Results by differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS) are presented in this work, monitoring the interplay between confined, interfacial, and bulk polymer dynamics in silica–gel/polydimethylsiloxane (PDMS) systems. Confined and bulk mobility could be distinguished by recording two well separated glass transition steps in DSC. For low content of adsorbed PDMS (40 wt%), two contributions to segmental dynamics were detected by BDS, arising from the polymer in the interfacial layer on the surfaces of nanoparticles (αint relaxation) and from polymer chains confined in the pores (∼6–20 nm in diameter) of silica–gel (αp), while no bulk segmental relaxation was detected. Nanozirconia grafted onto inner and external surfaces of silica–gel resulted, on the one hand, in reduction of the number of polymer–filler contact points and, on the other hand, in more severe spatial confinement of the polymer in pores. Two additional processes contribute to the dielectric response for the higher polymer loading (80 wt%), arising from the bulk–unaffected amorphous polymer chains (α relaxation) and the constrained polymer mobility between condensed crystal regions (αc). Thermal annealing suppressed the interfacial and bulk (via crystallization) polymer mobility, whereas the confined polymer dynamics remained completely unaffected. The interfacial characteristics could be described well in terms of bimodal conformations of polymer chains, similarly to polymers adsorbed on flat solid surfaces, and in terms of changes in apparent interfacial layer thickness.
Polymer – Elsevier
Published: Feb 10, 2016
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