Yajun Zhang,Long Pan,Xin Cao,Peigen Zhang,ZhengMing Sun
Gradient structures are effective for microwave absorbing but suffer from inadequate lightweight and poor flexibility, making them fall behind the comprehensive requirements of electromagnetic protection. Herein, we propose a hierarchical gradient structure by integration with porous and sandwich structures. Specifically, polyimide (PI) foams are used as a robust and flexible skeleton, in which the foam cell walls are sandwiched by Ti3C2Tx, ZnO, and ZrO2 atomic layers in sequence. Owing to the decreasing conductivity of Ti3C2Tx, ZnO, and ZrO2, they form gradient impedance matching layers on both sides of the PI foam cell walls, significantly enhancing the absorbing intensity for microwaves. In addition, the porous and sandwich structures can synergistically facilitate multiple reflections, increasing the number of interactions between microwave and foam cell walls. Therefore, the resulting lightweight ZrO2@ZnO@Ti3C2Tx@PI (ZrZnTP) composite foams reach a minimum reflection loss of −68.4 dB with an effective absorbing bandwidth covering the whole X band (8.2–12.4 GHz). The ZrZnTP also exhibits outstanding flexibility even at an extremely low temperature of −196 °C (i.e., liquid nitrogen). This work offers a general approach to realizing hierarchically integrated structures of gradient, porousness, and sandwich structures for lightweight, flexible, broadband, and strong microwave absorbing materials.
Driven by the increasing integration and higher power requirements of electronics, polymer-based composites with high-performance in terms of thermal conductivity (TC) and electromagnetic (EM) wave absorption have become an important issue. Herein, multi-layer boron nitride-carbon nanotube/carboxymethyl cellulose/polydimethylsiloxane (BN–CNT/CMC/PDMS) composites with enhanced interface interactions and continuous thermal pathways with gradient impedance were manufactured through a strategy involving chemical surface modification, directional freeze casting, freeze drying and matrix infiltration. Benefiting from the covalent bonding effect between fillers as well as the consecutive thermal conductive pathways, the obtained composites achieved a maximum through-plane TC of 3.56 W m K−1 at a filler content of only 8 wt%. Meanwhile, the composites also achieved an ultra-wide effective electromagnetic wave absorption bandwidth (EMB) of 13.45 GHz, which was attributed to the precisely controllable electromagnetic parameters and the gradient impedance structures. Therefore, these results fully indicate that the composites have great application potential as packaging materials for advanced electronics.
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