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DY: Fachverband Dynamik und Statistische Physik

DY 13: Glasses and Glass Transition (joint session DY/CPP)

DY 13.7: Vortrag

Montag, 16. März 2020, 17:00–17:15, ZEU 118

Dynamics of Ethylene Glycol Water Mixtures in Bulk and Mesoporous Silica Studied by Nuclear Magnetic Resonance and Dielectric Spectroscopy — •Philipp Monnard, Melanie Reuhl, and Michael Vogel — TU Darmstadt, Institut für Physik kondensierter Materie, Hochschulstr. 6, 64289, Darmstadt, Germany

Hydrogen bonds remain a topic of scientific interested because of their key role in countless chemical systems. Aqueous solutions of ethylene glycol (EG) create complex networks of hydrogen bonds, because of EGs ability to form both intramolecular and intermolecular bonds. Those solutions are also widely used in heating, cooling and deicing applications, since their freezing point is significantly lower than that of their components. Using nuclear magnetic resonance (NMR) and dielectric spectroscopy (DS), we analyze the effect of silica confinement on the dynamics of EG-water mixtures with different concentrations. In particular, we determine the dependence of correlation times on the pore diameter over a broad temperature range. In doing so, we exploit the isotope selectivity of NMR to observe only the partially deuterated EG-d4(C2D4(OH)2) molecules. Further, we prepared solutions, with heavy water and EG-d2(C2H4(OD)2) to measure the dynamics of the counterpart. We found that the dynamics depend on the mixing ratio, explicitly there is a slowdown with higher concentrations of EG. Moreover, we observe strong dynamical heterogeneity and, for solutions of 30 wt.% EG, the relaxation is even bimodal at intermediate temperatures.