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Intermixing between chemically different polymers around nanoparticles creates chemically heterogeneous layers, exhibiting unusual dynamic anomalies due to dynamic confinement and coupling phenomena in polymer nanocomposites. Interfacial mixing of chains is possible when adsorbed chains are mobile above their glass-transition temperature, leading to enhanced entanglement density at the interphase. Linear rheology data of polymer nanocomposites with chemically heterogeneous interphases around nanoparticles were analyzed over a wide frequency range to investigate the role of chain rigidity on matrix chain relaxations and particle diffusion. Our findings show that nanoparticles adsorbed with less rigid polymer move in a sub-diffusive mode. Nanoparticles adsorbed by flexible polymers can slow down the matrix polymer dynamics and particle diffusion, and this interphase effect enhances the viscoelastic properties of the whole polymer nanocomposite. [ABSTRACT FROM AUTHOR]

We investigated the dynamics of nanocomposites prepared through mixing poly(methyl methacrylate) grafted Fe 3 O 4 nanoparticles (PMMA- g -Fe 3 O 4 ) with poly(methyl acrylate) (PMA). A key feature here different from previous dynamics measurements of polymer nanocomposites is the different chemistry between the matrix polymer and the polymer grafts, which introduces chemical heterogeneity. Transmission electron microscopy shows clear evidence of nanoparticle clustering due to the poor miscibility between the bulk PMA and the bulk PMMA. At the same time, broadband dielectric spectroscopy measurements detect two leading relaxations, i.e. the α and α * processes, where the α process is associated with the bulk PMA and the α * process from the PMA interacting with the grafted PMMA in the nanoparticle clustering region. Interestingly, the characteristic time of α *, τ α * , is slightly slower than that of the α , τ α , at high temperatures, and exhibits near Arrhenius temperature dependence at low temperatures. As a result, τ α * and τ α cross each other in the activation plot upon cooling and τ α * ≪ τ α is observed at temperatures approaching the glass transition temperature of PMA. These observations suggest the presence of component dynamics and the dynamics confinement effect between PMA and PMMA in the nanoparticle clustering region, highlighting an active interaction between PMA and PMMA at the interface despite their poor miscibility. These results thus suggest new routes to control interface dynamics through immiscible polymer pairs.