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NMR studies on the temperature-dependent dynamics of confined water

Sattig, Matthias and Reutter, Stefan and Fujara, Franz and Werner, Mayke and Buntkowsky, Gerd and Vogel, Michael (2014):
NMR studies on the temperature-dependent dynamics of confined water.
In: Physical Chemistry Chemical Physics, pp. 19229-19240, 16, (36), ISSN 1463-9076, [Online-Edition: http://dx.doi.org/10.1039/C4CP02057J],
[Article]

Abstract

We use H-2 NMR to study the rotational motion of supercooled water in silica pores of various diameters, specifically, in the MCM-41 materials C10, C12, and C14. Combination of spin lattice relaxation, line-shape, and stimulated-echo analyses allows us to determine correlation times in very broad time and temperature ranges. For the studied pore diameters, 2.1-2.9 nm, we find two crossovers in the temperature-dependent correlation times of liquid water upon cooling. At 220-230 K, a first kink in the temperature dependence is accompanied by a solidification of a fraction of the confined water, implying that the observed crossover is due to a change from bulk-like to interface-dominated water dynamics, rather than to a liquid liquid phase transition. Moreover, the results provide evidence that a process-like dynamics is probed above the crossover temperature, whereas beta process-like dynamics is observed below. At 180-190 K, we find a second change of the temperature dependence, which resembles that reported for the beta process of supercooled liquids during the glass transition, suggesting a value of T-g approximate to 185 K for interface-affected liquid water. In the high-temperature range, T > 225 K, the temperature dependence of water reorientation is weaker in the smaller C10 pores than in the larger C12 and C14 pores, where it is more bulk-like, indicating a significant effect of the silica confinement on the a process of water in the former 2.1 nm confinement. By contrast, the temperature dependence of water reorientation is largely independent of the confinement size and described by an Arrhenius law with an activation energy of E-a approximate to 0.5 eV in the low-temperature range, T < 180 K, revealing that the confinement size plays a minor role for the beta process of water.

Item Type: Article
Erschienen: 2014
Creators: Sattig, Matthias and Reutter, Stefan and Fujara, Franz and Werner, Mayke and Buntkowsky, Gerd and Vogel, Michael
Title: NMR studies on the temperature-dependent dynamics of confined water
Language: German
Abstract:

We use H-2 NMR to study the rotational motion of supercooled water in silica pores of various diameters, specifically, in the MCM-41 materials C10, C12, and C14. Combination of spin lattice relaxation, line-shape, and stimulated-echo analyses allows us to determine correlation times in very broad time and temperature ranges. For the studied pore diameters, 2.1-2.9 nm, we find two crossovers in the temperature-dependent correlation times of liquid water upon cooling. At 220-230 K, a first kink in the temperature dependence is accompanied by a solidification of a fraction of the confined water, implying that the observed crossover is due to a change from bulk-like to interface-dominated water dynamics, rather than to a liquid liquid phase transition. Moreover, the results provide evidence that a process-like dynamics is probed above the crossover temperature, whereas beta process-like dynamics is observed below. At 180-190 K, we find a second change of the temperature dependence, which resembles that reported for the beta process of supercooled liquids during the glass transition, suggesting a value of T-g approximate to 185 K for interface-affected liquid water. In the high-temperature range, T > 225 K, the temperature dependence of water reorientation is weaker in the smaller C10 pores than in the larger C12 and C14 pores, where it is more bulk-like, indicating a significant effect of the silica confinement on the a process of water in the former 2.1 nm confinement. By contrast, the temperature dependence of water reorientation is largely independent of the confinement size and described by an Arrhenius law with an activation energy of E-a approximate to 0.5 eV in the low-temperature range, T < 180 K, revealing that the confinement size plays a minor role for the beta process of water.

Journal or Publication Title: Physical Chemistry Chemical Physics
Volume: 16
Number: 36
Uncontrolled Keywords: nuclear-magnetic-resonance spin-lattice-relaxation organic glass formers mesoporous silica materials slow beta-process solid-state nmr neutron-scattering deuteron nmr mcm-41 transition
Divisions: 05 Department of Physics
05 Department of Physics > Institute for condensed matter physics
07 Department of Chemistry
07 Department of Chemistry > Physical Chemistry
Date Deposited: 27 Oct 2014 20:49
Official URL: http://dx.doi.org/10.1039/C4CP02057J
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Ao4ia Times Cited:0 Cited References Count:64

Identification Number: doi:10.1039/C4CP02057J
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