Study On Mechanism Of Liquid Crystal Lubrication By Adding Flaky Self-lubricating Nanoparticles

Due to the outstanding anti-friction and anti-wear properties,liquid crystals are expected to become new lubricants.This thesis focused on further enhancing the lubricity of liquid crystals via selecting flaky self-lubricating nanoparticles as lubricity additives for liquid crystals.In order to study the lubricity of liquid crystals at room temperature,4-n-pentyl-4-cyanobiphenyl(5CB)is used as the basic lubricant.Graphene,which has high structural match with 5CB molecules,was selected as a lubricating additive to prepare graphene/5CB.Hexagonal boron nitride(h-BN),which has a lamellar nanostructure similar to graphene and has self-lubricating property,was selected as the second lubricating additive to prepare h-BN/5CB.The lubricating properties of these two lubricants were studied,and their lubrication mechanisms were analyzed respectively.The main contents of this study are as follows:The effects of graphene concentration,graphene size and test temperature on the lubrication performance of graphene/5CB were studied on a ball-on-plate tribotester.It was found that when the concentration of graphene with small size and few layer in graphene/5CB was 0.15wt%,the lubricant obtained the best lubricating performance.The friction coefficient and wear scar diameter reduced by 70.6% and 41.3%,respectively,compared with 5CB.The effect of temperature on the lubricity of graphene/5CB was studied.It was found that the outstanding lubricity of the lubricant depends on the good dispersion effect of graphene and the lubricity of 5CB in liquid crystal state.It is found by analyzing its lubrication mechanism that graphene reduces the friction coefficient and improves the wear resistance by forming a protective layer with low shear resistance and high wear resistance on the friction surface during the friction test.The lubricating properties of h-BN/5CB with micron h-BN(h-BNμ)and nano h-BN(h-BNn)as additives were studied on a ball-on-plate tribotester under different test loads and different additive concentrations.It is found that h-BNn has more obvious antifriction and antiwear effects than h-BNμ.The h-BNn/5CB has the best lubricating performance when the h-BNn concentration is 0.01wt%.The h-BNn/5CB has the lowest friction coefficient and the highest wear resistance under test load of 2N.Compared with 5CB,the friction coefficient and the wear scar diameter were reduced by 14.3% and 33.8% respectively.The mechanism of anti-friction and anti-wear of h-BNn was studied.It was found that h-BNn entered the friction interface during the friction test,filling the scratches on the friction surface and preventing the scratches from deepening further.The h-BNn that continuously enter the friction interface forms a continuous physical protective layer on the friction surface to protect the friction surface and reduce the friction resistance,thus reducing the friction coefficient and wear.