Freezing of Heavy Water (D₂O) Nanodroplets

Abstract

We follow the freezing of heavy water (D₂O) nanodroplets formed in a supersonic nozzle apparatus using position resolved pressure trace measurements, Fourier transform infrared spectroscopy, and small-angle X-ray scattering. For these 3–9 nm radii droplets, freezing starts between 223 and 225 K, at volume based ice nucleation rates <i>J</i>_ice,V on the order of 10²³ cm^–3 s^–1 or surface based ice nucleation rates <i>J</i>_ice,S on the order of 10¹⁶ cm^–2 s^–1. The temperatures corresponding to the onset of D₂O ice nucleation are higher than those reported for H₂O by Manka et al. [Manka, A.; Pathak, H.; Tanimura, S.; Wölk, J.; Strey, R.; Wyslouzil, B. E. <i>Phys. Chem. Chem. Phys.</i> <b>2012</b>, <i>14</i>, 4505]. Although the values of <i>J</i>_ice,S scale somewhat better with droplet size than values of <i>J</i>_ice,V, the data are not accurate enough to state that nucleation is surface initiated. Finally, using current estimates of the thermophysical properties of D₂O and the theoretical framework presented by Murray et al. [Murray, B. J.; Broadley, S. L.; Wilson, T. W.; Bull, S. J.; Wills, R. H.; Christenson, H. K.; Murray, E. J. <i>Phys. Chem. Chem. Phys.</i> <b>2010</b>, <i>12</i>, 10380], we find that the theoretical ice nucleation rates are within 3 orders of magnitude of the measured rates over an ∼15 K temperature range