Effects of Severe Confinement on the Structure and Dynamics in Polymer Nanocomposites

The structure and dynamics of PEO/Na+MMT nanocomposites of various concentrations from pure polymer to pure clay have been investigated by X-Ray diffraction (XRD), Differential Scanning Calorimetry (DSC), and Quasi-elastic Neutron Scattering (QENS). XRD measurements show that at low polymer concentrations, the PEO chains form either a single- or a double-layer structure within the galleries. Further increase of the PEO content reveals only double-layers of intercalated amorphous chains and it is only for PEO content above 70 wt% that diffraction peaks are observed that can be assigned to the crystalline structure of PEO. QENS was utilized to investigate the dynamics of the intercalated PEO chains. The data for the energy-resolved elastic intensity scattered from the samples (elastic scan) show differences in the behavior of PEO in bulk and in confinement. The data for bulk PEO show the existence of dynamics between the glass transition, Tg, and the melting temperature, Tm, as well as an abrupt drop in the intensity at the bulk Tm, whereas the data for the hybrid with 30% PEO are insensitive to the bulk Tm. A jump of the bulk PEO dynamics at Tm is also observed in the quasi-elastic measurements, whereas the dynamics of PEO in confinement shows only a weak temperature dependence that goes smoothly through the bulk Tm, above which it is slower than that in the bulk