Preliminary Study of the Superlubricity Behavior of Polyimide-Induced Liquid Crystal Alignment

We have studied the friction behavior based on liquid crystal (LC) alignment of a unique tribological system composed of a nematic LC and polyimide (PI). The LC was used as a lubricant and a tribological factor with molecular alignment ability. PI was used as both a rubbing pair part and a LC alignment agent. The LCs used as lubricants included the single LC 5CB and the mixed LCs 5CB–2UTPP3 and 3PEP5–3UTPP4. The PI used as the friction pair was 6FDA-ODA PI, and its counterpart was GCr15 steel. For this system, it was found that under the premise that the nematic phase temperature range of the selected LC meets the operating temperature of the friction test at a suitable ambient temperature, the operating speed and load are controlled to maintain a stable lubricating film thickness between the friction pairs during operation of the system. Moreover, by avoiding excessive or insufficient friction heat generated by the running speed being too high or too low to change the phase state of the LC, with the anchoring energy between the PI and the LC, the LC molecules will align in the rubbing direction, that is, they will arrange parallel to each other along the grooves, which can contribute to achieve superlubricity behavior.