The role of interfacial interactions in the dynamic mechanical response of functionalized SWNT-PS nanocomposites

The dynamic mechanical properties of nanocomposites of functionalized single-walled carbon nanotubes dispersed in polystyrene are reported as a function of temperature. For nanocomposites containing less than 0.1 wt% nanotubes, the enhancement of the magnitude of the complex modulus |E∗|=E′2+E″2, where E′ and E″ are the elastic and loss moduli, respectively, exceeded the predictions of the Halpin-Tsai model (this model is often used to predict the properties of macroscopic composites). In this concentration range, however, the loss tangent, tan δ = E″/E′, of the nanocomposite remained comparable to that of pure PS, i.e., comparable elasticity. At larger concentrations the mechanical response became more elastic than PS, but the magnitude of the complex modulus fell appreciably below predictions based on the Halpin-Tsai model. An alternate hypothesis that relies on the role of attractive interactions between the nanotubes and polystyrene chains, and consistent with previous Raman scattering and glass transition temperature data, is proposed to describe the observed dynamic response.