Water in Confined Space: Study of Density Anomalies and Phase Transitions

Hydrophilic and hydrophobic nano porous materials are utilized to confine water and bypass the homogeneous nucleation. The density anomalies and solid/liquid phase transitions of water at traditionally inaccessible region of phase diagram are studied. The densities versus temperature at ambient pressure of deeply supercooled H2O confined in MCM-41-S and CMK-1 are obtained experimentally by monitoring the Bragg peaks intensity change, which is related to the contrast between matrices and the confined water. Both density maximum and minimum are observed in hydrophilic confinement, however, a delayed to lower temperature density maximum and absence of minimum are shown in hydrophobic system. The deduced thermal expansion coefficients are also revealed different profiles. The thermodynamic and dynamic implications of the maximum in thermal expansion coefficient are critical to scrutinize available theoretical and computational models of water.
In the other part of study, ice Ih and Ic are discovered in a series of hydrophobic porous materials with the pore sizes ranging from 1.9 - 3.8 nm at different temperatures by DSC, XRD, and SAXS. Ice Ic is confirmed to be inside the pores, and obey the Gibbs-Thomson equation.
The results in this dissertation may support the hypothetical liquid-liquid phase transition and shed the road to applications and understandings of water in small spaces.