Jingjing Jia

Highly Aligned Graphene/Polymer Nanocomposites with Excellent Dielectric Properties for High-Performance Electromagnetic Interference Shielding

Nanocomposites that contain reinforcements with preferred orientation have attracted significant attention because of their promising applications in a wide range of multifunctional fields. Many efforts have recently been focused on developing facile methods for preparing aligned graphene sheets in solvents and polymers because of their fascinating properties including liquid crystallinity and highly anisotropic characteristics. Self-aligned in situ reduced graphene oxide (rGO)/polymer nanocomposites are prepared using an all aqueous casting method. A remarkably low percolation threshold of 0.12 vol% is achieved in the rGO/epoxy system owing to the uniformly dispersed, monolayer graphene sheets with extremely high aspect ratios (>30000). The self-alignment into a layered structure at above a critical filler content induces a unique anisotropy in electrical and mechanical properties due to the preferential formation of conductive and reinforcing networks along the alignment direction. Accompanied by the anisotropic electrical conductivities are exceptionally high dielectric constants of over 14000 with 3 wt% of rGO at 1 kHz due to the charge accumulation at the highly-aligned conductive filler/insulating polymer interface according to the Maxwell-Wagner-Sillars polarization principle. The highly dielectric rGO/epoxy nanocomposites with the engineered structure and properties present high performance electromagnetic interference shielding with a remarkable shilding efficiency of 38 dB.

Graphene Oxide-Based Amplified Fluorescent Biosensor for Hg2+ Detection through Hybridization Chain Reactions

We report a graphene oxide (GO)-based fluorescent sensor for Hg(2+) detection in aqueous solutions by using hybridization chain reactions (HCRs). GO is used as an adsorption material for capturing single-stranded DNA and an efficient fluorescence quencher for reducing the background signal. In the detection strategy, two hairpin probes and a helper DNA are employed. Without Hg(2+), they are adsorbed by the GO and the fluorescence of one of the hairpin probes is quenched. In the presence of Hg(2+), the HCRs between the two hairpin probes are initiated by Hg(2+) with the aid of the helper DNA through T-Hg(2+)-T coordination chemistry. The double-stranded DNA products of the HCRs are released by the GO and the fluorescence is recovered. The detection limit of the sensing method is 0.3 nM, which is sufficiently sensitive for practical applications. The sensing system also exhibits high selectivity against other divalent metal ions, and the application of the sensor for drinking water shows that the proposed method works well for real samples.

Enhancement of mechanical properties of natural fiber composites via carbon nanotube addition

The effects of carbon nanotubes (CNTs) on the mechanical and fracture properties of ramie fiber-reinforced epoxy composites were investigated. Three-point bending, short beam shear, single-edge-notch bending, and Charpy impact tests were employed to evaluate the properties of ramie fiber-reinforced composites without and with CNTs modification. The fracture mechanisms were revealed with the aid of the dynamic mechanical analysis, Fourier transform infrared, and X-ray photoelectron spectroscopy. It was found that the mechanical and fracture properties of ramie fiber-reinforced composites were enhanced by incorporating multiwalled carbon nanotubes, except the impact fracture toughness. The unique chemical compositions and the multiscaled nanosized microstructures of natural fibers brought into focus new mechanisms for the improvement of the mechanical properties of natural fiber-reinforced composites.

Highly transparent conducting graphene films produced by langmuir blodgett assembly as flexible electrodes

This paper reports the development of an efficient method to produce transparent conductive graphene films layer-by-layer on a flexible substrate based on the Langmuir Blodgett (LB) assembly technique. Monolayer ultralarge graphene oxide (UL-GO) sheets of average lateral size greater than 300 µm2 are prepared by repeated centrifugation of as-prepared GO aqueous dispersion. GO films having different numbers of GO layers are fabricated using the LB method while controlling the LB trough surface pressure and pulling speed of the substrate from the dispersion. GO films are chemically reduced at 90°C using hydrogen iodide (HI) acid, followed by chemical doping treatments. The sheet resistance values of the graphene thin films on a PET film are 1.8 and 1.1 kΩ/sq for 2 and 4 graphene layers, respectively, with a transparency of higher than 90%, which are sufficient for many useful applications. It is found that the thicker the film, the higher the conductivity; and vice versa for the transparency of the graphene films.