Peculiar polymer dynamics in PMMA/SWNT composites

Rana Ashkar, Ramanan Krishnamoorti, Paul Butler, Madhusudan Tyagi, Antonio Faranone and Mansour Abdulbaki
National Institute of Standard and Technology, US

Keywords: nanocomposites, SWNT, segmental dynamics, polymer caging

Summary:

Single-wall carbon nanotube (SWNT) composites have been repeatedly shown to exhibit advanced properties relative to the host polymer, owing to the superior performance of the carbon nanotubes and their interaction with the surrounding polymer chains. We find that the addition of the nanotubes influences not only the material performance but also the dynamics of the polymer matrix. In this work, we report on polymer dynamics on PMMA composites with percolated SWNT networks obtained with different filler loadings (1, 8 and 15 v%). Neutron spin echo (NSE) is implemented for the investigation of chain relaxations and backscattering (BS) spectroscopy for tracking molecular motions. Backscattering measurements show that the polymer mobility is increasingly suppressed with increasing SWNT loading but the mean square displacements are almost independent of the SWNT concentration. This suggests that the percolation of the nanotubes induces connectedness in the dynamically slow domains of the nearby polymer chains, which in turn impose dynamical constraints on the otherwise fast bulk domains. Supporting NSE data on the composites show an order of magnitude slowdown in the chain relaxations relative to pure PMMA, which further corroborates the dynamic caging hypothesis.