Friction-induced lubricating nanocoatings of main-chain thermotropic liquid crystalline polymer

Abstract The main-chain thermotropic liquid crystalline polymer (LCP) has been reported to be able to simultaneously lower friction coefficient and wear rate when introduced into poly (vinylidene fluoride) (PVDF) as the lubricant. In this investigation, we aim to obtain some insight into the lubricating mechanism of LCP. Through atomic force microscopy (AFM) and Raman spectroscopy, friction-induced in-situ nanocoatings of LCP are observed on friction PVDF domains, which arises from increasing surface temperatures and high shear thinning properties of LCP. Consequently, LCP nanocoatings obviously enhance microscopic hardness of friction PVDF domains. In other words, LCP nanocoatings could be treated as a type of protective lubricant to prevent the direct contact between counterface and PVDF domains, promote wear resistance and lower friction coefficient. To our best knowledge, such an interesting lubricating mechanism is rarely reported. Overall, this investigation not only proposes the novel lubricating mechanism of LCP, but also provides support for further tribological applications in the polymeric systems.