Abstract
Freezing, melting, evaporation and condensation of water are essential ingredients for climate and eventually life on Earth. In the present work, we show how surface freezing of supercooled water in an open container is conditioned and triggered—exclusively—by humidity in air. Additionally, a change of phase is demonstrated to be triggered on the water surface forming surface ice crystals prior to freezing of bulk. The symmetry of the surface crystal, as well as the freezing point, depend on humidity, presenting at least three different types of surface crystals. Humidity triggers surface freezing as soon as it overpasses a defined value for a given temperature, generating a plurality of nucleation nodes. An evidence of simultaneous nucleation of surface ice crystals is also provided.
Highlights
Nakaya demonstrated that snow crystals grow in cold humid air as a large variety of mainly plane crystals depending on both temperature and humidity of air 80 years ago (Magono and Woo 1966)
In all cases freezing is triggered at the certain point as shown in Fig. 2 wherein freezing points of water droplets previously obtained in reference (PerezDiaz et al 2016) have been plotted
It is evident that freezing points of water in an open container fit perfectly in the curve defined by those of droplets, demonstrating that this phenomenon does not depend on the geometry of the surface
Summary
Nakaya demonstrated that snow crystals grow in cold humid air as a large variety of mainly plane crystals depending on both temperature and humidity of air 80 years ago (Magono and Woo 1966). As they were formed by inverse sublimation from vapor nobody got surprised that humidity—i.e. water vapor concentration in air—had a role on the kind of crystal grown. More recently 2D confined water and ice crystals have attracted the attention of researchers They are described to appear between two solid layers (Chen et al 2015) with a structure depending on pressure and width (Zangi and Mark 2003). First neighboring oxygens and H-bonds in supercooled water and Hydrophobicity and hydrophilicity of surfaces confining liquid water seem to modulate its density at the nanoscale (Giovambattista et al 2007), presenting a larger diffusivity when confined in mesopores by hydrophobic surfaces (Aso et al 2012) and “ab initio” computations demonstrate a phase change in nano-confined ice from a honeycomb to square under pressure depending on the hydrophobicity/hydrophilicity of such surfaces (Corsetti et al 2016)
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