Flash freezing
[1] This is done by subjecting an object to cryogenic temperatures, or through direct contact with liquid nitrogen at −196 °C (−320.8 °F).
Flash freezing is commonly applied in the food industry and is studied in atmospheric science.
This results in much less damage to cell walls, proportional to the rate of freezing.
In this case, food items are subjected to temperatures well below[clarification needed] the freezing point of water.
Thus, smaller ice crystals are formed, causing less damage to cell membranes.
[5] This is done by submerging the sample in liquid nitrogen or a mixture of dry ice and ethanol.
[6] Flash freezing is of great importance in atmospheric science, as its study is necessary for a proper climate model for the formation of ice clouds in the upper troposphere, which effectively scatter incoming solar radiation and prevent Earth from becoming overheated by the Sun.
One of the current debates is whether the formation of ice occurs near the surface or within the micrometre-sized droplets suspended in clouds.
If it is the former, effective engineering approaches may exist to tune the surface tension of water so that the ice crystallization rate can be controlled.
[7] The surface environment does not play a decisive role in the formation of ice and snow.
[9] There are phenomena like supercooling, in which the water is cooled below its freezing point but remains liquid if there are too few defects to seed crystallization.
[11] The crystallization of ice from supercooled water is generally initiated by a process called nucleation.
However, this remaining liquid water crystallizes too fast for its properties to be detected or measured.
[11] The freezing speed directly influences the nucleation process and ice crystal size.
[8] Once the liquid is completely frozen, the sharp tip of the drop attracts water vapor in the air, much like a sharp metal lightning rod attracts electrical charges.
[8] The water vapor collects on the tip and a tree of small ice crystals starts to grow.
[8] An opposite effect has been shown to preferentially extract water molecules from the sharp edge of potato wedges in the oven.
[11] The change in the structure of water controls the rate at which ice forms.
Crystal growth or nucleation is the formation of a new thermodynamic phase or a new structure via self-assembly.
This can also be observed in the nucleation of ice in supercooled small water droplets.
It correctly predicts that the time needed for nucleation decreases extremely rapidly when supersaturated.
In this case, part of the nucleus boundary is accommodated by the surface or impurity onto which it is nucleating.
