Chemical Fragmentation and Properties of Bulk Graphite and Inorganic Graphite Analogs Produced for Large-Scale Applications in Polymer Composites

The inherent nature of nanomaterials is not well understood, and production of polymer nanocomposites suitable for commercialization is still in its infancy. Polymer nanocomposites have displayed enhanced mechanical, thermal, electrical, and lubricating properties, which are dependent upon nanomaterial characteristics and dispersion. Chemical functionalization of nanomaterials to increase dispersion in various polymer matrices has been shown to further enhance properties. However specific understanding of the chemical and structural properties of modified nanomaterials and commercial scalability is rarely addressed. In this dissertation, we present the chemical fragmentation of 3-D layered hexagonal powders to generate large quantities of exfoliated and edge functionalized materials for dispersion in various polymer matrices.

Commercial precursor powders of 3-D hexagonal layered graphite, multi-layered graphene, molybdenum sulfide, and boron nitride were liquid-exfoliated using ultrasonication under various conditions to prepare large quantities of exfoliated materials. This dissertation focuses on the chemical exfoliation of these materials and the subsequent detailed chemical and structural material characterization. Furthermore understanding of the role of edge oxidation during the exfoliation process was studied, and the effects on the macroscopic properties were determined. Characteristic conductivities of graphite and graphene were greatly decreased, implying chemical and/or physical quenching of electrons. Solution characteristics were studied and solution blending with polymers was performed to produce composites. Thermal characterization of the composites demonstrated poor interaction between filler and nonpolar polymers like polystyrene (PS) and poly(cyclohexadiene) (PCHD).

Considering the significance of solution characteristics for determining suitable polymer matrices and the effects on properties, a major part of this dissertation focuses on the colloidal behavior of the fragmented materials. Furthermore given the dispersion characteristics of the restacked materials, solution blending was used to generate composites, and the resulting effects on the macroscopic properties are reported. The addition of sodium bisulfite (SBS) during fragmentation of molybdenum disulfide (MoS₂) sheets appeared to generate a multiphase material, possibly from ion intercalation. The photoluminescence and lubricity of fragmented MoS₂ particles in aqueous dispersions and poly(ethylene glycol) (PEG) solutions suggested a means to produce tailored particles, desirable for applications in coatings or slurries.