Deposition of stable hydrophobic coatings with in-line CH₄ atmospheric rf plasma

A CH₄ atmospheric rf plasma treatment process was demonstrated for hydrophobic treatments of various substrates including metallic and insulating surfaces as well as flat and rough surfaces. A stable rf glow plasma was generated over a 1 cm × 16 cm area using a cylindrical electrode geometry. A typical hydrophobic treatment speed was 5-10 cm min^-1. CH₄ plasma polymerization deposited a very smooth hydrocarbon layer composed of CH₂ and CH₃ groups. The inclusion of oxygenated species was less than 1%. On flat substrates, the water contact angle was ∼90°. On rough surfaces such as cotton, the contact angle reached up to 150°. Since this method does not require vacuum or any special venting systems, it will be suitable for in-line processing of a wide range of substrate materials.