Research On Film Forming Characteristics And Lubrication Mechnism Of Biomimetic Lubricating Materials Under Water Lubrication Environment

There are highly efficient water lubrication systems in nature such as natural joints,eyelids and teeth,which maintain an ultra-low coefficient of friction and a service life of up to 70 years even under harsh conditions.Inspired by this,scientists have prepared a variety of bionic lubricating materials based on bionic principles in order to obtain good lubricating properties,such as macromolecular polymer brushes and hydrogels,and have carried out a series of studies on their biomechanical and frictional wear properties.However,to date there is still no consensus on the lubrication enhancing behaviour and water lubrication mechanism these bionic lubricating materials exhibit.Based on this,this research work focused on investigating the film formation property and the lubrication mechanism of bionic lubricating materials lubricated by water using a ball-disk point contact film thickness measurement apparatus,The main studies are shown below:(1)Two polymer brushes PSPMA with low and high degree of hydration were prepared on the surface of ceramic spheres and glass discs,respectively,using 2 different initiators.Optical measurement results from transient loading tests under static conditions indicate a high load carrying capacity for highly hydrated polymer brushes;The curve of film thickness with speed shows a large difference in the values of film thickness between the two,for example,the film thickness of the polymer brush with low hydration is about35 nm at a speed below 16 mm/s,while the polymer brush with high hydration is up to100 nm or more,this confirms that the hydration effect of polymer brushes is the key to obtaining excellent lubrication properties.(2)To improve the wear resistance of the polymer brushes,an inorganic hybrid persistent initiator coating(PIC)was first prepared on the surface of the glass discs,on which the polymer brushes PSPMA were subsequently grafted by initiating polymerization reaction.A comparison of film thickness and friction measurements under pure water and monomer solution lubrication conditions showed that film thickness decreased and friction increased over time under water lubrication conditions especially under harsh test conditions,due to the gradual destruction of the grafted polymer brush PSPMA during the friction process.While under the test conditions of monomer solution lubrication,slip-to-roll ratio SRR of 0.05 and speed less than 16mm/s,the film thickness value basically remained above 125 nm and the coefficient of friction remained below0.05 for 600 s.It is assumed that while the PSPMA is destroyed during the frictional movement,the initiator embedded in the PIC coating can rapidly re-form new PSPMA on the friction surface by initiating a polymerisation reaction in the monomer solution.(3)A cross-linked structured hydrogel(Gel MA)coating with a thickness of approximately 125 μm was prepared on the surface of the friction substrate by copolymerisation with a small molecular weight polyethylene glycol diacrylate(PEGDA)using a light-curing method.Three types of hydrogels with different degrees of hydration were obtained by controlling the length and duration of their water loss.The results of loading and unloading tests show that the biomechanical properties of hydrogels with a high degree of hydration are good.Furthermore,the optical interference images at different speeds demonstrate that the lubrication behaviour of the hydrogel surface is different and very sensitive to the sliding speed and time.It is hypothesized that the complex lubrication behaviour presented is influenced by a combination of the hydrodynamic effect induced by triobological movement and the hydration effect of the hydrogel.In this study,bionic lubricating materials with high degree of hydration,high wear resistance and cross-linked chemical structure were obtained by improving the preparation method.The results demonstrate that they can obtain better lubrication property,which would provide new ideas for the design of bionic lubricating materials with excellent water lubrication performance and further reveals the water lubrication mechanism.