Structural and Functional Design of Two-dimensional MXene Composites for Advanced Electromagnetic Applications

Abstract

As the high-frequency and high-density integration of modern electronic and communication systems accelerates, EMI has emerged as a critical bottleneck threatening signal integrity and system reliability. Traditional metal-based shielding materials have been widely adopted owing to their superior electrical conductivity; however, they suffer from intrinsic limitations such as high density, susceptibility to corrosion, difficulty in integration with flexible substrates, and performance degradation at reduced thickness. 2D Ti3C2Tx MXenes, possessing high surface area, tunable surface terminations, and metallic-grade conductivity, have garnered significant attention as next-generation EMI shielding materials. MXenes can deliver exceptional shielding effectiveness even in ultra-thin and mechanically compliant configurations due to their excellent charge transport and strong interfacial interaction, making them highly promising candidates for emerging platforms including wearable electronics, lightweight defense systems, and electric mobility and aerospace technologies. However, despite their metallic electronic structure, MXenes still face several critical challenges that must be addressed for reliable and scalable EMI shielding applications. First, MXenes are susceptible to oxidation and moisture-induced degradation, which progressively deteriorate their electrical conductivity and long-term shielding stability, particularly under humid or harsh environmental exposure. In addition, their intrinsically high electrical conductivity induces a reflection-dominated shielding. While beneficial for blocking incident waves, such excessive reflection can induce undesirable secondary EMI within densely integrated or high-frequency electronic systems. Furthermore, MXenes possess an anisotropic layered morphology that restricts heat transfer primarily within the in-plane direction. During electromagnetic attenuation, localized Joule heating, magnetic losses and dielectric losses can accumulate within the film, yet the limited out of plane thermal pathways hinder efficient multidirectional heat dissipation. These coupled challenges—environmental instability, secondary EMI generation, and anisotropic thermal management—necessitate advanced engineering strategies including surface and termination stabilization, impedance-matched absorber architectures, heterostructures with magnetic or dielectric fillers, and the introduction of vertically aligned or thermally conductive pathways to ensure stable, absorption-dominant shielding performance and efficient heat spreading. In this thesis investigates the structural and functional design of MXene-based electromagnetic materials that overcome the inherent limitations of 2D layered conductors through chemical synthesis control and interfacial engineering. A high-quality Ti3C2Tx MXene synthesis strategy was established by precisely regulating acid concentration, etching kinetics. This controlled synthesis minimizes defect formation, suppresses unwanted oxidation, and enhances flake integrity and electrical performance. By chemically grafting protective functional groups and optimizing terminal compositions, the resulting MXene exhibits substantially improved environmental durability and long-term electrical stability, enabling reliable performance in harsh or humid operational environments. To advance MXene toward next generation electromagnetic applications, further integrates absorption-dominant EMI shielding design with vertical thermal pathway engineering. A layered polymer–MXene composite structure was adapted to shift the shielding mechanism from conventional reflection-dominated behavior to controlled electromagnetic absorption through impedance matching, dielectric–magnetic interactions, and multiple internal reflection. This approach mitigates secondary electromagnetic pollution and supports next generation wearable, automotive, and aerospace electronics. Simultaneously, thermally conductive fillers were incorporated into MXene interlayer voids to form 3D multidirectional heat-transfer networks, overcoming the intrinsic in-plane-dominant thermal transport of MXene films. By enabling efficient out of plane heat dissipation during electromagnetic attenuation, the resulting anisotropy-engineered structure prevents localized heating and ensures stable, multifunctional operation under high-frequency and high-power conditions.