Fabrication of highly transparent slippery surfaces with omniphobicity by an improved process using non-solvent-induced phase separation

A facile nanoscale phase separation method has been proposed for the fabrication of slippery liquid-infused porous surfaces (SLIPSs). This method, however, suffered from the fact that high transmittance was unable to be achieved because it was difficult to control the surface roughness, film thickness, and optical properties. Moreover, membrane prepared by this method exhibited a low surface roughness, and organic droplets stuck to the SLIPSs prepared in several conditions. In this work, an improved process emphasizing the fluorinated alkyl silane (FAS) modification of poly(vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) was developed for the fabrication of competent SLIPSs. By using an aminosilane and a fluorinated alkyl silane in the first and the second modification steps, respectively, the hydrophobicity of the copolymer was shown to be effectively enhanced. Much better and reproducible SLIPSs can then be fabricated by the extremely simple process using non-solvent-induced phase separation (NIPS) of PVDF-HFP/di-n-butyl phthalate (DBP) solutions. The as-fabricated SLIPSs exhibited extreme liquid repellency as signified by very low sliding angles (less than 4° for droplet volume of 5 μl) against seven pure liquids (water, pentadecane, nonane, octane, heptane, hexane, and pentane) with surface tension values ranging from 72.8 to 17.2 mN/m. Furthermore, high optical transmittance (average transmittance = 92.9%) of the self-standing omniphobic thin film may find its applications among others in self-cleaning solar cells with minor deterioration in their conversion efficiency.