Effects of calcination temperature on the microstructure and wetting behavior of superhydrophobic polydimethylsiloxane/silica coating

The superhydrophobic coating was prepared through spraying the mixture of polydimethylsiloxane (PDMS) and hydrophobic nanosilica (SiO2) on the slide glass. The surface of the as-prepared PDMS/SiO2 coating showed hierarchical roughness with a water contact angle (WCA) of 153°. The resultant superhydrophobic PDMS/SiO2 coating was subsequently calcined in a muffle furnace under air atmosphere and the effects of calcination temperature on the microstructure, component, transmittance, and wetting behavior of superhydrophobic PDMS/SiO2 coating were systematically investigated. With the increase in calcination temperature from 100 °C to 400 °C, the superhydrophobic PDMS/SiO2 coating became transparent with the visible light transmittance increasing from 40% to 80%, which was ascribed to the decomposition of PDMS and the rearrangement of the hydrophobic SiO2 particles. However, when the calcination temperature was over 500 °C, the wetting behavior of the coating changed from superhydrophobicity to superhydrophilicity with a WCA of nearly 0°, owing to the replacement of hydrophobic Si–CH3 groups with hydrophilic groups of Si–OH. Finally, the calcination mechanism of the superhydrophobic PDMS/SiO2 composite coating is proposed, which has guiding significance for the study of other composite coatings.