Research On Structural Design And Electromagnetic Interference Shielding Performance Of Ti₃C₂T_x Composite Materials

The excess electromagnetic radiation generated by electronic equipment during operation not only damage the accuracy of apparatus,but also threaten human health.The one of the most effective methods to eliminate electromagnetic interference is making electromagnetic shielding materials to protect the objects.At present,the shielding mechanism of most electromagnetic shielding materials is mainly reflection mechanism.Due to the impedance mismatch,the reflectivity exceeds 90%that causes serious secondary pollution of electromagnetic wave.Therefore,making materials with low reflection and high electromagnetic shielding efficiency is a challenge in the field of electromagnetic shielding.According to structure classifications,electromagnetic shielding materials can be divided into bulks,foams,films,etc.Films are widely used because of their advantages such as thin thickness,easy molding,and flexibility in electromagnetic shielding applications.Owing to the limitation of impedance mismatch,it is a contradictory between reducing electromagnetic wave reflection and increasing electromagnetic shielding performance.Therefore,in the current research,high electromagnetic shielding materials often have high reflectivity because of their high conductivity,and low reflection electromagnetic shielding materials can not obtain high electromagnetic shielding performance.Due to excellent metallic conductivity,hydrophilicity,mechanical properties and high specific surface area,titanium carbide（MXene,Ti₃C₂T_x）,a new two-dimensional nanomaterial,has great potential in the field of electromagnetic shielding.In this paper,Ti₃C₂T_xis introduced into multilayer materials through structural design to construct functional low reflection composite films.Relevant research contents are as follows:1.MXene nanosheets were successfully prepared by in-situ formation HF etching.A series of electromagnetic shielding flexible multilayer films were obtained through layer by layer self-assembly of positive charges chitosan solution and negative charges MXene suspension by spin coating method.This chapter deeply investigates the electromagnetic shielding performance and thermal properties with different MXene content by vector network analyzer and thermal infrared analyzer.To our surprise,when the MXene content is 25.9%,the conductivity of the composite that base on the construction of MXene continuous conductive layer is 969 S m^-1,the plane thermal conductivity is 6.3 Wm^-1K^-1,and the average total electromagnetic shielding efficiency in X-band reaches 40.8 d B which has reached the standard of commercial electromagnetic shielding performance.In view of the interface impedance matching and the multiple reflection of multilayer interface,the electromagnetic shielding effectiveness of CS/MXene multilayer composite films are mainly based on electromagnetic absorption loss.This electromagnetic shielding material with excellent conductivity,thermal conductivity and flexibility is expected to be used in the next generation of wearable devices.2.Although CS has good impedance matching in the composite film,the absorption of CS polymer to electromagnetic wave is low.Therefore,in this chapter,magnetic materials are introduced into MXene to further reduce the reflectivity.We have successfully prepared high absorption and low reflection MXene-CNF-Co/C multilayer composite films by using the alternating vacuum filtration method.The electromagnetic shielding effectiveness of the composite films were regulated by adjusting the weight ratio of MXene to Co/C.The results demonstrate that the percentage of SE_Ain SE_Tis 99%,and the R reach 0.001（That means only 0.1%of electromagnetic waves are reflected）when the weight ratio of MXene to Co/C is 1:5and the thickness of MXene-CNF-Co/C-5 is about 1.5 mm.The MXene-CNF-Co/C composite film demonstrates the absorption-dominant EMI shielding mechanism which can reduce the secondary electromagnetic radiation pollution.The structural design of MXene-CNF-Co/C composite film maintains excellent MXene conductive network,and Co/C can effectively absorb electromagnetic waves.The method provides a new idea for the design of electromagnetic shielding materials with high absorption and low reflection.3.According to the previous research,it is found that the introduction of multilayer structure and Co/C can effectively reduce the reflection of electromagnetic wave.In order to effectively control the multilayer structure and composition,we select a mixture of Co/C magnetic particles and environmentally friendly waterborne polyurethane（WPU）as the electromagnetic wave absorption layer and MXene as the conductive layer in this chapter.The thin composite films were prepared by using alternating blade coating.The multilayered structure emerges an absorption-reflection-reabsorption process,which makes electromagnetic shielding materials obtain high electromagnetic shielding effectiveness and low reflectivity.MXene-WPU-Co/C-10 composite film with a thickness of 0.2 mm can obtain 31 d B in X-band with low MXene content（MXene content is 10%）,and the R reach 0.01.Compared with the research of similar electromagnetic shielding materials,the strategy that is low-cost,thickness controllable and structure controllable provides a new idea for the research of efficient and low reflection electromagnetic shielding films.