Hydrophobic Coatings Obtained in Atmospheric Pressure Plasma

Plasma polymerization at atmospheric pressure is used to obtain stable hydrophobic coatings onto various substrates. Plasma is generated in a dielectric barrier discharge configuration using a mixture of helium gas and styrene vapors. The discharge is characterized by means of electrical measurements and optical emission spectroscopy. Since the styrene vapors introduced in plasma provide a significant decrease of the discharge current, we established the optimum parameters (voltage waveform, gap length, and gas flow rates) for plasma polymerization, assuring a maximum discharge current. The plasma-polymerized films (polystyrene), deposited onto the glass or silicon substrates, are analyzed by contact angle measurements, ellipsometry, IR spectroscopy, and atomic force microscopy (AFM). The film thickness is measured by light interferometry and confirmed by AFM analysis. The water contact angles are higher than 130deg, proving the hydrophobic characteristics of the film, and the refractive index is around 1.5, corresponding to the values of commercial polystyrene.