Designable Electrical/Thermal Coordinated Dual-Regulation Based on Liquid Metal Shape Memory Polymer Foam for Smart Switch

Multifunctional Liquid-Metal Composites for Electromagnetic Communication and Attenuation

Efficient and reliable information transmission is crucial in the widespread use of electronic products and wireless communication. Additionally, it is vital to address the electromagnetic interference (EMI) and radiation that arise from the communication process. In particular, the emergence of flexible electronic products has posed new hurdles for EM functional materials with flexibility and high performance. Liquid metal (LM) is an innovative EM functional material that possesses both the conductivity of metals and the fluidity to reconfigure like a liquid. These characteristics paved the way for developing novel flexible electronic devices and products. This review provides an overview of the current status and future potential of LM-based EM functional materials. It highlights the latest progress in LM-based materials for applications such as EMI shielding, EM-wave absorption, and wireless communication (antennas). Finally, the primary obstacles of LM-based EM functional materials are discussed and revealed potential directions for their advancement. Overall, the current research on LM-based EM functional materials indicates that they have great potential to promote the development of EM functional materials, thus providing new possibilities for the advancement of flexible electronic products.

Multifunctional Stimuli-Responsive Polyaniline-Based Conductive Composite Film

There is a growing demand for multifunctional materials that can meet the increasingly complex needs of modern society. The combination of functionalization and intellectualization promotes the development of multifunctional smart materials. These materials are not only required to possess excellent basic properties, but also need to integrate multiple functions to adapt to various application scenarios. In this study, a simple solution co-blending method for preparing a polyaniline-based multifunctional conductive composite film was proposed. This methodology employs polyvinyl alcohol (PVA) as a stimuli-responsive matrix, combined with polyaniline (PANI) serving as a functional component, while glutaraldehyde (GA) acts as the crosslinking agent. This PANI-based composite film overcomes the disadvantage that PANI does not easily form a uniform film. The maximum conductivity of this film can reach 0.034 S·cm-1. It is worth noting that the combination of PANI with the stimuli-responsive PVA film resulted in a composite film that not only retained good electrical conductivity, but also exhibited multiple stimuli-responsive properties. These stimuli-responsive properties can be controlled by external stimuli such as heat, voltage, light, or water. The PANI-based composite film could recover its original shape within 25 s when the applied voltage reached 30 V. These characteristics open up possibilities of potential applications where controlled deformation is desired.

Inter-Skeleton Conductive Routes Tuning Multifunctional Conductive Foam for Electromagnetic Interference Shielding, Sensing and Thermal Management

Conductive polymer foam (CPF) with excellent compressibility and variable resistance has promising applications in electromagnetic interference (EMI) shielding and other integrated functions for wearable electronics. However, its insufficient change amplitude of resistance with compressive strain generally leads to a degradation of shielding performance during deformation. Here, an innovative loading strategy of conductive materials on polymer foam is proposed to significantly increase the contact probability and contact area of conductive components under compression. Unique inter-skeleton conductive films are constructed by loading alginate-decorated magnetic liquid metal on the polymethacrylate films hanged between the foam skeleton (denoted as AMLM-PM foam). Traditional point contact between conductive skeletons under compression is upgraded to planar contact between conductive films. Therefore, the resistance change of AMLM-PM reaches four orders of magnitude under compression. Moreover, the inter-skeleton conductive films can improve the mechanical strength of foam, prevent the leakage of liquid metal and increase the scattering area of EM wave. AMLM-PM foam has strain-adaptive EMI shielding performance and shows compression-enhanced shielding effectiveness, solving the problem of traditional CPFs upon compression. The upgrade of resistance response also enables foam to achieve sensitive pressure sensing over a wide pressure range and compression-regulated Joule heating function.

