Date of Completion

7-22-2013

Embargo Period

7-22-2013

Keywords

Graphene, Exfolation, Graphite, Surface Chemistry

Major Advisor

Douglas Adamson

Associate Advisor

Andrey Dobrynin

Associate Advisor

Thomas Seery

Associate Advisor

Montgomery Shaw

Field of Study

Polymer Science

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Graphene, a two-dimensional sheet of atomically thin carbon, has recently gained

attention due to its excellent electronic, mechanical, and optical properties. It has the

potential for use in a variety of applications such as circuits, solar cells, and

transparent conducting electrodes. In order to feasibly produce graphene, practical

methods for its preparation need to be developed. Current methods, such as

micromechanical exfoliation (Scotch tape™), solvent exfoliation and chemical vapor

deposition (CVD) are far from ideal. Micromechanical exfoliation produces minute

amounts of very small graphene flakes, and CVD is expensive and lacks scalability.

This work presented in this thesis focuses on producing graphene sheets from

natural flake graphite. Graphite, composed of stacked graphene sheets, is naturally

available at low costs. Our use of graphite as a source for graphene will allow for the

large-scale production of inexpensive graphene. This thesis presents two

approaches for the preparation of graphene from graphite: chemical modification

and direct exfoliation.

Chemically modifying graphite with oxygen functional groups to form graphite oxide

(GO) increases the interlayer spacing and reduces the van der Waals attractive

forces holding the stacked sheets together. Oxidation increases the water

dispersibility of the graphene and subsequent reduction restores some of the

electrical and mechanical properties of the sheets. We study the oxidation process in

order to optimize the resulting GO material and study the diazonium functionalization

of the dispersed GO. Diazonium salt addition allows for the addition of nitro groups,

increasing the water solubility of the graphene sheets and increasing the processing

options of the sheets.

Direct exfoliation of graphite to graphene sheets is studied using both experimental

and computational techniques. First, we demonstrate the use of an equimolar

mixture of benzene and hexafluorobenzene (B/HFB). This solvent mixture self

assembles into alternating B/HFB stacks due to strong quadrupolar interactions. We

find this stacked morphology can be templated by graphene sheets during

sonication, resulting in order 30 Å from the basal plane of the graphene. This

ordering suspends graphene in solution by preventing re-aggregation and the result

is a suspension of exfoliated, pristine graphene in a highly volatile, easily removable

solvent. A second system, using a water/heptane solvent mixture, is shown stabilize

the graphene sheets at the interface of the phase-separated solvents in order to

minimize interfacial energy. This stabilization is then used to form thin, transparent

and conductive films of graphene as the sheets spread at the interface and climb the

walls of the sample vials.

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