Design And Preparation Of Lightweight And Flexible Electromagnetic Shielding Materials With Sandwich Structure

With the rapid development of the information era,a variety of intelligent electronic devices have emerged,which greatly facilitate the life of modern people.However,the electromagnetic pollution obtained has become a problem that should be concerned.Electromagnetic interference（EMI）can cause information confusion between devices,causing unnecessary economic losses,and in serious cases even affect the security and stability of the country.EMI shielding is one of the effective means to suppress electromagnetic pollution,so the research and development of high-performance EMI shielding materials is of great practical significance.Metallic materials possess ultra-high electrical conductivity,and thus play an important role in the field of EMI shielding,but in the current trend of lightweight EMI shielding materials,traditional metallic materials due to their high density,high hardness,and difficult to adapt to a variety of irregular surfaces,the application is greatly limited;and filled EMI shielding materials are widely studied because of its advantages in simple preparation,adjustable performance,but it is difficult to balance between their EMI shielding performance and mechanical properties,and the shielding mechanism and function are single.To solve the above problems,a metallic copper foil（Cuf）with microporous surface is selected in this thesis,and Cuf is covered with liquid silicone rubber（SiR）with low viscosity to interpenetrate into the microporous,and the two are combined into a lightweight EMI shielding material with sandwich structure by combining the advantages of high shielding and low surface density of Cuf and light mass of SiR.In addition,a lightweight flexible multilayer composite material with various shielding mechanisms and excellent shielding performance（SE）is also prepared by multi-layer structural design using electric and magnetic fillers and SiR composite.The principal studies are as follows:（1）Preparation and performance study of Cuf/SiR EMI shielding composites:A composites for EMI shielding tents and shielding rooms was prepared through the selection of the base material and the design of the structure,which solved the problems of high density and short service life of the above materials.Firstly,the influence of SiR viscosity on the structural molding of the composite was explored,and secondly,the introduction of nano-rough structure and reactive groups on the surface of Cuf greatly improved the interface adhesion between the two,and the influence of the surface structure of Cuf on the interface strength of the composite was discussed in detail,and the final Cuf/SiR composite exhibits ultra-high EMI SE,good flexibility,strong interface adhesion and low density.The average EMI SE of Cuf/SiR composite material in the range of 1.13-18 GHz is 111.5 d B,the specific electromagnetic shielding effectiveness is 85.75 d B·cm^-3·g,and the interfacial adhesive strength is 5.2 N·cm^-1.It also possesses excellent bending resistance and splicing performance,which exhibits considerable application prospects in the field of EMI shielding tents and shielding rooms.Finally,by adding carbon nanotubes to the SiR layer,it possesses the ability to absorb waves with the lowest RL value of 32.1 d B,which effectively weakens the electromagnetic waves reflected by Cuf and reduces the secondary radiation.Moreover,the preparation method of this composite is simple and accessible,which provides a method guide for the design and preparation of metal/polymer composites in molding.（2）Preparation and performance study of multi-layer multi-functional EMI shielding composites:Through the screening of fillers and the design of structure,an EMI shielding composite with various shielding mechanisms and functions was prepared,which solved the drawbacks of high filling content and single shielding mechanism and function of current filled EMI shielding materials.Firstly,the effects of filler content and dispersion on the conductivity and EMI shielding performance of single layer composites were investigated,and the relationship between their electrical and magnetic properties and shielding mechanism was analyzed.Then the composites with three-layer structure was prepared by co-vulcanization,enabling it to possess the ability to shield electromagnetic waves at low filler content（～10 wt%）.The effects of the structural arrangement and thickness of the three-layer composites on its EMI shielding performance were discussed in detail and fully explained in terms of the shielding mechanism.Finally,the electrical heating and sensing functions of the three-layer composite are expanded,the structural arrangement of ECB-Fe₃O₄-CNTs has the best EMI shielding effect,and the EMI SE reaches 23 d B when the thickness is 2.4 mm,which exceeds the standard value for commercial use.It has good flexibility and mechanical properties;it can be also heated to61.2°C with 2 min at 6 V DC voltage and can monitor the joint motion of human body in real time,which proves its great potential application in the field of flexible electronics.