Mechanical And Frictional Investigation Of Barium Titanate And PVDF Based On Atomic Force Microscopy

When machinery entered the microscopic field,surface forces like adhesion force and friction force have become the key factors for device lifespan and performance.At the micro-nano scale,research shows that frictional energy consumption mainly includes phononic dissipation and electronic dissipation.At present,the influence of electronic dissipation is not clear.Barium titanate and PVDF are piezoelectric materials,so they can generate polarized charge on the surface under pressure,which make them become ideal materials for studying electronic friction.Atomic Force Microscopy(AFM)has been widely used in the measurement of electrical and mechanical properties of materials at micro-nano scales due to its ultra-high spatial resolution and measureing sensitivity.Therefore,in this thesis,the mechanical properties and frictional properties of barium titanate and PVDF were studied using AFM,after which the effect of surface charge density on friction was discussed.The mechanical properties of the material will affect the friction to some extent.Therefore,based on the Oliver-Pharr and Hertz models,the elastic modulusi of barium titanate and PVDF were measured by atomic force microscopy and the values were about 290 GPa and 500 MPa,respectively.What's more,the effects of adhesion,scanning speed of the AFM probe,pressure exerted by the tip on the friction were studied.The experimental results show that friction increases with the increase of the adhesion between the probe and the material.As the scanning speed increases,friction increases slightly.For barium titanate,friction increase linearly with the positive pressure,which obeys the traditional Amontons law.For PVDF,the linear relationship between friction and positive pressure is valid under relatively small load.As the normal load increases,friction has a tendency to increase nonlinearly.The reason for this phenomenon are the increase of surface roughness and surface charge density caused by the deformation of the piezoelectric material.Then,the effect of surface charge density on friction is further studied by applying voltage.The experimental results show that the increase of the surface roughness has little effect on the friction.While the rise of surface charge density contributes greatly to the increase of friction force.In summary,the atomic force microscopy is used to accurately measure and evaluate the mechanical and frictional properties of piezoelectric materials.At the same time,it is found piezoelectric materials has a certain degree of dependence on surface charge density and it is expected that friction can be actively regulation achieved by this method.