Dynamic Crossovers and Stepwise Solidification of Confined Water: A (2)H NMR Study.
(2)H NMR reveals two dynamic crossovers of supercooled water in nanoscopic (∼2 nm) confinement. At ∼225 K, a dynamic crossover of liquid water is accompanied by formation of a fraction of solid water. Therefore, we do not attribute the effect to a liquid-liquid phase transition but rather to a change from bulk-like to interface-dominated dynamics. Moreover, we argue that the α process and β process are observed in experiments above and below this temperature, respectively. Upon cooling through a dynamic crossover at ∼175 K, the dynamics of the liquid fraction becomes anisotropic and localized, implying solidification of the corresponding water network, most probably, during a confinement-affected glass transition.
Institut für Festkörperphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany.
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M
Sattig
Institut für Festkörperphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany.
M
M
Vogel
glass transition; liquid−liquid transition; mesoporous silica; spin-lattice relaxation; stimulated echo experiments; supercooled liquid