Studies On Preparation And Properties Of Functionalized Mxene And Their Conductive Inks

In order to solve the electromagnetic interference（EMI）and electromagnetic compatibility problems in electronic equipment caused by communication,it is urgent to develop efficient,thin,and form-fitting EMI shielding materials.The EMI shielding materials used for military equipment protection also face the challenges of large-area processing,lightweight and anti-infrared detection.Therefore,it is of great scientific significance and application value to develop EMI shielding materials that are easy to process,large-scale,form-fitting,and infrared camouflage.The development of highly conductive ink is the key to realizing easy processing,batch manufacturing and designability of EMI shielding materials.Two-dimensional（2D）transition metal carbide/nitride（MXenes）have the characteristics of high conductivity,good liquid phase processing and low infrared emissivity,showing great application potential in the field of EMI shielding.However,Ti₃C₂T_XMXene is easy to oxidize and its ink rheological properties are difficult to improve,which seriously limit the storage and coating/printing processing of MXene ink.Moreover,the performance regulation and infrared camouflage function of MXene EMI shielding material also need to be further studied.This dissertation explores a variety of functional modification methods of MXene nanosheets,and prepares MXene-based inks with excellent rheological properties and high chemical stability,and realizes large-area and accurate coating/printing processing of MXene inks.MXene-based compact coating with high conductivity and low infrared emissivity,MXene-based patterning coating for EMI shielding switch and adjustable infrared radiation,and MXene-based flexible coating with highly efficient EMI shielding and dynamic infrared camouflage performance are obtained.The main research contents and results are as follows:（1）Catecholamine micro-crosslinked MXene inks and their highly efficient EMI shielding and infrared stealth applications:In order to solve the problems of high conductivity,low infrared emissivity,and excellent rheological properties in MXene-based inks for the preparation of efficient EMI shielding and anti-infrared detection coating,micro-crosslinked MXene-based inks with excellent rheological properties are prepared based on the electrostatic and hydrogen bond interaction between catecholamine and MXene.The MXene-based compact coating with high conductivity and low infrared emissivity is constructed by shear-induced orientation and inter-sheet micro-crosslinking strategies.At a low modifier dosage（0.5 wt%）,the viscosity of MXene/catecholamine ink is significantly increased（≈257 times）.The synergic shear-induced orientation and micro-crosslinking of catecholamine densify the MXene/catecholamine coating structure,resulting in high conductivity,excellent EMI shielding properties,and low infrared emissivity of coating.After heat treatment,the compact MXene/catecholamine coating with reduced lamellar spacing has high conductivity(1.2×10⁴S cm^-1),high specific EMI shielding effectiveness(2.0×10⁵d B cm²g^-1)and excellent durability.In addition,due to the efficient rheological regulation of catecholamine,a small amount of catecholamine does not change the low infrared emissivity characteristic of MXene-based coating,and endowing ink coating and brushing capabilities,thus achieving the preparation of infrared stealth/camouflage coating with large area and patterning.（2）Controllable PDA surface-grafted MXene inks and their applications in EMI shielding and infrared radiation regulation:In order to solve the problems of MXene ink’s easy oxidation,poor rheological properties and difficult to adjust infrared emissivity in the development of printed MXene-based materials with EMI shielding and infrared radiation regulation,the controllable grafting of prepolymerized polydopamine（PDA）on MXene surface is carried out.MXene nanosheets coated with PDA nanoshells（p-MXene）are obtained,and the antioxidant and rheological properties of the ink are improved.PDA shell effectively protects MXene from water and oxygen erosion.p-MXene’s rich surface chemistry improves the interaction between nanosheets and rheological properties of ink.Compared with pure MXene ink,p-MXene ink can be stably stored at room temperature for 30 days without being significantly oxidized.The high viscosity,excellent viscoelasticity and thixotropy of p-MXene inks allow for high precision,patterned screen printing and a wide range of liquid phase processing on a variety of substrates.The EMI shielding switch and electromagnetic wave quantitative transmission are realized by deflecting screen printing MXene-based EMI shielding micro-gratings,and the regulation mechanism is clarified,which provides a new way for the regulation of electromagnetic wave.At the same time,the infrared emissivity of p-MXene can be adjusted by changing the modification amount of PDA nanolayer.p-MXene composite coatings with different infrared radiation abilities have been prepared by printing,which have broad prospects in infrared anti-counterfeiting patterns and infrared camouflage.（3）Ion crosslinked MXene/sericin inks and their EMI shielding enhancement and infrared camouflage applications:Aiming at the problem that EMI shielding material is difficult to take into account the lightweight,low cost and high performance,a method is established to construct the macroscopic 3D ripple shape of thin and flexible MXene-based coating with corrugated template to enhance the EMI shielding performance of the coating.The viscosity and moduli ratio of MXene-based ink are improved by crosslinking sericin-modified MXene nanosheets with calcium ions,and the flexible conductive coating is prepared by blade coating on the polymer film substrate.The 3D ripple shape of the flexible coating significantly enhances its EMI shielding effectiveness.The increase in the number and depth of ripples can improve the shielding effectiveness and reduce the reflection shielding effectiveness ratio.Based on the analysis of the shielding mechanism and the finite element simulation of electric field distribution,the EMI shielding gain mechanism of 3D"rippling"of the coating is elucidated.Compared with 2D flat coating,the shielding effectiveness of coating with 3D ripple after the normalization of cross-sectional area is greatly improved（213%）,indicating the advantages of 3D"rippling"strategy in lightweight,low cost,high performance and other aspects.In addition,combined with the low infrared emissivity and good Joule heating performance of the MXene-based conductive coating,the dynamic control of the infrared detection temperature of the coating surface is realized,which gives the coating dynamic infrared camouflage properties.It is expected to be applied to the masked infrared camouflage and EMI shielding coating of equipment.