Unique structure and dynamics of poly(ethylene oxide) in layered silicate nanocomposites: Accelerated segmental mobility revealed by simulating ESR spectra of spin-labels, XRD, FTIR, and DSC

The structure and dynamics of poly(ethylene oxide) (PEO) intercalated in the galleries of a fluoromica inorganic clay were studied by spin-label electron spin resonance (ESR), XRD, FTIR, and DSC. The polymer was end-labeled by attachment of a nitroxide radical. Basic structural information was determined by XRD, while DSC and FTIR revealed that the crystallization of the PEO was inhibited in the clay galleries. The temperature variation of the ESR spectra from the spin-label was simulated based on the "macroscopic order with microscopic disorder" (MOMD) model. For PEO intercalated in the narrow (0.33 nm) clay galleries, the ESR spectra indicated a very low segmental mobility even at high temperature, 410 K, which was attributed to the strong polymer interaction with the charged mica platelets. In wider (0.83 nm) galleries, however, the parameters used to simulate the ESR spectra of the nitroxide labels reflected a lowering,of the PEO segmental density: In this sample, the ESR spectrum consisted of two distinct contributions from slow- and fast-motional components, and the relative intensity of the fast component increased with an increase in temperature. The two spectral components were attributed to segments located close to, and away from, the polar solid walls in the gallery, respectively. Interestingly, the fast-motional component had higher mobility compared to that of PEO chains adsorbed on the fluoromica surface. In addition, the activation energy of the segmental motion in the fast-motional component was lower compared to that of bulk PEO. The low segmental density and reduced cooperative motion with neighboring segments are considered the main factors leading to the fast PEO chain motion with low activation energy.