Carbon nanotube networks in epoxy composites and aerogels

This thesis describes the properties of carbon nanotube networks in epoxy composites and in novel carbon nanotube aerogels.;SWNT Epoxy composites were created using a new procedure that enabled us to control SWNT concentration and dispersion quality in the composite. The composites exhibited percolation-like electrical conductivity with threshold volume fractions in the semi-dilute nanotube concentration regime. The observed electrical conductivites are described in terms of nanotube length, degree of aggregation, and sample homogeneity. By modifying the procedure to allow for nanotube chaining, conductive composites were created at SWNT volume fractions as low as 5.2 (+1.9/-0.5) x 10-5, the lowest reported to date. The thermal conductivity of SWNT-epoxy composites is also investigated. Composites were prepared using suspensions of SWNTs in N-N-Dimethylformamide (DMF) or surfactant stabilized aqueous SWNT suspensions. Thermal conductivity enhancement was observed in both types of composites, but DMF-processed composites showed an advantage at SWNT volume fractions between &phis; ∼ 0.001 to 0.005. Surfactant processed samples, however, allowed greater SWNT loading at which a larger overall enhancement (64 +/- 9) % at &phis; ∼ 0.1 was observed. The enhancement differences are attributed to a tenfold higher SWNT/solid-composite interfacial thermal resistance in the surfactant-processed composites over DMF-processed composites. The interfacial resistance was extracted from the data using effective medium theory.;Carbon nanotube aerogels were created by freeze drying and critical point drying aqueous carbon nanotube gels. The resulting aerogels have densities of approximately 0.01 to 0.06 g/cm3 and maintain the dimensions of the wet gel. Critical point dried aerogels also preserve the microscopic three-dimensional network of debundled carbon nanotubes of the original gel. Pure SWNT aerogels are self-supporting. Reinforcement with small amounts of added polyvinyl alcohol (PVA) produces much stronger structures that can support at least 8000 times their own weight. Electrical conductivity of order 1 S/cm is observed in the self-supporting aerogels, and at least 10-2 S/cm can be achieved in PVA-reinforced aerogels through additional processing. The aerogels have potential applications in areas such as sensors, novel battery or supercapacitor electrodes, and ultra-light structural materials. They can be backfilled with polymers or other materials to create composites that retain the high conductivity of the network.