicity

The simultaneously hydrophilic/oleophobic surfaces have important applications in oil-water separating, detergent-free cleaning and anti-fogging. However, this type of surface was rarely reported since most of the solid surfaces are more wettable to oil than to water.   Our previous studies showed that the simultaneous hydrophilicity/oleophobicity could be achieved by coating the nanometer-thick perfluorinated polymer with polar endgroups on a hydrophilic substrate. In that case, polymer molecules form a nanometer-thick network on the solid surface with perfluorinated backbones on top. Both water and oil molecules tend to penetrate the network to approach the equilibrium state since the solid surface has high surface energy. Because water molecules are much smaller than oil molecules, they penetrate the network much faster. As a result, in a contact angle test conducted in short time period, the measured water contact angle is lower than the oil contact angle. However, the perfluorinated polymers with polar endgroups are too expensive for real-life applications. In the current study, we have investigated the photochemical approach to achieve simultaneous hydrophilicity/oleophobicity for perfluorinated polymers without polar endgroups. The contact angle testing showed that UV irradiation of nanometer-thick perfluorinated polymers without polar endgroups on a silica substrate has resulted in the simultaneous oleophobicity/hydrophilicity. The ellipsometry and X-ray photoelectron spectroscopy (XPS) results indicated that UV irradiation causes the covalent bonding between the polymer backbone and the silica substrate, which promotes the formation of the polymer network and thus render the surface simultaneously hydrophilic/oleophobic.