Freezing, melting and dynamics of supercooled water confined in porous glass

Abstract

The freezing, melting and dynamics of supercooled water at different hydration of controlled porous glass (CPG) with mean pore sizes 10 nm, 30 nm, 50 nm and 70 nm are studied using differential scanning calorimetry (DSC) and deuteruim nuclear magnetic resonance (2 H-NMR). For saturated samples, the melting tempertaure follows the Gibbs-Thomson relation despite a clear linear decrease of the melting enthalpy when the transition is shifted due to confinement. For partially filled porous glasses the crystalization and melting temperatures as well as enthalpy are lower than for the saturated samples. 2 H-NMR confirms the existence of a non-crystallizable part of water adsorbed on the surface of pores. At room temperature, spin-lattice relaxation rate (1/T1) is proportional to the inverse of the mean pore size indicating that the relaxation is governed by a surface limited process. At low tempertaure relaxation rate follows the Vogel-Fulcher-Tammann (VFT) relation.

Metastable disordered phase in flash-frozen Prussian Blue analogues

“…Overall, we find that both the flash-frozen sample and the slowly cooled sample show a transition below 200 K. This transition is within the range of freezing of water confined in the small nanopores (Schreiber et al, 2001;Morishige et al, 2010;Neffati et al, 2020). In the following, we present further evidence from 3D-ÁPDF analysis that water indeed plays an important role in this transition.…”

A gel lattice alters the phase state of a solvent

“…In particular, the melting temperature decreases when a liquid crams into a porous material, and the effect is that it increases with a decrease in the pore size. 24–26 Similar effects were observed in, for example, a water–glass system 27 and even in a non-porous water–protein system. 28 Therefore, if some changes in the properties of the solvent take place in the neighborhood of the TFAAA gel lattice, the properties of such a special phase can be probed with differential scanning calorimetry.…”

Solid State NMR for Nonexperts: An Overview of Simple but General Practical Methods

“…Some other substances have been studies as well [66][67][68][69][70]. Interaction with the surface causes a change in the melting/freezing point of the adsorbate [71][72][73][74][75]. When the confinement is not very tight and the surface concentration is below monolayer coverage, the reorientation of adsorbed molecules is fast on a millisecond time scale and their 1 H NMR linewidths are small [76].…”