Temperature-gradient effects on heterogeneous ice nucleation from supercooled water

Investigating the nucleation and freezing behavior of supercooled water under temperature gradients is of significance for theoretical research and practical application. This paper focuses on the freezing temperature of bulk supercooled water in a rectangular container for which the temperature at two sides can be controlled to present a temperature difference. The experimental results show that the nucleation temperature under temperature differences will be lower than that under isothermal conditions. In addition, an increase in the temperature difference is shown to linearly increase the supercooling needed for ice nucleation. The temperature gradient is capable of suppressing heterogeneous ice nucleation. Based on the classical nucleation theory, the free energy barrier for heterogeneous nucleation is attributed to the main factor to affect the nucleation rate. By comparing theoretical evaluations with experimental results, correction on the free energy barrier was conducted to predict the nucleation rate in the temperature gradient. Our experimental research and theoretical correction reveal the nucleation behavior of supercooled water under nonequilibrium conditions.