[M-IS12] Interface- and nano-phenomena on crystal growth and dissolution

[MIS12-06] Why does the growth rate of an ice crystal oscillate periodically under microgravity conditions?

*Hitoshi Miura¹, Yoshinori Furukawa² (1.Graduate School of Science, Department of Information and Basic Science, Nagoya City University, 2.Institute of Low Temperature Science, Hokkaido University)

Keywords:Ice crystal, Melt growth, Antifreeze glycoprotein, Growth rate, Oscillation, Microgravity

Fish and insects inhabiting cold regions protect themselves from freezing of body fluids by synthesizing proteins in their bodies that inhibit the growth of ice crystals. These proteins are called antifreeze protein (AFP), including antifreeze glycoprotein (AFGP), and are expected to be applied to various fields related to water freezing phenomena. In order to clarify the effect of AFGP on ice crystal growth from the viewpoint of crystal growth, the Ice Crystal 2 project was conducted on the International Space Station (ISS) in 2013-2014 to observe an ice crystal basal plane growing in supercooled water at molecular levels [1]. The normal growth rate of the basal plane growing in supercooled water containing AFGP was analyzed, and it was found that the normal growth rate spontaneously oscillated with a period of about 10 seconds (spontaneous oscillatory growth), even though the supercooling was set to a constant value of 0.3 K by the equipment. The normal growth rate showed a behavior of switching between two phases, fast growth and slow growth, in a short period of time. The normal growth rate was smaller than that in pure water (without AFGP) in the slow-growth phase, in contrary, significantly larger than that in pure water in the fast-growth phase. The mechanism by which AFGP promotes growth in the fast-growth phase has been proposed to be heterogeneous two-dimensional nucleation by AFGP adsorbed on the basal plane [1]. However, the mechanism that causes the spontaneous oscillatory growth is not known at all. In this study, we modeled the heterogeneous two-dimensional nucleation activity of AFGP adsorbed on the basal plane and discussed the theoretical mechanism of the spontaneous oscillatory growth. We found that the spontaneous oscillatory growth is triggered by the release of latent heat of crystallization, and that the background of the repeated oscillations is the existence of a discontinuous branching structure (catastrophe) due to the interdependence between the amount of AFGP adsorbed on the basal plane and the normal growth rate. This result indicates that the nucleation activity of AFGP, which has been only a theoretical hypothesis, may be related to the nature of the action of AFGP on the growth of ice crystals.

Reference: [1] Furukawa et al., Sci. Rep. 7, 43157 (2017)