4:30 PM - 4:45 PM
[MIS18-08] Multi-step nucleation model from water vapor to ice
Keywords:nucleation, water, ice, condensation
Regarding the phase transition from gas to solid, solidification and crystallization occur immediately in the supersaturated state in the case of heterogeneous nucleation that condenses on a substrate or an impurity, the picture is very different in the case of homogeneous nucleation. For example, the formation of supercooled liquid has been observed even at temperatures below the triple point where crystallization is expected for many materials such as in water and minerals1-4). In particular, supercooled water droplets up to -40°C have been observed in Earth’s upper atmosphere, but the mechanism is still not well understood. The phenomenon in which a phase with thermodynamically high free energy appears first, followed by the appearance of a stable phase is called Ostwald's step rule, and has been observed experimentally and also by molecular dynamics simulations. However, theoretical models for condensation and crystallization processes in such non-equilibrium conditions are still lacking. In this study, we investigate the multi-step nucleation of water vapor using a theoretical model that takes into account condensation nucleation from the gas phase and the crystallization process of supercooled droplets.
For condensation nucleation of water vapor, we used a highly accurate theoretical model of nucleation (called the SP model) proposed from nucleation experiments and molecular dynamics simulations 5) . On the other hand, for the crystallization process of supercooled water droplets, we used a recently proposed crystallization model that unifies the experimental results of crystallization temperature of supercooled water droplets under various cooling rates 6). By combining these two models describing condensation nucleation and crystallization of supercooled water droplets, we performed theoretical calculations. As a result, we obtain the condensation temperature, size of supercooled water droplets, and crystallization temperature of water droplets during the cooling process. For large cooling rates, both the condensation and crystallization temperatures decrease, and the droplet and ice crystal sizes also decrease. For a wide range of cooling rates, water vapor does not crystallize immediately after condensation, but first forms supercooled droplets and then solidifies after further cooling. Our results imply that multistep nucleation is a common first stage of condensation from water vapor to solid.
Reference
1) Manka et al. Phys. Chem. Chem. Phys. 14(2012)4505
2) Kimura et al. Cryst. Growth Des.12(2012)3278
3) Ishizuka et al. The Astrophys. J.803(2015) 88
4) Tanaka et al. Phys. Rev. E 96(2017) 022804
5) Angelil et al. J.Chem.Phys. 143(2015),064507
6) Tanaka and Kimura, Phys. Chem. Chem. Phys., 21(2019) 2410
For condensation nucleation of water vapor, we used a highly accurate theoretical model of nucleation (called the SP model) proposed from nucleation experiments and molecular dynamics simulations 5) . On the other hand, for the crystallization process of supercooled water droplets, we used a recently proposed crystallization model that unifies the experimental results of crystallization temperature of supercooled water droplets under various cooling rates 6). By combining these two models describing condensation nucleation and crystallization of supercooled water droplets, we performed theoretical calculations. As a result, we obtain the condensation temperature, size of supercooled water droplets, and crystallization temperature of water droplets during the cooling process. For large cooling rates, both the condensation and crystallization temperatures decrease, and the droplet and ice crystal sizes also decrease. For a wide range of cooling rates, water vapor does not crystallize immediately after condensation, but first forms supercooled droplets and then solidifies after further cooling. Our results imply that multistep nucleation is a common first stage of condensation from water vapor to solid.
Reference
1) Manka et al. Phys. Chem. Chem. Phys. 14(2012)4505
2) Kimura et al. Cryst. Growth Des.12(2012)3278
3) Ishizuka et al. The Astrophys. J.803(2015) 88
4) Tanaka et al. Phys. Rev. E 96(2017) 022804
5) Angelil et al. J.Chem.Phys. 143(2015),064507
6) Tanaka and Kimura, Phys. Chem. Chem. Phys., 21(2019) 2410