Magnetodielectric effect of Graphene-PVA Nanocomposites

Graphene-Polyvinyl alcohol (PVA) nanocomposite films with thickness $120 \mu m$ were synthesized by solidification of PVA in a solution with dispersed graphene nanosheets. Electrical conductivity data were explained as arising due to hopping of carriers between localized states formed at the graphene-PVA interface. Dielectric permittivity data as a function of frequency indicated the occurrence of Debye-type relaxation mechanism. The nanocomposites showed a magnetodielectric effect with the dielectric constant changing by 1.8% as the magnetic field was increased to 1 Tesla. The effect was explained as arising due to Maxwell-Wagner polarization as applied to an inhomogeneous two-dimensional,two-component composite model. This type of nanocomposite may be suitable for applications involving nanogenerators.Comment: 13 pages, 11 figure

Effect of Water Vapor on Electrical Properties of Individual Reduced Graphene Oxide Sheets

The electrical conductivity and gas-sensing characteristics of individual sheets of partially reduced graphene oxide are studied, and the results display a strong dependence on the chosen reduction method. Three reduction procedures are considered here: thermal, chemical, and a combined chemical/thermal approach. Samples treated by chemical/thermal reduction display the highest conductivity whereas thermally reduced samples display the fastest gas-sensing response times. The chemo-resistive response to water vapor adsorption is well fit by a linear driving force model. The conductivity upon exposure to water vapor and measured as a function of the gated electric field displays significant hysteresis. These results illustrate how the chemical structure of graphene oxide may be tailored to optimize specific properties for applications such as field effect devices and gas sensors

Graphene oxide papers modified by divalent ions - Enhancing mechanical properties via chemical cross-linking

Significant enhancement in mechanical stiffness (10-200%) and fracture strength (similar to 50%) of graphene oxide paper, a novel paperlike material made from individual graphene oxide sheets, can be achieved upon modification with a small amount (less than 1 wt %) of Mg2+ and Ca2+. These results (an be readily rationalized in terms of the chemical interactions between the functional groups of the graphene oxide sheets and the divalent metals ions. While oxygen functional groups on the basal planes of the sheets and the carboxylate groups on the edges can both bond to Mg2+ and Ca2+, the main contribution to mechanical enhancement of the paper comes from the latter

Chemical structures of hydrazine-treated graphene oxide and generation of aromatic nitrogen doping

Chemically modified graphene platelets, produced via graphene oxide, show great promise in a variety of applications due to their electrical, thermal, barrier and mechanical properties. Understanding the chemical structures of chemically modified graphene platelets will aid in the understanding of their physical properties and facilitate development of chemically modified graphene platelet chemistry. Here we use C-13 and N-15 solid-state nuclear magnetic resonance spectroscopy and X-ray photoelectron spectroscopy to study the chemical structure of N-15-labelled hydrazine-treated C-13-labelled graphite oxide and unlabelled hydrazine-treated graphene oxide, respectively. These experiments suggest that hydrazine treatment of graphene oxide causes insertion of an aromatic N-2 moiety in a five-membered ring at the platelet edges and also restores graphitic networks on the basal planes. Furthermore, density-functional theory calculations support the formation of such N-2 structures at the edges and help to elucidate the influence of the aromatic N-2 moieties on the electronic structure of chemically modified graphene platelets