Interfacial regions and network dynamics in epoxy/POSS nanocomposites unravelling through their effects on the motion of molecular chains

Abstract

Interfacial regions formed by incorporating a certain percentage of nanofillers into a polymer matrix can impact on the motion of molecular groups, chain units or chain segments, and alter molecular chain network dynamics, which is regarded as a key factor to achieve a finer degree control of dielectric properties of polymer nanocomposites. It is of interest to investigate the molecular chain motion behavior at interfacial regions with the incorporation of nanofillers. Epoxy resin/polyhedral oligomeric silsesquioxane (EP/POSS) nanocomposites are fabricated and the observations of morphology structure and chemical elements indicate that POSS nanofillers are well dispersed in the matrix. Differential scanning calorimeter, dynamic thermomechanical analysis, and dielectric relaxation spectroscopy are measured to analyze the effect of nanodoping on the motion properties of molecular chain units and chain segments that satisfy the Arrhenius and Vogel-Fulcher-Tammann equations respectively. The thicknesses of interfacial regions between POSS nanofillers and EP matrix are estimated from dielectric spectra and effective relative permittivity simulations, which are around several nanometers and decrease with the increment in the nanofiller content. In addition, the dielectric spectra scaling analysis indicates that the motion of small chain units can be hindered in interfacial regions and be tuned simultaneously by the variations of molecular chain network structure and dynamics. Nevertheless, the thin interfacial regions cannot effectively restrict the orientation of long molecular chain segments during the glass transition process. The variation of chain segment orientation behavior is ascribed to the interactions among molecular chains tuned by the binding effect of POSS nanofillers.