Netsu Sokutei, 49 (3), p. 95, (2022)



Thermal Behavior, Structure, and Dynamics of Water Confined in Mesoporous Silica Glass and Polymer Gel

The properties of water confined in porous materials are different from those of the bulk due to the confinement effect and the interaction with the pore wall of the material. The thermal behavior, structure, and dynamics of water confined in mesoporous silica (MCM-41) and polymer gel (Sephadex G15) were investigated by differential scanning calorimetry (DSC), X-ray scattering, and neutron scattering, respectively. Water confined in MCM-41 with a pore diameter of 21 Å does not freeze even when it is cooled to 180 K. However, the tetrahedral-like network structure of water (ice-like structure) is developed at a low temperature. Furthermore, confined water strongly interacts with the hydrophilic surface of MCM-41 pore. The dynamics of the unfrozen water shows a crossover from non-Arrhenius type behavior to Arrhenius type one, implying a liquid-liquid phase transition. Sephadex G15 has a wide pore size distribution unlike MCM-41. Hence, there are three states of water in the polymer gel: free water, freezable bound water, and unfrozen water. Water molecules in G15 gels are more strongly bound to the hydroxyl groups of the gel matrix compared with the case of the porous silica.