I-Hsiang Tseng

Flexible Polyimide Films Hybrid with Functionalized Boron Nitride and Graphene Oxide Simultaneously To Improve Thermal Conduction and Dimensional Stability

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.

NIST gold nanoparticle reference materials do not induce oxidative DNA damage

Abstract 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.

Flexible and Transparent Polyimide Films Containing Two-Dimensional Alumina Nanosheets Templated by Graphene Oxide for Improved Barrier Property

Unique two-dimensional alumina nanosheets (Alns) using graphene oxide (GO) as templates are fabricated and successfully incorporated with organo-soluble polyimide (PI) to obtain highly transparent PI nanocomposite films with improved moisture barrier property. The effects of filler types and contents on water vapor transmission rate (WVTR) and transparency of PI are systematically studied. The hydroxyl groups on GO react with aluminum isopropoxide via sol-gel process to obtain alumina coverd-GO (Al-GO), and then thermal decomposition is applied to obtain Alns. Alns are the most efficient fillers among others to restrict the diffusion of water vapor within PI matrix and simultaneously maintain the transparency of PI. XRD pattern, TEM, and AFM images confirm the sheet-like morphology of Alns with ultrahigh aspect ratio. With only 0.01 wt % of Alns, the PI nanocomposite film exhibits the most significant reduction of 95% in WVTR as compared to that of pure PI film. Most importantly, the resultant PI/Alns-0.01 film exhibits excellent optical transparency and high mechanical strength and great thermal stability.

Composition, thermal and tensile properties of polyurethane-urea-silica hybrids

Polyurethane-Urea-Silica (PUUS) hybrid solutions were synthesized by a two-stage process, based on the use of polyoxypropylene glycol (PPG), 4,4′-dicyclohexyl methane diisocyanate (H12MDI), 1,4-butane diol, 3-aminopropyl-trimethoxysilane (APrTMOS) and a suitable amount of solvent. Following knife-coating and curing reaction, polyurethane/urea/silica hybrid films were prepared with different crosslinkages and silica contents through the in situ sol–gel process. The intermolecular bonding of hydrogen bonding between N–H, CO groups of PU and area and Si–O–Si crosslinked structure of APrTMOS was determined via FTIR analysis, and was correlated with thermal/tensile properties. FTIR and ESCA results indicate that the carbonyl, N–H and Si–O groups distribution contained in PU and hybrid films characterized as CO group absorption peak area ratio, N/C and Si/C atomic ratio were changed from the films surface to the bulk with APrTMOS content. Intermolecular bonding, composition, thermal property and tensile strength of films were functions of the APrTMOS contents and PPGs molecular weight. All hybrid films exhibit a more significant change in glass transition temperature (Tg), decomposition temperatures (Td), coefficients of thermal expansion (CTEs) and stress-strain properties than that with pure PUs. The correlation between intermolecular bonding, composition, thermal and tensile properties were investigated.

Pigment and nanofiller photoreactivity database

The service life and durability of nanocomposites containing fillers are affected by photocatalytic properties of these fillers, particularly narrow band gap metal oxides (NBMOs) such as titanium dioxide (TiO2). When irradiated with ultraviolet flux, NBMOs produce electrons and other species that are capable of causing rapid degradation of organic materials with which they are in contact. Electrons and holes (positively charged species) migrate to the surface and react with species to generate various free radicals. Measurement science tools for characterizing TiO2 photoreactivity using electron paramagnetic resonance (EPR) methods have been developed by the Engineering Laboratory (EL) at the National Institute of Standards and Technology (NIST) and a linkage between EPR measurements and current industrial methods has been established. A database of TiO2 photoreactivity values and other data measured via the EPR methods and industrial assays has been compiled and will be accessed through a searchable software database in the NIST Standard Reference Database program—http://www.nist.gov/srd/index.cfm. The database provides fundamental photoreactivity data that can be used for product selection and development purposes to enable more reliable assessments of end-performance.