We demonstrate that ultralight carbon aerogels with skeletal densities lesser than the air density can levitate in air, based on Archimedes' principle, when heated with light. Porous materials, such as aerogels, facilitate the fabrication of materials with density less than that of air. However, their apparent density increases because of the air inside the materials, and therefore, they cannot levitate in air under normal conditions. Ultralight carbon aerogels, fabricated using carbon nanotubes, have excellent light absorption properties and can be quickly heated by a lamp owing to their small heat capacity. In this study, an ultralight carbon aerogel was heated with a halogen lamp and levitated in air by expanding the air inside as well as selectively reducing its density. We also show that the levitation of the ultralight carbon aerogel can be easily controlled by turning the lamp on and off. These findings are expected to be useful for various applications of aerogels, such as in communication and transportation through the sky.
Ultralight materials exhibit superelastic behavior depending on the selection, blending, and carbonization of the materials. Recently, ultimate low-density materials of 5 mg/cm3 or less have attracted attention for applications such as sensors, electrodes, and absorbing materials. In this study, we fabricated an ultralight material composed of single-walled carbon nanotubes (CNT) and sodium carboxymethyl cellulose (CMC), and we investigated the effect of density, composition, and weight average molecular weight of CMC on elastic recovery properties of ultralight CNT/CMC composites. Our results showed that the elastic recovery properties can be improved by reducing the density of the composite, lowering the mass ratio of CNTs, and using CMC with small molecular weight.
In this paper, we report ultralight carbon-nanotube (CNT)-infused materials with high electromagnetic shielding and absorption performance over an ultrabroadband frequency range. By controlling the CNT content and thickness of ultralight aerogels composed of CNTs during fabrication, their electromagnetic shielding/absorbing performance can be tuned over a wide frequency range (5.6–110 GHz). Samples with 40 wt% CNTs exhibit excellent shielding performance in an intensity range of 30–90 dB in all frequency ranges. Samples with less than 5 wt% CNTs show improved electromagnetic wave absorption performance of more than 10 dB. In addition, in samples with 2 and 4 wt% CNTs, strong absorption of over 25 dB occurs at certain frequencies. These CNT aerogels, which are ultralight (bulk density: 10 mg cm−3) and exhibit good mechanical properties, are expected to become a new material for electromagnetic shielding and absorption in advanced engineering applications.
Absorbing low-frequency sound below 1000 Hz with an ultralight material is a critical challenge. Nanofibrous sound-absorbing materials have many interfaces for air-borne sound loss. In addition, nanofibers with a high elastic modulus can increase the loss of sound propagating in the solid, enabling good, lowfrequency sound absorption. Herein, a composite aerogel based on singlewalled carbon nanotubes (SWCNTs) and carboxymethyl cellulose (CMC) as an ultralight material that effectively absorbs low-frequency sound is reported. This ultralight aerogel has a hierarchical porous structure composed of highmodulus SWCNT-CMC composite nanofibers. A sample with an areal density of 20 mg cm À2 (bulk density: 5 mg cm À3 , thickness: 39 mm) achieves a soundabsorption coefficient of 0.44 at 500 Hz. The sound-absorption behavior is sufficiently described by the Biot-Johnson-Champoux-Allard model, indicating the significant effect of the high elastic modulus of the nanofibers on the soundabsorption performance. The article presents a new design principle for ultralight materials with low-frequency sound absorption that takes into consideration both the porous structure and the elastic modulus of the material framework.
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