| The objectives of this work were to functionalize two nanoparticles, layered silicate clay and expanded graphite, and evaluate the effects of surface modification on polymer nanocomposite properties. Two thermosetting resin systems were evaluated, a polyimide for high temperature applications, and a general use epoxy. The chemistry of the modifier or the particle surface was tailored in each case to optimize nanocomposite properties such as: particle dispersion, thermal oxidative stability (TOS), electrical conductivity, strength, and toughness.;Dispersion of layered silicate clay into the two separate matrices demonstrated an apparent affinity between the silicate surface and aromatic compounds. Steps were taken in each case to disrupt that attraction; resulting in improved material properties. The dispersion of layered silicate clays into a thermosetting polyimide demonstrated that improved thermal oxidative stability was achieved only when the clay was modified with a combination of an aromatic diamine and an alkyl ammonium ion. When such a system was employed, the nanocomposite TOS improved by 25% over that of the base polyimide. Attention to the interactions between clay and aromatic containing compounds was also necessary for silicate modification and dispersion in an epoxy blend. Here, preferential contact between the clay and the aromatic containing sections of the blend was observed; resulting in nanocomposites exhibiting little enhancement to epoxy properties. By forcing the clay into the non-aromatic component, the material yield stress increased by up to 65%, Young's modulus increased by up to 80%, and increases in Tg of up to 11°C were observed relative to the base resin.;Within nano-graphite containing materials, trade-offs in functionalization, dispersion, and properties were evaluated. Functionalization of graphite proved beneficial in terms of dispersion. For example, an epoxy functionalized graphite nanoparticle resulted in acceptable dispersion throughout the matrix, with a minimal level disruption of the sp2 hybridization within the graphene sheet. As a result, the nanocomposite structure increased yield stress by 30% at a filler loading of 0.67 vol%. Electrical conductivity increased by 5 orders of magnitude at this same loading. Graphite materials that did not disperse well, or were more heavily oxidized exhibited conductivity as loading increased to 1.5 vol%. In the poorly dispersed expanded graphite material, a 35% increase in yield stress was observed, but with significant reduction in ductility. With the heavily oxidized graphene sheets, 50% increase in yield stress was observed, following adjustments to the resin stoichometry. |
