Ice formation in micro-droplets

The first indication of the complexity that one may encounter in understanding the freezing of ice came from a set of experiments reported in 1970s by Speedy and Angell [3]. These scientists studied the freezing of micro-droplets of ultra-pure water - the droplets were of a few micrometer (pm) diameter. The reason for choosing such a small size was to avoid the presence of impurities in the sample. Impurities act as seed for crystal nucleation and growth, and have to be avoided if we want to understand the crystallization of pure water. Since it is practically 

The experiments of Speedy and Angell revealed quite a startling result. A few of the samples (which were free of impurities) remained in the liquid state till about -40 °C, where they underwent spontaneous crystallization. That is, pure water droplets can exist in the liquid state till about -40 °C but not any lower Why Nobody really knows the answer for sure yet, but progress is being made. 

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