Study On Charge Characteristics Of Nano-dielectric By Atomic Force Microscopy

It is generally believed that the interface area formed between nanoparticles and polymer matrix plays a major role in the dielectric,conductance,and space charge characteristics of nano-dielectrics.The study of charge generation,injection and movement in nano-dielectric is of great significance to understand the mechanism of nano-dielectric properties.In order to study the important role of the interface area in the evolution and motion of charge on the micro scale,various modes of Atomic Force Microscopy?AFM?were used,including contact mode,Kelvin Probe Force Microscopy?KPFM?,Electrostatic Force Microscopy?EFM?,etc.The surface morphology of LDPE,Si O₂/LDPE and Mg O/LDPE and their charge motion characteristics were studied.COMSOL Multiphysics simulation was used to simulate the electric field distribution of the probe under different modes,and the phase information of the EFM was analyzed.By using the contact mode of AFM,charge was injected on the surface of the sample.KPFM was then used to measure the change of potential with time after charge injection,and the data were fitted.The results showed that the surface potential of Si O₂/LDPE nanocomposites disappeared more slowly than that of pure LDPE,while the surface potential of LDPE doped with hydrophobic Si O₂ was even slower.The distribution,movement and dissipation of charge generated naturally on different dielectric surfaces and injected by probe were observed and studied by EFM.It was found that both the naturally accumulated charge and the injected charge in Si O₂/LDPE and Mg O/LDPE nanocomposites were easy to accumulate in the interface area,and the charge was more difficult to dissipate than that in pure LDPE.It indicates that the charge is trapped in the interface area and cannot be released.These accumulated charges form a barrier and prevent the further injection of charge,thus improving the dielectric performance.In addition,the Pulse Electro-Acoustic?PEA?short-circuit test was conducted after the sample was polarized and the change of total charge was calculated.The trend of charge decay in the KPFM and EFM test is also generally consistent with that in PEA short-circuit test and can be used to verify one another.This result establishes the connection between the microscopic charge distribution and the macroscopic dielectric characteristics,reveals the law of the charge movement,and verifies that the important role of the interface region in the nano-dielectric:it can inhibit the space charge injection in the nano-dielectric at microscale.It provides a strong evidence for the interface and related theoretical research,and develops a new characterization method.