Carbon nanotube/epoxy nanocomposites: Effect of interfacial chemistry and processing on molecular mobility, cure behavior, morphology and properties

The potential to enhance the mechanical and electrical properties of polymers by incorporating carbon nanotubes has generated significant interest in industry and academia. Over the last 10 years, considerable academic research has been devoted to synthesis and characterization of these nanocomposite materials, and much is now known about their unique properties. However, before these nanocomposites can reach their full technological potential, the precise mechanism(s) by which carbon nanotubes enhance properties of polymers must be fully understood. The goal of this research was to study the process-structure-property relationships of surface functionalized carbon nanotube/polymer nanocomposites. Carboxylated and fluorinated nanotubes were used to synthesize nanocomposites by dispersing them separately in an epoxy resin using a high shear mechanical method to align the nanotubes. Dynamic mechanical analysis, using torsional deformation, was applied both parallel and perpendicular to the long axis of the multiwall nanotubes. Interestingly, for epoxy/MWNT (1 wt%) nanocomposites, the shear moduli in the glassy state were higher for the nanocomposites, and its highest for the nanocomposites in which the nanotubes are parallel to the direction of applied torque. These nanocomposites also exhibited higher Tgs than the neat resin.;The effect of alignment on the processing-structure-property relationships has been studied using magnetically aligned MWCNT/epoxy nanocomposites. The sample was prepared by dispersing the nanotube in the epoxy and curing under an applied magnetic field. The modulus parallel to the alignment direction, as measured by dynamic mechanical analysis, showed significant anisotropy, with a 72% increase over the neat resin, and a 24% increase over the sample tested perpendicular to the alignment direction.;The effect of nanotube modification on the curing the epoxy resin was also studied using differential scanning calorimetry, rheology and infrared spectroscopy. Activation energy and rate constants obtained from isothermal DSC were the same for the neat resin and fluorinated MWCNT system whereas samples containing carboxylated MWCNTs exhibited a higher activation energy and lower rate constant. Comparison of the activation energies, rate constants, gelation behavior and vitrification times for all of the samples suggest that the cure mechanisms of the neat resin and fluorinated sample are similar but different from the carboxylated sample.