Spontaneous oscillatory growth of ice crystals in supercooled water under a microgravity environment: Theoretical hypothesis on the effect of antifreeze glycoprotein

In a crystal growth experiment conducted on the Japanese Experiment Module "Kibo"aboard the International Space Station, an unknown phenomenon, i.e., spontaneous oscillation of the growth rate of ice-crystal basal faces in supercooled water containing antifreeze glycoprotein (AFGP), was observed. In this study, we modeled growth-inhibiting and growth-promoting effects of the AFGP adsorbed on the ice-crystal basal face and discussed the mechanism of the spontaneous oscillatory growth. The normal growth rate of the basal face depends on the amount of AFGP adsorbed on the basal face. Simultaneously, the amount of adsorbed AFGP is controlled by the crystal growth, because the higher the growth rate, the more frequently the crystal surface is renewed. The normal growth rate and the amount of adsorbed AFGP can be determined as a steady state that satisfies the interdependence between these quantities. By formulating the interdependence and finding the steady state, we demonstrated the appearance of two different stable steady states in a certain range of supercooling (bistability). This is theoretical proof of a crystal growth hysteresis, in which the trace of the growth rate varies with when the degree of supercooling is increased or decreased. We also clarified that the spontaneous oscillation of the growth rate is triggered by the release of the latent heat of crystallization. Our findings herein provide novel possibilities for the effect of AFGP on ice-crystal growth.