Ice-Water Equilibrium in Nanoscale Confinement

We show that 2D $^{2}\mathrm{H}$ 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 $^{2}\mathrm{H}$ NMR line-shape analysis allows us to determine the timescale on which the coexisting ice and water phases exchange molecules. For ${\mathrm{D}}_{2}\mathrm{O}$ 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 ${\ensuremath{\tau}}_{\mathrm{X}}=5.7\text{ }\text{ }\mathrm{ms}$ 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.