The dynamics of water confined in mesoporous MIP (2–3
nm
pores in size) with silica gel (secondary silica; further, the abbreviation
SG will be used) and MAP (10–35 nm pores in size) without SG
borosilicate glasses have been studied by broadband dielectric spectroscopy
(BDS), nuclear magnetic resonance (NMR), and differential scanning
calorimetry (DSC). MIP samples contain secondary silica inside the
pores and provide a confinement size of about 2–3 nm, whereas
MAP samples are free of secondary silica and provide a confinement
size of about 10–35 nm. It is shown by BDS and NMR techniques
that water exhibits a dynamic crossover of around 180 K when it is
confined in MIP samples. By contrast, water confined in larger pores
(MAP) does not exhibit any changes in its relaxation behavior. It
is also shown that the crossover temperature depends on the hydration
level (the higher the hydration level, the lower the crossover temperature).
Below the crossover temperature, we find that water reorientation
is isotropic (NMR) and that the temperature-dependent dielectric relaxation
strength (BDS) follows the tendency expected for a solid-like material.
In contrast, water reorientation is related to long-range diffusion
above the crossover temperature, and the dielectric relaxation strength
follows the tendency expected for a liquid-like material. Furthermore,
the calorimetric results are compatible with crossing a glass transition
near 180 K. Finally, the results are discussed within the Gibbs–Thomson
model. In this framework, the crossover could be related to ice crystals
melting.