Micromechanics modeling of the multifunctional nature of carbon nanotube-polymer nanocomposites

The present work provides a micromechanics approach based on the generalized self-consistent composite cylinders method as a non-Eshelby approach towards for assessing the impact of carbon nanotubes on the multi-functional nature of nanocomposites in which they are a constituent. Emphasis is placed on the effective elastic properties as well as electrical and thermal conductivities of nanocomposites consisting of randomly oriented single walled carbon nanotubes in epoxy. The effective elastic properties of aligned, as well as clustered and well-dispersed nanotubes in epoxy are discussed in the context of nanotube bundles using both the generalized self-consistent composite cylinders method as well as using computational micromechanics techniques. In addition, interphase regions are introduced into the composite cylinders assemblages to account for the varying degrees of load transfer between nanotubes and the epoxy as a result of functionalization or lack thereof. Model predictions for randomly oriented nanotubes both with and without interphase regions are compared to measured data from the literature with emphasis placed on assessing the bounds of the effective nanocomposite properties based on the uncertainty in the model input parameters.; The generalized self-consistent composite cylinders model is also applied to model the electrical and thermal conductivity of carbon nanotube-epoxy nanocomposites. Recent experimental observations of the electrical conductivity of carbon nanotube polymer composites have identified extremely low percolation limits as well as a perceived double percolation behavior. Explanations for the extremely low percolation limit for the electrical conductivity of these nanocomposites have included both the creation of conductive networks of nanotubes within the matrix and quantum effects such as electron hopping or tunneling. Measurements of the thermal conductivity have also shown a strong dependence on nanoscale effects. However, in contrast, these nanoscale effects strongly limit the ability of the nanotubes to increase the thermal conductivity of the nanocomposite due to the formation of an interfacial thermal resistance layer between the nanotubes and the surrounding polymer. As such, emphasis is placed here on the incorporation of nanoscale effects, such as electron hopping and interfacial thermal resistance, into the generalized self-consistent composite cylinder micromechanics model.