Interface effects on the viscoelastic characteristics of carbon nanotube polymer matrix composites

Abstract

It is generally known that load transfer from the polymer matrix to carbon nanotubes (CNTs) can be greatly hindered due to the pristine CNT surface condition. This imperfect condition can have a profound influence on the effectiveness of CNT reinforcement. In order to address this issue in the context of viscoelastic response, an effective medium theory is first presented, and then applied to study the effect of interfacial sliding on the time-dependent creep, stress relaxation, strain-rate sensitivity, and storage and loss moduli of a multi-walled CNT/polypropylene nanocomposite. We show that, without accounting for the imperfect load transfer at the interface, the predicted creep compliances are too stiff, but with the introduction of a weakened interface, the measured creep curves at various CNT loading can be well captured. Both stress relaxation and stress–strain relations are also found to greatly depend on the interface condition. Under low-frequency harmonic loading our calculations also reveal that the interface condition is further weakened and that a larger interface sliding parameter is required to reflect the measured storage and tangent moduli. We conclude that the viscoelastic characteristics of a CNT nanocomposite are very sensitive to the interface condition, and that continued improvement in surface functionalization is necessary to realize the full potential of CNT reinforcement.