In polymer nanocomposites, the ability of a filler to enhance the mechanical and thermal transport properties of a matrix relies on the effectiveness of the matrix-filler transfer of mechanical load and thermal energy, respectively. These transfer effects, in turn, depend on the thermo-mechanical behavior of the matrix-filler interphase region in the nanocomposite. We use atomistically detailed simulations to probe the effect of the functionalization of carbon nanotubes (CNTs) on the properties of the interphase region in cross-linked epoxy nanocomposites, which remain poorly understood. Previously, we had found that the weak interfacial interactions between the cross-linked epoxy and the pristine CNTs not only cause a large depression in the glass transition temperature (Tg) of the nanocomposite compared to the neat polymer, but also lead to an enhancement in the compressibility of the interphase region compared to the bulk matrix. Calculation of the Young's modulus of these systems shows that this enhanced compressibility of the interphase reduces the ability of the pristine CNTs to increase the stiffness of the matrix. On the other hand, functionalization of the CNTs leads to the creation of covalent bonds between the CNTs and the matrix, and pins the CNTs to the matrix. This aspect leads to the creation of a less compressible interphase region. As a result, the Young's modulus of the nanocomposite containing functionalized CNTs is ~50% higher than that of the neat polymer. Along similar lines, calculations of the thermal conductivity show that the use of functionalized CNTs in the nanocomposite leads to ~21% increase in the thermal conductivity of this nanocomposite compared to that of the nanocomposite containing pristine CNTs. Our simulation results suggest a molecular mechanism for the crazing phenomenon that has been reported in literature based on experimental work on nanocomposites containing functionalized CNTs.

Role of the interphase in the transfer of mechanical load and thermal energy between the matrix and the filler in cross-linked epoxy: Carbon nanotube nanocomposites

247th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.