Search

Conventional polyimide nanocomposites reinforced with graphene-based nanofillers usually possess excellent properties, such as high thermal decomposition temperature, enhanced tensile strength, tensile modulus, etc. However, the elongation at break of the nanocomposites is reduced. Here, we prepared N-doped graphene quantum dots/colorless polyimide nanocomposite (N-GQDs/CPI) films for the first time by in-situ polymerization, whose elongation at break is about 2 times that of the pure film. Meanwhile, the thermal properties and other mechanical properties of the films are improved. Through analyzing FT-IR, XPS, XRD, TAG SEM, etc. of N-GQDs and the films, we consider that the strengthening mechanism of matrix performance is attributed to N-GQDs' well dispersion, its small size effects and strong interface interaction with the matrix. Furthermore, at the indicative wavelength of 550 nm, the optical transmittance of the film with 1 wt% N-GQDs still maintains 79%, indicating the resulting films have excellent optical transmittance. The hydrophilic properties of the prepared films' surface is reduced, their water surface contact angle are increased from 63 ± 2.7° to 92 ± 1.7° with the content of N-GQDs increasing. This research shows that N-GQDs can enhance the various properties of polyimide and provides a high performance nanocomposite films for potential flexible substrates. [ABSTRACT FROM AUTHOR]

Abstract: This article described a novel method of preparation of diamond–silicon matrix composites via in situ reaction by spark plasma sintering (SPS). Thermal properties of samples sintered under two conditions (vacuum and argon) were evaluated and the effect of Al-addition to Si matrix was demonstrated. The results presented that Si/diamond composite (sintered in argon) yielded a thermal conductivity (TC) of 346.2W/mK, higher than that of the sample sintered in vacuum, along with a coefficient of thermal expansion (CTE) of 1.455×10−6 K. Microstructures of these materials were studied by scanning electron microscopy and X-ray diffraction. As a result of reaction between diamond and silicon, SiC phase formed. The research showed that the addition of Al could not give any benefit to the thermal conductivity of composite, although it contributed to the relative packing density of 99.6% with a volume fraction of 55% of diamond particles. Additionally, the influence of interface on thermal properties of Si(Al)/diamond composites was specifically discussed. [Copyright &y& Elsevier]