Date of Award

12-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

School of Materials Science and Engineering

Committee Member

Igor Luzinov, Committee Chair

Committee Member

George Chumanov

Committee Member

Stephen H. Foulger

Committee Member

Marek Urban

Abstract

Transparent conductive films (TCFs) play a key role in number of devices, including solar panels, LCD/OLED displays and touchscreens. Graphene has emerged as a promising material in this area due to its unique mechanical and electrical properties. Despite noteworthy progress in the fabrication of large-area graphene sheet-like nanomaterials, the vapor-based processing still requires sophisticated equipment and a multistage handling of the material. An alternative approach to manufacturing functional graphene-based films includes the employment of graphene oxide (GO) micron-scale sheets as precursors. However, search for a scalable manufacturing technique for the production of high-quality GO nanoscale films with high uniformity and high electrical conductivity is still continuing. The study presented in this dissertation is dedicated to the fabrication and characterization of electrically conductive films made of reduced graphene oxide sheets (rGO) deposited on both rigid and flexible substrates. Here we show that conventional dip-coating technique can offer fabrication of high quality mono- and bilayered films made of GO sheets. The method is based on our recent discovery that encapsulating individual GO sheets in a nanometer-thick copolymer layer poly(Oligo Ethylene Glycol methyl ether Methacrylate [OEGMA]- Glycidyl Methacrylate [GMA]) allows for the nearly perfect formation of the GO layers on hydrophilic substrates. By thermal reduction at 1000 ⁰C the bilayers (cemented by a carbon-forming polymer linker) are converted into highly conductive and transparent reduced GO films with a high conductivity up to 10000 S/cm and optical transparency on the level of 90%. The value is the highest electrical conductivity reported for thermally reduced nanoscale GO films and is close to the conductivity of indium tin oxide (ITO) currently in use for transparent electronic devices, thus making these layers intriguing candidates for replacement of ITO films. To facilitate the deposition of GO sheets on rigid and flexible hydrophobic substrates, the amphiphilic copolymer poly(Oligo Ethylene Glycol methyl ether Methacrylate [OEGMA]- Glycidyl Methacrylate [GMA]- Lauryl Methacrylate [LMA]) with additional hydrophobic block was used. The results show that the obtained GO layers had well-defined and uniform structure. Thus, it leads to enhanced hydrophobic-hydrophobic (van der Waals) interaction between the hydrophobic substrate and GO. To this end, the morphology, opto-electrical properties and electro-mechanical stability of chemically reduced GO layers are also investigated. Finally, we demonstrate the excellent stability of rGO on polymeric substrates with no delamination or significant loss in conductivity even after 50000 bending cycle.

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