Study On Microscopic Charge Characteristics Of Special Structure Composite Polyethylene Based On Atomic Force Microscope

The interface region between the dopant and the matrix in the nanodielectric plays an important role in the performance of the material.The study of the charge evolution near the interface of the composite material is of great significance for revealing the dielectric mechanism of the nanodielectric.The shape of the doped particle and the charge evolution in the interface region exist connect.Atomic Force Microscopy（AFM）is currently the only means that can be used to detect the evolution of micro region charges.In the electrical mode of AFM,Kelvin Probe Force Microscopy（KPFM）and Electrostatic Force Microscopy（EFM）are the main methods to explore the interface mechanism.In order to explore the effect of particle shape and structure on the charge performance of the sample,this paper improves the sample preparation method and observation method to obtain conditions suitable for AFM observation.Using KPFM and EFM systems to study the evolution of surface charge of pure low density polyethylene（LDPE）,spherical and rod shaped silicon dioxide（Si O₂）doped LDPE,spherical and sheet shaped magnesium oxide（Mg O）doped LDPE,and the influence of particle shape on the interface charge distribution was verified,and the macroscopic and linkages for microscopic charge evolution.Charge injection was performed on the sample through the contact mode of AFM,and then the evolution law of the injected charge was observed by KPFM.The study found that the decay rate of the surface potential of the doped composite material was slower than that of pure LDPE.In particular,it was found that the potential attenuation was basically not attenuated when injected next to the particles in the rod shaped Si O₂/LDPE,and it was significantly attenuated after being injected away from the particles.The injected charge migrates towards the interfacial region near the particle.The results show that the particle doping introduces the interface region,which reduces the carrier mobility,and the interface trap effect between the special structure particles and the matrix is obviously easier to trap charges.The movement characteristics of the original charge and the injected charge of the sample were observed by EFM.It was found that the interface region of spherical and rod shaped Si O₂/LDPE traps easily bound charges,and it is difficult to dissipate the charges compared with pure LDPE.After injecting next to the rod shaped particles,the charge will be distributed along the particle contour.After injecting away from the rod shaped particles,there will be obvious charge accumulation at the end of the rod-shaped particles,indicating that there are more traps at the end of the rod shaped particles,which will bind more charges.The trap effect is obvious.In addition,the space charge distribution of the sample was measured by the pulse electroacoustic method（PEA）,and it was found that the doping of Si O₂ particles improved the ability of the material to suppress charge injection,and only a small amount of charge injection was injected during the polarization of the rod shaped particle sample.Comparing the PEA depolarization decay curve with the KPFM potential decay curve,it was found that both decreased exponentially with time,and the residual charge of the doped sample was higher than that of the pure LDPE sample,which verified the correlation between macroscopic and microscopic charge evolution.Through the above research,the observation and processing method suitable for AFM was obtained,the relationship between charge evolution and particle shape was revealed,the connection between microscopic charge distribution and space charge characteristics was established,and the important role of the interface region in composite materials was verified.It provides strong evidence for the study of interface theory.