Study On Structure Design And Performance Tunability Of Two-Dimensional Transition Metal Carbide-Based Electromagnetic Interference Shielding Materials

With the rapid development of wireless communication technology and electronic devices,developing lightweight electromagnetic interference（EMI）shielding materials with high-performance and multi-functional is imperative to solve the growing problem of EMI issues.The rise of intelligent devices and active protection systems has led to the transition of EMI shielding materials from traditional passive protection to novel active protection,to achieve controllable shielding of electromagnetic（EM）waves.However,the controllable structure construction of EMI shielding materials for lightweight,conformalization and high-performance is challenging.Meanwhile,EMI materials with dynamically tunable performance are still in their infancy,and the problems of the large thickness,the limited control range,poor reversibility,and the unclear mechanism need to be solved urgently.In this dissertation,two-dimensional（2D）transition metal carbide（MXene）-based EMI shielding materials are used as research objects.The performance tunability of EMI shielding materials is achieved through structure design.Lightweight EMI shielding materials with high electrical conductivity and excellent thermal insulation properties,dynamically tunable EMI shielding materials driven by stress,and stimuli-responsive EMI shielding materials are fabricated.A new method for performance tunability through structure design is proposed.The relationship between the hierarchical structure of the material and the EMI shielding performance is elucidated.The main research contents and results of this dissertation are as follows:（1）Study on structure design and performance of lightweight and porous MXene-based EMI shielding materials:This chapter aims to solve the conflict between lightweight and high-performance of EMI shielding materials.A new method of emulsion-based inks through the controllable interfacial assembly of MXene is proposed for the 3D printing of lightweight EMI shielding materials and the controllable construction of the hierarchical structure.Emulsion-based inks are prepared using positively charged ligands（octadecyl amine）to modulate the interfacial properties of MXene to enable its assembly at the water-oil interface.Interactions between ligands anchored on the surface of different emulsion droplets determine the rheological properties of inks,with an increase in viscosity and moduli of 3 orders of magnitude compared to the same concentration dispersions.The 3D printing of ultralow-concentration 2D nanomaterials inks(MXene:5 mg m L^-1,graphene oxide GO:3.6 mg m L^-1)is achieved.By adjusting the emulsification parameters,the internal volume fraction of the emulsion,and the MXene concentration,not only the rheological properties of the emulsion ink are optimized,but also the microstructure of the emulsion ink is regulated.Moreover,a 3D printing method for ultralight EMI shielding materials is established to achieve the controllable construction of the hierarchical structure and EM waves attenuation network of materials.The printed MXene foams with ultralow density(4.1 mg cm^-3)integrate high electrical conductivity(～403 S m^-1),high EMI shielding performance（64 d B）,and excellent thermal insulation property(25 m W m^-1K^-1).Furthermore,the relationship between the microporous structure and the EMI shielding performance of the material is investigated.The increase in cell size facilitates the construction of the conductive network,which improves the electrical conductivity and EMI shielding performance of MXene foam.（2）Study on structure design and performance of dynamically tunable MXene-based EMI shielding materials:To dynamically tune the EMI shielding performance of materials,the reversible transition from shielding states to transmitting states is dynamically regulated through structure changes controlled by stretching.Metal ions(Al³⁺)are introduced to develop the Al³⁺-MXene ink with high electrical conductivity and excellent rheological properties by moderately cross-linking MXene nanosheets.Flexible electronic devices and EMI shielding materials with customized structures are prepared by extrusion printing.Combining experimental results with theoretical simulations,the high-performance flexible MXene mesh is constructed by exploring the influence of the size and shape of the mesh pores on the EMI shielding performance.Furthermore,a stretchable EMI shielding structure material is prepared by taking advantage of the multi-material integration of printing.EMI shielding efficiency（SE）of the material can be dynamically and reversibly tuned between 8.2-34 d B,enabling switching between shielding states and transmitting states,with no significant degradation of performance and its tunable range after 500 cycles.（3）Study on structure design and performance of stimuli-responsive MXene-based EMI shielding materials:To achieve stimulus-responsive tunability of EMI shielding performance,a flexible film with both multi-stimuli response capacity and EMI shielding performance is prepared through the layer structure design.The bilayer GO/MXene film is prepared by the two-step vacuum-assisted filtration.The film possesses multi-stimuli response capacity for humidity,near-infrared light,and electricity due to the bilayer structure design and differences in affinity for water molecules of constructing base-element materials.In-situ monitoring of the amount and rate of water molecules desorbed from films during near-infrared light irradiation to investigate the actuation mechanism of films.A stimuli-responsive EMI shielding system based on EMI shielding performance and stimuli-responsive capacity of the bilayer film.The bilayer GO/MXene film can change shape according to external stimulations to achieve the switch between shielding states and transmitting states and the controllable shielding of EM waves.Moreover,the smart switch and the soft walking robot are manufactured based on GO/MXene film.