Temperature Sensitive Lubrication Behavior Of PNIPAM Microgels

About one third of the energy in modern mechanical equipment is lost due to friction between moving mechanisms,and it will also bring wear,resulting in damage and failure of mechanical structures.The best way to reduce friction and wear between moving parts is to improve lubrication between relative moving surfaces.Water has good cooling ability,low price,wide source and renewable characteristics,which makes water-based lubrication widely used in rolling,grinding and cutting,artificial joint lubrication and other fields.However,the low viscosity of water and poor film forming limit its lubrication.Therefore,it is of great practical significance to improve the lubricity of water in these fields.In this dissertation,poly(N-isopropylacrylamide)(PNIPAM)was successfully prepared by emulsion polymerization.By adjusting the concentration of reactants,PNIPAM microgels with different diameters were prepared.The size distribution of PNIPAM microgels was concentrated,and spherical structure of the microgels was regular.The particle size of PNIPAM microgel decreased with increasing temperature,and the particle size decreased rapidly after exceeding the critical temperature at ~31 ?.The influence of microgel concentration,particle size and temperature on the lubricity of microgel aqueous solution were studied by using PNIPAM microgels as an aqueous additive.The results show that the PNIPAM microgels have obvious characteristics of temperature sensitive lubrication.It can play an elastic ball bearing lubrication effect at the frictional interface,and significantly improve the lubricity of the aqueous solution.The smaller the microgel is,the easier it is to enter the frictional interface.Moreover,the addition of microgels is conducive to the formation of protective oxide film on the friction surface,reducing the wear of the material.The temperature-sensitive lubrication mechanism is that the temperature rise causes the microgels to lose water and collapse,resulting in a decrease in the lubrication performance of the aqueous solution.Furthermore,the temperature continues to rise,and the microgels continues to lose water and shrink into compact spherical particles,improving the lubricating properties of the aqueous solution.PNIPAM microgels were added into the simulated synovial fluid,and the effects of friction conditions and temperature on the lubrication performance of the simulated synovial fluid were studied.The experimental results show that PNIPAM microgels can improve the lubricity of the simulated synovial fluid under low load conditions.Moreover,the microgels also exhibits significant temperature sensitive lubrication characteristics in the synovial fluid.This is because when the temperature rises,the microgels shrink and adsorb on the surface of synovial protein molecules to lubricate together and improve the lubrication performance.However,the temperature continues to rise,and the interaction between microgels and synovial protein molecules precipitates together from the solution,resulting in worse lubricating property.