How moisture driven mechanochemistry stabilizes transfer film adhesion and cohesion in ultralow wear PTFE composite

Prior studies suggest mechanical interlocking, preferential adhesion of polar polymers , and PTFE tribochemistry all contribute to the wear reduction in polar polymer-filled PTFE composites; whereas their relations remain poorly understood. This study aims to decouple the relevant mechanisms by investigating wear and tribofilm environmental sensitivities of a 5 wt% polyamide-imide (PAI) filled PTFE composite. The results highlight (1) strong correlation between a carboxylate-salt-rich transfer film and ultralow wear, and (2) a tribochemical interface gradient that discourages transfer film removal. We proposed that PTFE tribochemistry induces ultralow wear by significantly increasing (1) transfer film adhesion through a virtuous cycle of tribochemical accumulation and wear reduction and (2) transfer film cohesion by promoting a surface energy interface gradient beneficial to low wear.