FREEZING OP WATER IN W/O EMULSIONS

A short review is given on the freezing of water in w/o emulsions. First the state of supercooled water is discussed. The quantitative treatment of the liquid-solid phase transition in supercooled water is given by the homogeneous nucleation theory. From the experimental methods, which are used to study supercooled water, only few are applicable to the liquid-solid phase transition. From these methods electron microscopy, thermal analysis and EFE are chosen to reveal some characteristic features of freezing of water in w/o emulsions. At the end of the paper the production of vitreous water by jet-freezing of w/o emulsions is reported. It is shown that especially the role of the surfactant molecules, which are necessary to stabilize emulsions with urn-sized droplets, is not understood in the liquid-solid transition. The possibility of reaching the homogeneous nucleation temperature of -40 C in w/o emulsions (and also the fact, that water can be vitrified in w/o emulsions using small cooling rates of 10¹² 10⁶ C/sec compared to the estimated necessary rate of 1012 C/sec), may not only oe caused by a statistical effect leading to the negligibility of heterogeneous nuclei, but also by some surfactant effects influencing the formation of homogeneous nuclei.