Preparation And Electromagnetic Interference Shielding Properties Of Multi-Layered Polymer Nanocomposites

With the wide application of electromagnetic technology,electromagnetic waves are flooded in various environments,seriously endangering biological life safety,leaking confidential information technology and interfering with the normal operation of electronic devices.The electromagnetic shielding material can effectively block the propagation of electromagnetic waves and protect the shielded object.At present,polymer-based electromagnetic shielding materials have been widely studied due to their lightness,thinness,ease of processing,and excellent mechanical properties.Among them,the conductive polymer-based composite shielding material has high shielding performance,but the reflection loss is very high.In order to prepare a shielding material that mainly absorbs loss,it is necessary to enhance the ability of the shielding material to absorb electromagnetic waves by increasing the dielectric and magnetic losses as much as possible.The combination of conductive materials and magnetic materials can effectively improve impedance matching and enhance the absorption and dissipation of electromagnetic wave energy by shielding materials.However,no in-depth research has been carried out on how to make full use of these two materials to obtain high electromagnetic shielding performance and low reflection loss.Therefore,it is a meaningful research work to explore the influence of different magnetic/conductive composite systems on the electromagnetic shielding performance through structural design.In this thesis,high-dielectric MXene was used as conductive filler,high-permeability PDA@CIP and ultra-high aspect ratio Fe₃O₄ nanosheets were used as magnetic filler,and water-based polyurethane WPU was used as matrix.Magnetic/MXene was prepared by vacuum filtration and hot pressing process.Polymer electromagnetic shielding composite materials,and the shielding properties of different composite films were investigated.Four kinds of flexible composite films with different dispersion structures were prepared by low-dielectric polydopamine（PDA）modification of CIP,mechanical blending and hot pressing.The polydopamine-modified carbonyl iron has improved dispersibility,enhanced electromagnetic shielding performance and weakened reflection loss.The EMI performance of the double-layer hot-pressed structure film is more than two to four times that of the ordinary blended composite film.Among them,the PDA@CIP/MXene/WPU hot-pressed composite film has a high electromagnetic shielding performance of 40.3 d B and an average reflection loss SE_R of only 2.8 d B when the content of MXene is0.76 wt%.In addition,four dispersive structure models were studied by CST simulation,and it was found that the hot-pressed double-layer structure had higher energy loss than the blended structure,and a lower surface electric field could be obtained by combining the dispersed CIP and incident through the magnetic layer.Through the self-assembly and hydrothermal reaction of the surfactant PVP,large-scale and ultra-thin（more than 50μm in length,3-6nm in thickness）ferromagnetic iron tetroxide nanosheets were prepared for the first time.Single-layer and double-layer blended Fe₃O₄/MXene/WPU composite films were prepared by vacuum filtration.The composite of Fe₃O₄ nanosheets with MXene can greatly improve the shielding performance of the composite film and reduce the reflection loss.At the same proportion,the shielding performance of the Fe₃O₄/MXene/WPU double-layer composite film is 3 times that of the MXene/WPU composite film and 1.5 times that of the single-layer composite film.Experiments and theory show that the multi-layer structure design of conductive and magnetic layers strongly enhances electromagnetic losses and absorption.In addition,the mechanical strength of the composite films was significantly improved after the introduction of magnetic and conductive fillers.