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Segmental Diffusion in Attractive Polymer Nanocomposites: A Quasi-Elastic Neutron Scattering Study

Bailey, Eric J., Griffin, Philip J., Tyagi, Madhusudan, Winey, Karen I.
Macromolecules 2019 v.52 no.2 pp. 669-678
diffusivity, glass transition, models, molecular weight, nanoparticles, neutron diffraction, polymer nanocomposites, silica, temperature
We present a systematic study of segmental dynamics in model attractive polymer nanocomposites comprising poly(2-vinylpyridine) (P2VP) and 26 nm diameter colloidal silica nanoparticles (NPs) using quasi-elastic neutron scattering (QENS). Unlike most dynamic measurements, QENS provides both spatial and temporal information about small length scales (∼1 nm) and fast time scales (∼1 ns) and therefore at temperatures far above the glass transition. We find that on these length and time scales P2VP segmental motion is well-described by classic translational diffusion even under extreme confinement, where the average interparticle spacing is on the order of the Kuhn length. The average segmental diffusion coefficient decreases monotonically with increasing NP concentration by up to a factor of ∼5 at the highest NP concentrations (50 vol %). Interestingly, this reduction in segmental dynamics is very weakly dependent on P2VP molecular weight spanning the unentangled (10 kg/mol) to the highly entangled regimes (190 kg/mol). This stands in contrast to the well-documented molecular weight effect on segmental dynamics in attractive polymer nanocomposites at lower temperatures.