分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-05-02
Li, Y [Li, Yang][ 1 ]
Shen, B [Shen, Bin][ 1 ]
Pei, XL [Pei, Xueliang][ 2 ]
Zhang, YG [Zhang, Yonggang][ 2 ]
Yi, D [Yi, Da][ 3 ]
Zhai, WT [Zhai, Wentao][ 1 ]
Zhang, LH [Zhang, Lihua][ 1 ]
Wei, XC [Wei, Xingchang][ 3 ]
Zheng, WG [Zheng, Wenge][ 1 ]
摘要： Ultrathin carbon foams with the thickness about 24 mm were fabricated by the pyrolysis of polyimide/ graphene composite foams. The addition of graphene was verified to stabilize the porous structure of the foams and accelerate their graphitization process simultaneously. Consequently, the well-defined carbon foams exhibited much higher electromagnetic interference (EMI) shielding effectiveness (SE) up to 24 dB over the frequency range of 8e12 GHz, in comparison with the non-foamed counterparts. The possible mechanism behind the phenomenon was attributed to their enhanced microwave absorption via the internal multiple scattering and reflections. Moreover, the SE could be further improved to 43 and 51 dB by increasing the sample thickness gradually to 51 and 73 mm, respectively. The carbon foams with high thermal stability are very promising in the fabrication of ultrathin EMI shields for thermally harsh applications.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-05-02
摘要： In this study, highly cross-linked and completely imidized polyimide aerogels were prepared from polyimide containing trimethoxysilane side groups, which was obtained as the condensation product of polyimide containing acid chloride side groups and 3-aminopropyltrimethoxysilane. After adding water and acid catalyst, the trimethoxysilane side groups hydrolyzed and condensed one another, and a continuous increase in the complex viscosities of the polyimide solutions with time was observed. The formed polyimide gels were dried by freeze-drying from tert-butyl alcohol to obtain polyimide aerogels, which consisted of a three-dimensional network of polyimide fibers tangled together. By varying the solution concentration of the polyimide containing trimethoxysilane side groups, polyimide aerogels with different densities (ranging from 0.19 to 0.42 g/cm3) were obtained. The resulting polyimide aerogels had small pore diameter (ranging from 20.7 to 58.3 nm), high surface area (ranging from 310 to 344 m2/g), high 5% weight loss temperature in air (at about 440 °C), and an excellent mechanical property. In addition, the glass transition temperature (349 °C) of the polyimide aerogels was much higher than that (210 °C) of the corresponding linear polyimide. So, even after being heated at 300 °C for 30 min, the porous structure of the polyimide aerogels was not completely destroyed.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-05-02
Shen, B [Shen, Bin][ 1 ]
Li, Y [Li, Yang][ 1 ]
Zhai, WT [Zhai, Wentao][ 1 ]
Zheng, WG [Zheng, Wenge][ 1 ]
摘要： The fabrication of low-density and compressible polymer/graphene composite (PGC) foams for adjustable electromagnetic interference (EMI) shielding remains a daunting challenge. Herein, ultralightweight and compressible PGC foams have been developed by simple solution dip-coating of graphene on commercial polyurethane (PU) sponges with highly porous network structure. The resultant PU/graphene (PUG) foams had a density as low as ∼0.027−0.030 g/cm3 and possessed good comprehensive EMI shielding performance together with an absorption-dominant mechanism, possibly due to both conductive dissipation and multiple reflections and scattering of EM waves by the inside 3D conductive graphene network. Moreover, by taking advantage of their remarkable compressibility, the shielding performance of the PUG foams could be simply adjusted through a simple mechanical compression, showing promise for adjustable EMI shielding. We believe that the strategy for fabricating PGC foams through a simple dip-coating method could potentially promote the large-scale production of lightweight foam materials for EMI shielding.
提交时间： 2017-05-02
Shen, B [Shen, Bin][ 1 ]
Li, Y [Li, Yang][ 1 ]
Yi, D [Yi, Da][ 2 ]
Zhai, WT [Zhai, Wentao][ 1 ]
Wei, XC [Wei, Xingchang][ 2 ]
Zheng, WG [Zheng, Wenge][ 1 ]
摘要： As reported, the foaming of layered graphene films into porous graphene foams could improve their performance for absorbents, catalysis and supercapacitors. Herein, to emphasize the impact of porous structure on electromagnetic interference [EMI] shieldin
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-05-02
Pei, XL [Pei, Xueliang][ 1 ]
Shen, B [Shen, Bin][ 1 ]
Zhang, LH [Zhang, Lihua][ 1 ]
Zhai, WT [Zhai, Wentao][ 1 ]
Zheng, WG [Zheng, Wenge][ 1 ]
摘要： In this article, a composite film from polyimide and thermally exfoliated graphene was prepared through in situ polymer- ization, and the weight percent of thermally exfoliated graphene with respect to the polyimide monomers was 5 wt %. The film was carbonized at 1000 C for 1 h and then heat-treated at various temperatures up to 2100 C. For comparison, the corresponding pure polyimide film was also prepared and heat-treated at the same condition. It was found that the addition of graphene could effectively prevent the polyimide film from shrinking in the direction parallel to the film surface during the heat treatment. Furthermore, the results of density, X-ray diffraction, shrinkage in the direction perpendicular to the film surface and scanning electron microscopy revealed that the graphitization process of the polyimide could be accelerated by addition of graphene obviously. In view of the above phenomena, a reasonable explanation was presented. VC 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41274.
提交时间： 2017-05-02
摘要： As the portable device hardware has been increasing at a noticeable rate, ultrathin thermal conducting materials [TCMs] with the combination of high thermal conductivity and excellent electromagnetic interface [EMI] shielding performance, which are used t
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