The Induced Orientation of Hydroxypropyl Methylcellulose Coating for Ultralow Wear

This study investigated the frictional properties of HPMC under different load and concentration conditions through friction experiments and surface characterization. The study aimed to explore and reveal the influence of load and concentration on the frictional properties of HPMC, as well as its anti-wear mechanism. The results of the study indicated that under the same solution concentration, the effect of load on the friction coefficient of HPMC was not significant. Specifically, for samples with low concentration (C-0.2), the wear ratio of HPMC under a 4 N load (1.01 x 10-11 mm3N-1m-1) was significantly lower than the wear ratio under a 2 N load (1.71 x 10-10 mm3N-1m-1). The orientation-driven formation of graphite-like carbon nanosheets, initiated by the decomposition of HPMC short chains, created a tribofilm-containing organic-chain mixed nanosheet on the sliding contact surface, which prevented direct contact between the upper and lower friction pairs. This achieved the anti-wear mechanism of two-body wear (tribo-film of an mDLC-coated ball and tribo-film of a GLC-coated Si wafer), ultimately leading to a state of ultra-low wear at the interface. The excellent anti-wear performance of HPMC suggests its potential as a candidate for the next generation of environmentally friendly bio-based solid lubricants.