Ultralight and Flexible Polyurethane/Silver Nanowire Nanocomposites with Unidirectional Pores for Highly Effective Electromagnetic Shielding

Abstract

Flexible waterborne polyurethane (WPU)/silver nanowire (AgNW) nanocomposites with unidirectionally aligned micrometer-sized pores are fabricated using a facile freeze-drying process, and their dimensions, densities, and AgNW contents are easily controllable. The high-aspect-ratio AgNWs are well-dispersed in the nanocomposite cell walls, giving the nanocomposites good compression strength and excellent electrical conductivity even at very low densities. The large conductivity mismatch between the AgNWs and WPU also induces substantial interfacial polarization that benefits the absorption of electromagnetic (EM) waves, whereas the aligned cell walls promote multireflections of the waves in the porous architectures, further facilitating the absorption. The synergistic actions of the AgNWs, WPU, and unidirectionally aligned pores lead to ultrahigh EM shielding performance. The X-band shielding effectiveness (SE) of the nanocomposites is 64 and 20 dB at the densities of merely 45 and 8 mg/cm³, respectively, and ultrahigh surface specific SE of ∼1087 dB cm³/(g mm) is achieved with only 0.027 vol % AgNWs, demonstrating that they are promising ultralight, flexible, mechanically robust, high-performance EM shielding materials.