Interfacial interactions between the polymer and graphene are pivotal in determining the reinforcement efficiency in the graphene-enhanced polymer nanocomposites. Here, we report on the dynamic process of graphene-induced oriented interfacial crystals of isotactic polypropylene (iPP) in the single fiber polymer composites by means of polarized optical microscopy (POM) and scanning electron microscopy (SEM). The graphene fibers are obtained by chemical reduction of graphene oxide fibers, and the latter is produced from the liquid crystalline dispersion of graphene oxide via a wet coagulation route. The lamellar crystals of iPP grow perpendicular to the fiber axis, forming an oriented transcrystalline (TC) interphase surrounding the graphene fiber. Various factors including the diameter of graphene fibers, crystallization temperature, and time are investigated. The dynamic process of polymer transcrystallization surrounding the graphene fiber is studied in the temperature range 124-132 °C. The Lauritzen-Hoffman theory of heterogeneous nucleation is applied to analyze the transcrystallization process, and the fold surface free energy is determined. Study into microstructures demonstrates a cross-hatched lamellar morphology of the TC interphase and the strong interfacial adhesion between the iPP and graphene. Under appropriate conditions, the β-form transcrystals occur whereas the α-form transcrystals are predominant surrounding the graphene fibers.

We report on a series of experiments on large-area ordered patterns of graphene oxide on solid substrates deposited from aqueous dispersions by directed drop evaporation. The aqueous dispersion of graphene oxide exhibits phase transitions from isotropic to liquid crystalline nematic phases via a biphasic region with increasing concentration. In the single nematic phase, schlieren textures accompanied by oriented bands are frequent. Drying of drops in each phase results in deposition covering the whole drop base. The dynamic process of drop drying is analyzed based on the weight loss, radius change, and texture change over time. It is found that the radial bands develop in the nematic drops in the vicinity of the receding of the contact line and subsequently transform into birefringent stripes after drying. Study into the structure and morphology of the stripes reveals anisotropic wrinkling of graphene oxide sheets. The nature of stripe orientation is strongly dependent on the local nematic order at the dewetting water front. Various macroscopic patterns with different stripe orientations including radial spokes, spider webs, and parallel stripes have been generated by tuning the nematic order of drops.

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Corrosion is a prevalent concern throughout the world, causing significant monetary and safety concerns. Research has been dedicated to developing cost-effective solutions for corrosion that will also meet increasingly stringent environmental regulations. The recently discovered nanomaterial graphene has been proposed as a potential component in anticorrosion technology due to its strong air and water barrier properties. However, graphene is a relatively expensive, difficult to synthesize material. By incorporating it into nanocomposites, its properties can be exploited even at low concentrations. Previous work has been conducted involving the preparation of anticorrosive polystyrene-graphene nanocomposites; these materials were found to be effective long-term barriers for corrosion. Although the polystyrene-graphene nanocomposites were effective in impeding corrosion on metal substrates, their ease of application left some room to be desired. Painting a substrate is currently the most commonly used method for corrosion prevention, but polystyrene is not typically used in paints due to its incompatible properties with these formulations. If somehow anticorrosive nanocomposites could be incorporated into coatings, the ease of application could be greatly improved. Polyurethanes are commonly used as binders for coatings, so the fabrication and characterization of polyurethanegraphene nanocomposites for use in anticorrosive coatings was chosen as the premise for this project. v A number of different physical and chemical nanocomposites were prepared using labsynthesized graphene and graphene oxide, as well as commercial graphene. Both two component waterborne and solventborne polyurethanes were employed, and nanocomposites were prepared by both physical and chemical methods. The nanocomposites were coated on cold-rolled steel panels and subjected to salt spray testing in conjunction with control panels in order to analyze their anticorrosive properties. Nanocomposite films were also characterized to determine how their thermal and mechanical performance compared to control coatings. Despite promising studies that supported the anticorrosive capabilities of graphene, this project found that graphene may not be ready for integration into viable coatings systems. Its complex structure and properties made uniform dispersion throughout polyurethane seemingly unachievable, no matter how many different formulations were attempted. To prepare well-dispersed polyurethane-graphene nanocomposite coatings, new components would definitely be required to prevent aggregation of graphene. These components may already be commercially available, but most likely would have to be developed specifically for these formulations. Without these components, the anticorrosive properties of polyurethane-graphene nanocomposites cannot be accurately studied. vi ACKNOWLEDGMENTS I would like to thank my thesis committee chair for their overwhelming guidance and support throughout my time at Cal Poly. Dr. Raymond Fernando, I never would have discov...