Deposition of superhydrophobic coatings on glass substrates from hexamethyldisiloxane using a kHz-powered plasma jet

Abstract

Deposition of superhydrophobic coatings on glass substrates from hexamethyldisiloxane (HMDSO) precursor using an argon plasma jet at a relatively low power frequency (11.5 kHz) was studied. The coating hydrophobicity was first found to be strongly dependent on the gaseous shield. Nitrogen (N2) rather than inert gases (argon, Ar, and helium, He) had an excellent shielding effect against the interference of ambient air on the plasma jet. The evolution of water contact angle (WCA) of the prepared coating was investigated upon the variations of the operating parameters, such as N2/Ar ratio, HMDSO concentration, deposition time and nozzle-to-substrate distance. Generally, the measured WCA gradually increased with increasing the values of these parameters and then leveled off at some specific values, except for the nozzle-to-substrate distance. The wettability of glass was completely switched from hydrophilicity to superhydrophobicity with the WCA reaching 168° and the sliding angle of about 3° at optimum conditions. The surface morphology analyses by scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed that the prepared coating had a very high surface roughness and micro-nano structure, which intensely promoted the water repellence property. The chemical examination by X-ray photoelectron spectroscopy (XPS) clearly showed the shielding effect on the surface chemical composition of the coating. N2 shield preserved a high carbon content (in CH3 groups) from the precursor, while minimizing the incorporation of oxygen into the coating surface. Also, it was found that O (from O and OH radicals) has replaced C to form silica-like coating in case of without shielding gas or with Ar and He shields.