Dresden 2009 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 15: POSTERS Dynamics and Diffusion
CPP 15.5: Poster
Tuesday, March 24, 2009, 14:00–16:30, P3
Water dynamics on the hydrate lattice of a tetra-butyl ammonium bromide semi-clathrate — •Sebastian Schildmann, Andre Nowaczyk, Burkhard Geil, Catalin Gainaru, and Roland Böhmer — Experimentelle Physik III, Fakultät für Physik, Technische Universität Dortmund
Deuteron nuclear magnetic resonance (NMR) and dielectric spectroscopy are utilized to investigate the dynamics of the water molecules in the tetra-n-butyl ammonium bromide semi-clathrate (TBAB · 26H2O). Semi-clathrates are nano-porous structures suitable for the encapsulation of small guest molecules which here are part of the water lattice. Stimulated-echo spectroscopy and dielectric measurements were employed and yielded the same distribution of correlation times corresponding to a mean activation energy of about 5165 K. Solid-echo spectra were acquired over a broad temperature range and compared with random-walk simulations. They exhibit an apparent two-phase character which is discussed in terms of various scenarios. Two-dimensional NMR spectra and four-time stimulated echoes were recorded, but an exchange between slow and fast reorienting molecules could not be detected. Spin-lattice relaxation does not directly reflect the local reorientational motion and its non-exponentiality is interpreted with reference to the translational dynamics of the water molecules. Estimated diffusion coefficients suggest that a translational step takes place after every 10th reorientational step. Replacing the bromide anion by fluoride the semi-clathrate TBAF · 32H2O is investigated and compared with the former results.