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/cm, respectively, and ultrahigh surface specific SE of ∼1087 dB cm/(g mm) is achieved with only 0.027 vol % AgNWs, demonstrating that they are promising ultralight, flexible, mechanically robust, high-performance EM shielding materials.

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Nanocomposite strain sensors composed of compressed honeycomb-like reduced-graphene-oxide (RGO) foam embedded in polydimethylsiloxane are facilely fabricated via unidirectional freeze-drying and simple mechanical compression. The microstructural characteristics of the nanocomposites endow the sensors with excellent flexibility, high stretchability and sensing sensitivity, as well as anisotropic mechanical and sensing performance when stretched along directions vertical and parallel to the aligned RGO cell walls (defined as transverse and longitudinal directions, respectively). In particular, the compression of the aligned RGO foam into a thinner film results in more conductive pathways, greatly increasing the sensing sensitivity of the nanocomposite sensors. The sensors stretched along the transverse direction show an outstanding combination of high stretchability over 120%, wide linear sensing region of 0-110% and high strain sensing sensitivity with a gauge factor of around 7.2, while even higher strain sensitivity and lower sensing strain are exhibited along the longitudinal direction. Sensitive and reliable detection of human motions is also successfully demonstrated using these light-weight thin-film nanocomposite sensors.

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