R. Ashkar, C. Bertrand, M. Abdulbaki, M. Tyagi, A. Faranone, P. Butler, R. Krishnamoorti
National Institute of Standard and Technology, United States
pp. 444 - 447
Keywords: polymer dynamics, local mobility, structural relaxations, percolation, kinetic arrest
Carbon nanocomposites have received significant attention owing to the unique properties of carbon nanoparticles. However, the promised enhancement in carbon nanocomposites has not been fulfilled yet. Lately, there has been a growing consensus that material properties – such as plasticity, fragility, and physical ageing – are intimately linked to the interfacial polymer properties and the hierarchy of polymer dynamics within the nanocomposite. The bottleneck in this direction is the spatial and temporal limitations of conventional probes in accessing these interfacial properties. In this study, we use neutron spectroscopy as a unique direct probe of polymer dynamics in PMMA composites with single-wall-nanotubes (SWNT) and fullerenes (C60). By combining neutron backscattering and neutron spin echo spectroscopy, we access polymer dynamics from local atomic displacements to mesoscale structural relaxations. The measurements reveal a picture of transiently pinned interfacial polymer segments in both types of composites. Due to chain connectivity, this suppression of local polymer mobility at the inetrfaces induces dynamically-slow interfacial polymer regions which, can have a nontrivial effect on non-interfacial dynamics. For particle loadings above the percolation threshold, the percolated nanoparticle network, be it SWNT or C60, forms a kinetic cage that arrests both local and cooperative relaxations of non-interfacial polymer segments.