Graphene sheets (one-atom-thick, two-dimensional layers of sp2-bonded carbon) are predicted to have a range of unusual properties. Recent studies have shown that individual graphene sheets have extraordinary electrical properties, but an efficient method of graphite exfoliation remains a challenge. A number of approaches to exfoliation have been tried, such as rubbing graphite or using adhesive tape to separate the layers, but these methods are unlikely ever to provide sufficient quantities of material for applications. In this work, two potential applications of graphene-based sheets have been investigated, namely nanocomposites, and graphene-based paper. Electrical measurements were made on the nanocomposites to elucidate their electrical properties. Since it was necessary to take measurements on terraohm impedances at low temperatures down to 10K, a custom cryostat insert with exceptionally low leakage current had to be designed and fabricated. This is described. Composite materials were prepared by using a solution-based chemical approach, exfoliating graphite oxide into individual, chemically-modified graphene sheets embedded in a polystyrene matrix. Composites prepared by the solution-based approach were found to be electrically conductive even when using very small amounts of graphene-based filler; reaching a room-temperature conductivity of 10-6Sm-1 with a graphene-based sheet concentration of 0.15%, the lowest concentration that was measured. The conductivity of the composite was found to depend not only on the concentration of graphene-based filler in the composite, but also on the mechanical and thermal history of the material, which could render the composite completely insulating. It has been shown that conduction within the composite takes place by a variable range hopping mechanism; and the dependence of the conductivity on the processing of the material is most likely due to the morphology of the polymer in which the graphene-based sheets are embedded.

Last modified

• 08/02/2018

Creator

• Geoffrey Hugh Brett Dommett

DOI

• https://doi.org/10.21985/N2DT5D

Subject

• Physics and Astronomy

Keyword

• graphene
• graphite oxide
• high impedance resistance
• nanocomposite
• variable range hopping
• polystyrene

Date created

• 2007-06-01

Resource type

• Dissertation

Rights statement

• In Copyright