Polymer-based aerogels have proven to be a promising choice to obtain high-performance and lightweight materials for electromagnetic microwave (EMW) absorption. Here, directional freeze-drying was used to produce multifunctional ultralight CNTs/PI composite aerogels with oriented microchannel structures. The unique oriented pore structure causes the multiple reflections and scattering of incident EMW inside the material, which favors the attenuation of the EM energy. By changing the CNTs content in the composite aerogels, the dipole polarization and the interface polarization can be effectively regulated. With a CNTs content of 30 % and a thickness of 2.5 mm, the minimum reflection loss (RL min ) of −41 dB was achieved at 15.36 GHz. A large effective absorption bandwidth (EAB) of 6.88 GHz was achieved at a thickness of 3 mm. In addition, the CNTs/PI composite aerogels displayed excellent toughness, thermal isolation and the thermal stability. The high-temperature resistant, lightweight composite aerogels proposed in this study could provide a feasible and effective approach for the development of advanced multifunctional microwave-absorbing materials.
In this study, a simple and cost-effective metal oxide semiconductor (MOS) gas sensor, which can be fabricated utilizing only two photolithography steps, was designed and developed through the planar microelectromechanical systems (MEMS) technique. Ball-milled porous tin dioxide nanoparticle clusters were precisely drop-coated onto the integrated microheater region and subsequently characterized using a helium ion microscope (HIM). The spatial suspension of the silicon nitride platform over the silicon substrate provides superior thermal isolation and thus dramatically reduces the power consumption of the microheater. The well-designed microheater exhibits excellent thermal uniformity, which was verified both computationally and experimentally. The as-fabricated sensors were tested for ethanol gas sensing at various operating temperatures with different concentrations. At the optimal work temperature of ∼400 °C, our gas sensors demonstrated a respectable sensitivity to 1 ppm ethanol, which is the lower detection limit to most commercial products. Moreover, stable performance over repetitive testing was observed. The innovative sensor developed here is a promising candidate for portable gas sensing devices and various other commercial applications.
Radiative cooling provides a supplement to traditional active energy-intense cooling. Recently, photonic designs have emerged to realize efficient daytime radiative cooling (DRC) based on high emission in the mid-infrared and reflectance in the solar spectrum. However, such technologies tend to be costly and suffer from complex processes, which significantly limit their application. Herein, a polyvinylidene difluoride/polyvinylpyrrolidone-(hollow aluminum phosphate microspheres) (PVDF/PVP-(H-AlPO4)) dual-layer composite fiber film was prepared via a straightforward and cost-effective microfluidic electrospinning technique, combining multieffect cooling, including thermal isolation, solar reflection, and a self-pumping process. The incorporation of hollow aluminum phosphate microspheres (H-AlPO4) in the polymer matrix enhances the mechanical properties and overall scattering ability. Promisingly, the PVDF/PVP-(H-AlPO4) dual-layer composite fiber film ensures the desired DRC performance, achieves a high emissivity of 91.46% in the atmospheric window, and reflects 94.76% of the solar radiation. In outdoor environments under 605 W/m2 solar radiation, the dual-layer composite fiber film obtains an average 3.1 °C subambient cooling temperature, with the highest cooling temperature reaching 6.4 °C. We believe that this study not only provides an efficient method for preparing DRC fiber films with photonic structures but also offers a potential solution for the design of radiative cooling materials and lays a solid foundation for its practical application.
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