Ice-Water Equilibrium in Nanoscale Confinement

We show that 2D 2H NMR spectra enable valuable insights into the nature of an ice -water equilibrium in nanoscale confinement, which extends over a broad temperature range. In particular, 2D 2H NMR lineshape analysis allows us to determine the timescale on which the coexisting ice and water phases exchange molecules. For D2O in a silica nanopore with a diameter of 5.4 nm, we find that the residence time of a water molecule in either phase is characterized by an NMR exchange time of tau X 1/4 5.7 ms at 220 K. Thus, the ice -water equilibrium is highly dynamic, which is an important aspect for an understanding of deeply cooled confined and, possibly, bulk waters.