Solvent resistant superhydrophobic films from self-emulsifying carnauba wax–alcohol emulsions

Abstract

By dispersing molten carnauba wax in warm isopropyl alcohol or ethanol with subsequent mild ultrasonic mixing, highly stable surfactant-free natural wax-in-alcohol emulsions were prepared for the first time. These emulsions can easily suspend hydrophobic colloidal organics or solids. We demonstrate fabrication of superhydrophobic films from sub-micron polytetrafluoroethylene (PTFE) particle-dispersed emulsions by a simple drop and/or spray casting procedure and subsequent thermal annealing above the melting point of carnauba wax. We investigate effect of wax and Teflon concentration and thermal annealing on the degree of superhydrophobicity. Moreover, the films display superior resistance to solvent etching against aggressive solvents such as chloroform, toluene, acetone and alcohols upon immersion into such solvent baths for one hour. Composite films remain superhydrophobic after solvents evaporate from their surfaces following their removal from the solvent baths. Moreover, detailed contact angle hysteresis measurements revealed that solvent bath immersion does not downgrade “self-cleaning” superhydrophobicity to “sticky” superhydrophobicity.