The freezing, melting and dynamics of supercooled water at different hydration of controlled porous glass with mean pore sizes 10 nm, 30 nm, 50 nm and 70 nm are studied using differential scanning calorimetry and deuteruim nuclear magnetic resonance (2H-NMR). For saturated samples, the melting temperature 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 crystallization and melting temperatures as well as enthalpies are lower than for the saturated samples.2H-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 temperature relaxation rate follows the Vogel-Fulcher-Tammann (VFT) relation.
Keywords: Vogel–Fulcher–Tammann equation; freezing–melting; hydration rate; porous glass; supercooled water.
© 2020 IOP Publishing Ltd.