Dynamics of novel nanocomposites: Solid state NMR study with noise spectroscopy

The dynamics and the microscopic structures of nano-composite materials intercalated with polymers were investigated by solid state NMR. Noise spectroscopy was applied to obtain true wideband absorption spectra in the solid state using a new extended noise excitation method in the linear response limit. This new excitation scheme is based on the realization that there is no obvious requirement for the now- traditional synchronization of pulse repetition rate ($Dt$) and data acquisition rates (τ_samp). Spectral bandwidths in excess of 500 kHz are achieved without substantial modifications to either probe or spectrometer, and deuterium powder pattern lineshapes which span 250 kHz are demonstrated to be faithfully reproduced, using rf fields as weak as a few hundred Hz even in the presence of intermediate dynamics.; This technique is also applied to a nanocomposite polymer electrolyte created when poly(ethylene oxide) is intercalated into a layered silicate, Li-montmorillonite. We were able to characterize both the Li+-silicate distance and the cation dynamics by analysis of the changes in 7Li nuclear magnetic resonance (NMR) lineshape observed as the temperature is changed and cation diffusion is enabled, where the true absorption spectra were essential for analysis. Simulation of 7Li spectra and comparison to experimental data shows that Li+ interacts most strongly with the silicate surface layer and the cation diffusion is restricted to the surface. Lineshape narrowing is observed over the temperature range 270 ≤ T ≤ 400 K, reflecting diffusion along the silicate surface. At higher temperatures motional narrowing leads to a limiting linewidth which depends on the spacing between silicate planes and not on the spacing between Li+ and those planes. Li+ diffusion rates appear consistent with values reported previously for this system and with a simplified lineshape analysis.; In addition, solid state NMR techniques are applied to probe the structure and dynamics of the nanocomposite created when poly(styrene) is intercalated into a surface-modified fluorohectorite. A comparison between surface-sensitive cross polarization experiments with spin-echo experiments suggest that PS acts as if highly plasticized in the center of the nanopores, while chain parts which interact strongly with the surface seem dynamically inhibited.