Phase Transition of Nanoconfined Water in Clay: Positron Annihilation, Nuclear Magnetic Resonance, and Dielectric Relaxation Studies

The structural and dynamical features associated with the phase behavior of water confined in clay nanopores (2D confined water) are studied using positron annihilation spectroscopy, nuclear magnetic resonance, and dielectric relaxation spectroscopy techniques. We report the experimental evidence of a new phase transition (above the bulk freezing point of water) in nanoconfined water, in addition to a low-temperature transition in supercooled water. The study reveals it to be a structural rearrangement of water molecules associated with modification of hydrogen-bonded network. Evidence also suggests the dynamical arrest/immobilization of water layer near the clay platelet surface (bould water molecules) to be associated with this transition. This transition is a manifestation of the role of surface interaction on the phase behavior of confined liquids.