Controllable Superlubricity of Ricinoleic Acid/Tungsten-Doped Amorphous Carbon Coating Composite System via Water Content

Carbon-based coatings combined with ricinoleic acid exhibit exceptional lubrication and macroscale superlubricity, yet the influence of the water content remains insufficiently explored. In this paper, a tungsten-doped amorphous carbon coating/ricinoleic acid composite system was prepared, and superlubricity was achieved by controlling the water content in ricinoleic acid. When the water content is 13.89 wt %, the friction coefficient of the solid-liquid system is approximately 0.005. This phenomenon is attributed to the formation of a -(CH₂-CH₂)_<i>n</i>- passivation layer during the sliding process. Based on this passivation layer, a hydrogen bond layer is formed from ricinoleic acid-water and the decomposition products of ricinoleic acid containing -OH groups. This hydrogen bond layer is strong enough to withstand normal loads, effectively preventing contact between solid surfaces.