USING NONCOVALENT BONDING TO IMPROVE THE INTERFACE BETWEEN GRAPHENE NANOPLATELETS AND AN EPOXY MATRIX

Epoxy polymers offer superior chemical and thermal resistance, mechanical properties, and are easily processable compared to similar performing materials. Graphene nanoplatelets (GnP) added as a nanofiller to a polymer create polymer nanocomposites with multifunctional properties. GnP, few-layer stacks of atomically thin graphene sheets with diameters in the micron range, have excellent mechanical, thermal, and electrical properties. Composite performance depends on the ability of the polymer to interact strongly with the GnP. Due to the platelet morphology and the chemically inert GnP basal plane surface, interactions with the epoxy resin are limited to a few edge sites and weak van der Waals intermolecular interactions with the basal plane. This dissertation investigates improving the noncovalent interfacial interactions between GnP and an epoxy resin through the use of a bi-functional interfacial molecule that can interact simultaneously with the GnP and epoxy polymer. An interfacial molecule was synthesized to form strong noncovalent interactions with the GnP surface and covalent bonding with the epoxy resin utilizing a condensation reaction between 1-pyrenealdehyde and poly(oxypropylene) diamine. GnP-epoxy nanocomposites were produced using an epoxy/amine polymer matrix. Several model interfacial molecules were used to investigate the effects on the composite properties. A poly(oxypropylene) diamine was adsorbed onto the GnP surface and reacted with the epoxy in the curing process. The resulting composite exhibited reduced flexural modulus and glass transition temperature versus the unmodified GnP composites. 1-pyrenealdheyde was investigated as a molecule that could noncovalently attach to the GnP surface through π-π interactions. Due to the intercalative properties of 1-pyrenealdehyde, the GnP was exfoliated and exhibited higher GnP concentration at the same loading volume. As a result, flexural modulus increased by 40%. However, due to a negligible change in interfacial interactions, the flexural strength, glass transition temperature, and loss modulus remained similar to the baseline GnP composites. A third molecule, α-isopropyliminopyrene-ω-amino-poly[oxy(2-methylethylene)] (Py-POP), was synthesized in this research to both noncovalently attach to the GnP basal plane and react into the epoxy matrix. The pyrene end strongly interacts with the GnP surface, and the opposite end of the molecule participates in the epoxy curing mechanism. The length of the polypropylene segment increases the ability of this molecule to connect to the crosslinked epoxy network at a distance away from the GnP basal plane surface. The flexural modulus, flexural strength, and glass transition temperature was improved above the unmodified GnP composites. This signifies improved interfacial interactions between the GnP surface and epoxy matrix. Additionally, significantly increased electrical conductivity represents improved GnP dispersion quality and epoxy adhesion. Stronger interfacial interactions between the GnP surface basal plane and epoxy polymer have shown to improve the composite multifunctionality. The combination of strong noncovalent interactions with the GnP basal plane along with covalent bonding with the epoxy resin using Py-POP resulted in stronger interfacial interactions compared with the poly(oxypropylene) diamine and 1-pyrenealdehyde. Noncovalent bonding an interfacial molecule onto the GnP basal plane improved the nanocomposite multifunctionality while reserving the excellent GnP properties.