Silane Treatment of Diamond-Like Carbon: Improvement of Hydrophobicity, Oleophobicity, and Humidity Tolerance of Friction

Hydrophobicity and humidity tolerance of the low friction behavior of hydrogenated diamond-like carbon (H-DLC) were improved via surface modification using vapor-phase chemical reactions with organic silanes at 250–280 °C. Water and hexadecane contact angles increased after silane treatments. Unlike pristine H-DLC which loses ultra-low friction behavior as soon as relative humidity (RH) increases to a few percent, silane-treated H-DLC films maintained a low friction behavior (with a coefficient less than 0.08) up to 30 % RH. Elemental analysis of the transfer films accumulated on the balls after friction tests indicated that the silane molecules not only decorated the topmost surface of the H-DLC, but also penetrated into and reacted with the subsurface. Surface roughness, water adsorption behavior, and hardness measurements also showed that silane treatment affected the surface morphology and subsurface porosity of the H-DLC film.