Dynamics of Adsorbed Polymer Chains in Polymer Nanocomposite Melts

The dynamics of polymer chains and chain segments near an enthalpically attractive interface can be significantly perturbed from the bulk state and can dictate properties in polymer nanocomposites (PNCs). In this work, we directly observe and quantify polymer chain-scale desorption from nanoparticles in the melt using elastic recoil detection and Rutherford backscattering spectrometry on model PNCs comprised of poly(2-vinyl pyridine) and 25-nm diameter silica nanoparticles. We observe polymer desorption ~10³ times slower than bulk chain diffusion and desorption that is slowest for longer chains and at lower temperatures. In this highly attractive system, we observe bound polymer that persists after more than 10⁶ reptation times, even at T_g+100°C. By correlating the measured bound polymer to the nanoparticle concentration, we measure the adsorbed chain areal density as ~0.05 chains per nm² and extract a bound layer thickness that extends ~R_g from the nanoparticle surface, two parameters that have been difficult to experimentally probe in the melt state.