Physical origins of freezing and melting temperature depressions of water in millimeter-sized pores

Abstract

As a long-standing problem, the physics of freezing and melting temperature depressions of water in millimeter-sized pores remains elusive. We devised a series of experiments on the freezing and melting of water in glass tubes with varying tube diameters, water volumes, water-solid interfacial areas, and cooling rates. The results of the experiments indicate that the freezing temperature depression is highly correlated with the water-solid interfacial areas. It can be inferred that heterogeneous nucleation is the dominant physical origin for such freezing temperature depression. In contrast, melting temperature depression is orders of magnitude lower than that of freezing, and is independent of heating rate, water volume, water-solid interfacial area, and correlated with pore diameter, suggesting the governing role of capillarity. The recognized distinct physical origins of freezing and melting temperatures lead to the disparity between them, i.e., freezing and melting hysteresis. The findings resolve the controversy on the freezing mechanism of water in millimeter-sized pores, and can be used to better manipulate freezing and melting behaviors of pore water in various engineering applications, e.g., promoting or inhibiting freezing in biomaterials, and developing anti-freezing materials.