Multiscale characterization of polymer dynamics in carbon nanotube grafted fiber-reinforced polymer composites

Grafting carbon nanotubes (CNTs) onto microscale fiber surfaces has improved the mechanical, electrical and thermal properties of fiber-reinforced polymer composites. Using these multifunctional materials for commercial applications involves extensive understanding of their structure-property relationships. The current study attempts to understand the role of CNTs in affecting polymer dynamics and viscoelastic properties as a function of both time (10^-9 s to 10¹⁰ s) and length scale (nm to cm). Dynamic mechanical thermal analysis (DMTA) and elastic neutron scattering (ENS) experiments were conducted on plain epoxy, unidirectional glass fiber reinforced composite (FRP), and unidirectional glass fiber reinforced composite containing 1.35 mass % of multiwall CNTs (CNT-FRP). Master curves generated after time-temperature superposition (TTS) identify minor reinforcements in shear glassy modulus, reductions in the shear rubbery modulus and no major changes in the polymer glass transition temperature (T_g) due to CNT addition. The mean square displacement of the hydrogen atoms measured by ENS indicates that the polymer chain dynamics in the CNT-FRP is enhanced with respect to the FRP specimens near and above T_g.