Magneto-Dielectric Synergy and Multiscale Hierarchical Structure Design Enable Flexible Multipurpose Microwave Absorption and Infrared Stealth Compatibility

Developing advanced stealth devices to cope with radar-infrared (IR) fusion detection and diverse application scenarios is increasingly demanded, which faces significant challenges due to conflicting microwave and IR cloaking mechanisms and functional integration limitations. Here, we propose a multiscale hierarchical structure design, integrating wrinkled MXene IR shielding layer and flexible Fe3O4@C/PDMS microwave absorption layer. The top wrinkled MXene layer induces the intensive diffuse reflection effect, shielding IR radiation signals while allowing microwave to pass through. Meanwhile, the permeable microwaves are assimilated into the bottom Fe3O4@C/PDMS layer via strong magneto-electric synergy. Through theoretical and experimental optimization, the assembled stealth devices realize a near-perfect stealth capability in both X-band (8-12 GHz) and long-wave infrared (8-14 µm) wavelength ranges. Specifically, it delivers a radar cross-section reduction of - 20 dB m2, a large apparent temperature modulation range (ΔT = 70 °C), and a low average IR emissivity of 0.35. Additionally, the optimal device demonstrates exceptional curved surface conformability, self-cleaning capability (contact angle ≈ 129°), and abrasion resistance (recovery time ≈ 5 s). This design strategy promotes the development of multispectral stealth technology and reinforces its applicability and durability in complex and hostile environments.

Lightweight Dual-Functional Segregated Nanocomposite Foams for Integrated Infrared Stealth and Absorption-Dominant Electromagnetic Interference Shielding

Lightweight infrared stealth and absorption-dominant electromagnetic interference (EMI) shielding materials are highly desirable in areas of aerospace, weapons, military and wearable electronics. Herein, lightweight and high-efficiency dual-functional segregated nanocomposite foams with microcellular structures are developed for integrated infrared stealth and absorption-dominant EMI shielding via the efficient and scalable supercritical CO2 (SC-CO2) foaming combined with hydrogen bonding assembly and compression molding strategy. The obtained lightweight segregated nanocomposite foams exhibit superior infrared stealth performances benefitting from the synergistic effect of highly effective thermal insulation and low infrared emissivity, and outstanding absorption-dominant EMI shielding performances attributed to the synchronous construction of microcellular structures and segregated structures. Particularly, the segregated nanocomposite foams present a large radiation temperature reduction of 70.2 °C at the object temperature of 100 °C, and a significantly improved EM wave absorptivity/reflectivity (A/R) ratio of 2.15 at an ultralow Ti3C2Tx content of 1.7 vol%. Moreover, the segregated nanocomposite foams exhibit outstanding working reliability and stability upon dynamic compression cycles. The results demonstrate that the lightweight and high-efficiency dual-functional segregated nanocomposite foams have excellent potentials for infrared stealth and absorption-dominant EMI shielding applications in aerospace, weapons, military and wearable electronics.

Ultrasensitive Ionic Conductors with Tunable Resistance Switching Temperature Enabled by Phase Transformation of Polymer Cocrystals

Phase-transformable ionic conductors (PTICs) show significant prospects for functional applications due to their reversible resistance switching property. However, the representative design principle of PTICs is utilizing the melt-crystallization transition of ionic liquids, and the resistance switching temperatures of such PTICs cannot be tuned as desired. Herein, a new strategy is proposed to design PTICs with on-demand resistance switching temperatures by using the melt-crystallization transition of polymer cocrystal phase, whose melting temperature shows a linear relationship with the polymer compositions. Owing to the melt of polymer cocrystal domains and the tunable migration of ions in the resistance switching region, the obtained PTICs display ultrahigh temperature sensitivity with a superior temperature coefficient of resistance of -8.50% °C-1 around human body temperature, as compared to various ionic conductors previously reported. Therefore, the PTICs can detect tiny temperature variation, allowing for the intelligent applications for overheating warning and heat dissipation. It is believed that this work may inspire future researches on the development of advanced soft electrical devices.

Liquid Metal-Polymer Conductor-Based Conformal Cyborg Devices

Gallium-based liquid metal (LM) exhibits exceptional properties such as high conductivity and biocompatibility, rendering it highly valuable for the development of conformal bioelectronics. When combined with polymers, liquid metal-polymer conductors (MPC) offer a versatile platform for fabricating conformal cyborg devices, enabling functions such as sensing, restoration, and augmentation within the human body. This review focuses on the synthesis, fabrication, and application of MPC-based cyborg devices. The synthesis of functional materials based on LM and the fabrication techniques for MPC-based devices are elucidated. The review provides a comprehensive overview of MPC-based cyborg devices, encompassing their applications in sensing diverse signals, therapeutic interventions, and augmentation. The objective of this review is to serve as a valuable resource that bridges the gap between the fabrication of MPC-based conformal devices and their potential biomedical applications.