Effects Of Coupling Agent On The Water-Based Lubrication Characteristics Of Konjac Glucomannan

Traditional oil lubrication has the disadvantages of environment pollution and solidification at the micro-nano scale.In addition,petroleum resources are not renewable,and the development of new green environmentally friendly lubricants is imperative.Water-based lubrication is a new type of lubrication method.By adding various additives in water,the hydration effect is used to achieve ultra-low friction at the interface of the friction pair.Water-based has huge application potential in precision mechanical transmission.In this paper,we used Konjac Glucomannan(KGM)as water-based lubrication additive,three kinds of silanes as coupling agents,and quartz glass as friction pair.The micro friction and wear test and molecular dynamics simulation were combined to investigate the interaction between KGM and different coupling agents.The mechanism of water-based lubrication was explored under surface contact conditions.The main research contents are as follows.1.Using quartz glass as the friction pair,the interaction between three coupling agents and KGM was studied.The water-based lubrication mechanism of the KGM-coupling agent mixed solution was emphatically analyzed.The results indicate that 3-Mercaptopropyl trimethoxysilane(MPTS)and KGM have the synergy effect to reduce friction.The friction coefficient with 0.3 wt.%KGM and 5 wt.%MPTS mixed solution reduced by 34.2%relative to 0.3 wt.%KGM solution.The hydration layer and stern layer work together to achieve superlubrication.The Si-O bond in MPTS forms a new covalent bond with the hydroxyl group in KGM,which changes the water-based lubrication characteristics of the KGM solution.The mixed solution is more likely to spread on the surface of the friction pair because MPTS reduces the surface tension of the mixed solution.With the increasing concentration of MPTS,the viscosity of the mixed solution gradually increases.2.Equilibrium molecular dynamics simulations were used to study the synergy effects between three coupling agents.and KGM.The effects of temperature and pressure on the adsorption behavior of KGM-MPTS mixed solutions on the SiO2 surface are explored.Interfacial binding energy and related RDF analysis show that the synergy effect between MPTS and KGM is the best.As the temperature increases,the binding energy at the interface decreases continuously;When the temperature increases,the Vander Waals force between the molecules decreases,the maximum relative concentration of the water molecules in the Z direction decreases,and the gap of radius of gyration between the KGM molecular chain keeps shrinking.The distance between the centroids of two systems keeps decreasing.When the pressure increases,the interface binding energy and interfacial adsorption force decrease first and then increases,resulting in first decreasing and then increasing of the maximum relative concentration of water molecules in the Z direction and the gap of radius of gyration of KGM molecule,and first increasing and then decreasing of the centroid distance between the two systems.3.The effects of shear rates on the shear rheology behavior of KGM-MPTS mixed solution on the surface of SiO2 confined region were investigated by nonequilibrium molecular dynamics simulation.As the shear rate increases,the relative concentration of the fluid layer shows no significant difference.At each shear rate,significant velocity stick-slip phenomenon appears in the fluid layer,and the fluid molecular chains and atoms on the surface of the rigid wall are constantly adsorbed and detached,which results in changing of the rate of fluid molecules.With the shear rate increasing,the temperature of the fluid layer increases due to the increased molecular thermal motion.At the same time,the mean square displacement of the fluid layer increases,and the fluid layer becomes easier to migrate.The decreasing in viscosity of the fluid means shear thinning phenomenon.The shear rate is set from 0.1 A/ps to 0.9 A/ps,the average number of hydrogen bonds of the fluid layer is reduced by 57.6%.The decreasing of the hydrogen bond number in the fluid reduces the viscosity of the liquid.