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Coupling agent-functionalized boron nitride (f-BN) and glycidyl methacrylate-grafted graphene (g-TrG) are simultaneously blended with polyimide (PI) to fabricate a flexible, electrically insulating and thermally conductive PI composite film. The silk-like g-TrG successfully fills in the gap between PI and f-BN to complete the thermal conduction network. In addition, the strong interaction between surface functional groups on f-BN and g-TrG contributes to the effective phonon transfer in the PI matrix. The thermal conductivity (TC) of the PI/f-BN composite films containing additional 1 wt % of g-TrG is at least doubled to the value of PI/f-BN and as high as 16 times to that of the pure PI. The hybrid film PI/f-BN-50/g-TrG-1 exhibits excellent flexibility, sufficient insulating property, the highest TC of 2.11 W/mK, and ultralow coefficient of thermal expansion of 11 ppm/K, which are perfect conditions for future flexible substrate materials requiring efficient heat dissipation.

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Polyimide (PI) nanocomposites with both enhanced thermal conductivity and dimensional stability were achieved by incorporating glycidyl methacrylate‐grafted graphene oxide (g‐GO) in the PI matrix. The PI/g‐GO nanocomposites exhibited linear enhancement in thermal conductivity when the amount of incorporated g‐GO was less than 10 wt%. With the addition of 10 wt% of g‐GO to PI (PI/g‐GO‐10), the thermal conductivity increased to 0.81 W m−1 K−1 compared to 0.13 W m−1 K−1 for pure PI. Moreover, the PI/g‐GO‐10 composite exhibited a low coefficient of thermal expansion (CTE) of 29 ppm °C−1. The values of CTE and thermal conductivity continuously decreased and increased, respectively, as the g‐GO content increased to 20 wt%. Combined with excellent thermal stability and high mechanical strength, the highly thermally conducting PI/g‐GO‐10 nanocomposite is a potential substrate material for modern flexible printed circuits requiring efficient heat transfer capability.

One primary challenge in nanotoxicology studies is the lack of well-characterised nanoparticle reference materials which could be used as positive or negative nanoparticle controls. The National Institute of Standards and Technology (NIST) has developed three gold nanoparticle (AuNP) reference materials (10, 30 and 60 nm). The genotoxicity of these nanoparticles was tested using HepG2 cells and calf-thymus DNA. DNA damage was assessed based on the specific and sensitive measurement of four oxidatively-modified DNA lesions (8-hydroxy-2´-deoxyguanosine, 8-hydroxy-2´-deoxyadenosine, (5´S)-8,5´-cyclo-2´-deoxyadenosine and (5´R)-8,5´-cyclo-2´-deoxyadenosine) using liquid chromatography/tandem mass spectrometry. Significantly elevated, dose-dependent DNA damage was not detected at concentrations up to 0.2 μg/ml, and free radicals were not detected using electron paramagnetic resonance spectroscopy. These data suggest that the NIST AuNPs could potentially serve as suitable negative-control nanoparticle reference materials for in vitro and in vivo genotoxicity studies. NIST AuNPs thus hold substantial promise for improving the reproducibility and reliability of nanoparticle genotoxicity studies.

A facile technique was developed to improve the water barrier properties of transparent polyimide (PI) films. Transparent and organo‐soluble PI films were synthesized from an alicyclic tetracarboxylic dianhydride (bicyclo[2.2.2]oct‐7‐ene‐2,3,5,6‐tetracarboxylic dianhydride) and an aromatic diamine (3,4′‐oxydianiline) in a co‐solvent of dimethylacetamide (DMAc) and γ‐butyrolactone via a one‐step process. Thermally reduced graphene (RG) was then blended with the PI in DMAc solution to fabricate PI/RG nanocomposite films without the addition of coupling agent. With the incorporation of only 0.1 wt% highly exfoliated RG in the PI matrix, the resultant PI/RG‐0.1 nanocomposite exhibited a superior barrier to moisture and retained high transmittance in the visible light region. The surface of PI/RG was more hydrophobic than that of pure PI and simultaneously the water vapor transmission rate was significantly reduced to 13 g m−2 day−1 for the PI/RG‐0.1 nanocomposite compared to 181 g m−2 day−1 for pure PI. Notably, the PI/RG‐0.1 nanocomposite also exhibited favorable thermal stability with a lower coefficient of thermal expansion and a higher thermal degradation temperature compared to pure PI. The easy processing of PI solution and RG nanosheets, the good orientation of RG in PI and the excellent barrier and thermal properties of PI/RG make the transparent PI nanocomposite films potential substrate materials in flexible electronic applications.