Design And Preparation Of Ti₃C₂/Polymer Composites For Electromagnetic Interference Shielding

With the rapid development of electronic communication equipments,electromagnetic pollution will not only adversely affect the stability and working life of electronic equipment,but also threaten human health and increase the risk of human disease.Therefore,the elimination of harmful electromagnetic waves is very important for the protection of electronic communication equipment and the maintenance of human living environment.While traditional EMI shielding materials such as metals have excellent electrical conductivity,showing good EMI shielding ability,but the easy oxidation,easy corrosion,high density and high processing cost seriously limit their application.Electromagnetic-shielding polymer composites are generally composed of conductive fillers and insulating polymer materials.They have the characteristics of light weight,easy processing,low cost and good corrosion resistance,and are expected to become a new generation of electromagnetic interference shielding materials.Transition metal carbide/nitride（MXene）is a new type of two-dimensional（2D）nanoconductive filler with metal-like conductivity,large specific surface area,excellent mechanical properties,easy processing and abundant hydrophilic functional groups（-O,-OH,-F）.However,MXene（Ti₃C₂）sheets tend to form tight packing structures between each other,which hinders its practical application.Polymers are widely used as effective"bonding phases"to improve the mechanical strength and flexibility of MXene-based macrostructures.Therefore,in this thesis,Ti₃C₂/polymer composites were prepared by physically cross-linking method.The microstructure and electrical conductivity of these composites were systematically studied,and their applications in electromagnetic interference shielding and other fields were also studied.The research work of this thesis is as follows:1.Design and preparation of Ti₃C₂/PU sponge composite material and its application in electromagnetic interference shieldingThrough impregnation method,we have prepared the Ti₃C₂/PU porous multifunctional composite material with large area,light weight,flexibility,large-scale production,good shielding performance and fast photo-/electro-conversion efficiency.By changing the pore sizes and impregnation times of the sponge,the electromagnetic interference shielding,electrical conductivity,electrothermal and photothermal properties of the composite material can be regulated.The composite material P₆₀F₃T_47.52 has good electrical conductivity of 153.9 S m^-1.The high conductivity makes the porous composite material have good electromagnetic interference shielding performance.Its total electromagnetic interference shielding efficiency（SE_T）is 86.2 d B,electromagnetic interference shielding reflection efficiency（SE_R）is 5.9 d B,and electromagnetic interference shielding absorption efficiency（SE_A）is 80.3 d B.The increase of SE_A effectively reduces the secondary reflection of electromagnetic wave.The electromagnetic shielding anechoic chamber made of composite material P₆₀F₃T_47.52 has the advantages of excellent shielding performance,simple production process,low cost,light weight and portability,which can be applied in information protection,data security,electromagnetic radiation prevention and other scenarios.In addition,Ti₃C₂has high conductivity and good light absorption ability in a wide band,which makes the composite material P₆₀F₃T_47.52 have good electrical/photothermal conversion ability.Under the low driving voltage of 2 V,the composite material P₆₀F₃T_47.52 can reach about 59.8℃within 15 s,and maintain a stable temperature over 800 s.Under the irradiation of near infrared（NIR）light,the temperature can reach 119.4℃after 15 s,and under the irradiation of solar source,the saturation temperature can reach 70.8℃within 120 s,and has excellent cycle stability.The Ti₃C₂-based porous polymer composite integrates high EMI shielding performance,fast electric/photothermal conversion rate,simple preparation method and wide adaptability,and has broad application prospects in the next generation of flexible multifunctional electronic devices and aerospace fields.2.Design and preparation Ti₃C₂/VAE composite coating and its application in electromagnetic interference shieldingThrough physical cross-linking method,Ti₃C₂/VAE composite coatings with excellent shielding performance and wide application range were prepared.Ti₃C₂ nanosheets have strong hydrogen bond interaction with vinyl acetate copolymerization emulsion（VAE emulsion）.The composite coating can produce good adhesion strength to various substrates.The composite coating T₃₅V₂ not only has a certain viscosity（viscosity value is 12098.0 Pa·s）,but also can meet the electrical conductivity requirements(conductivity is 3494.3 S m^-1).The wires are connected to a small light bulb,which can be lit under 1.5V DC power supply.After 180 days in natural environment,the SE_T of the composite coating film can still reach 21.2 d B,while the SE_T of pure Ti₃C₂ film is reduced from 32.7 d B to 12.7d B,which proves that the composite coating has good stability.In addition,Ti₃C₂/VAE can be applied to a variety of substrates commonly used in the X-band（8.2-12.5 GHz）field,whether flat or uneven surface.This work provides a promising design idea for electromagnetic interference shielding composite coatings to eliminate the adverse effects of electromagnetic radiation caused by the miniaturized electronic devices and devices with irregular surfaces in the field of 5G communication.