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DF: Fachverband Dielektrische Festkörper

DF 19: Glasses and Glass Transition (CPP with DF)

DF 19.3: Vortrag

Freitag, 24. März 2017, 10:30–10:45, ZEU 118

NMR and BDS Experiments on Water confined in MCM-41 — •Edda Klotz, Matthias Sattig, Christina Lederle, and Michael Vogel — TU Darmstadt Solid State Physics, Darmstadt, Germany

The investigation of the dynamics of water in confinement is relevant for various fields of interest, from biological applications to geological ones. It is well established that confined water undergoes a dynamic crossover upon supercooling. However, the origin of the crossover is controversially discussed. To further study this issue, we focus on water im MCM-41 silica nanopores and use por diameters for which well defined partial freezing occurs. Calorimetric studies are performed to characterize this freezing behavior. Moreover, nuclear magnetic resonance (NMR) and broadband dielectric spectroscopy (BDS) are applied to ascertain the dynamics of the non-freezing water fraction cross the freezing transition. The dielectric spectra exhibit several processes that are sensitive to an appearance of a solid water fraction. ²H-NMR allows us to show that one of the processes can be identified with the rotational motion of water, exhibiting a kink in the temperature depenence at the freezing-transition. Moreover, ¹H static field gradient NMR yields self-diffusion coefficients of water, which can be linked to freezing-affected polarization processes in BDS. Thus, these combined studies clearly show a dynamic crossover due to formation of a solid water fraction.