Bio-Acoustic-Microelectromechanical Systems in Medicine Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Center for Bioengineering, Boston, MA 02115, USA.
Proc Natl Acad Sci U S A. 2010 Mar 9;107(10):4596-600. doi: 10.1073/pnas.0914059107. Epub 2010 Feb 22.
The vitrification of a liquid occurs when ice crystal formation is prevented in the cryogenic environment through ultrarapid cooling. In general, vitrification entails a large temperature difference between the liquid and its surrounding medium. In our droplet vitrification experiments, we observed that such vitrification events are accompanied by a Leidenfrost phenomenon, which impedes the heat transfer to cool the liquid, when the liquid droplet comes into direct contact with liquid nitrogen. This is distinct from the more generally observed Leidenfrost phenomenon that occurs when a liquid droplet is self-vaporized on a hot plate. In the case of rapid cooling, the phase transition from liquid to vitrified solid (i.e., vitrification) and the levitation of droplets on liquid nitrogen (i.e., Leidenfrost phenomenon) take place simultaneously. Here, we investigate these two simultaneous physical events by using a theoretical model containing three dimensionless parameters (i.e., Stefan, Biot, and Fourier numbers). We explain theoretically and observe experimentally a threshold droplet radius during the vitrification of a cryoprotectant droplet in the presence of the Leidenfrost effect.
当冰晶在低温环境中通过超快冷却而防止形成时，液体就会发生玻璃化。一般来说，玻璃化需要液体与其周围介质之间存在较大的温差。在我们的液滴玻璃化实验中，我们观察到当液滴直接与液氮接触时，这种玻璃化事件伴随着莱顿弗罗斯特现象，这会阻碍传热以冷却液体。这与更常见的在热板上发生的莱顿弗罗斯特现象不同，在这种现象中，液滴会自行蒸发。在快速冷却的情况下，从液体到玻璃态固体的相变（即玻璃化）和液滴在液氮上的悬浮（即莱顿弗罗斯特现象）同时发生。在这里，我们通过使用包含三个无量纲参数（即斯蒂芬、比奥和傅立叶数）的理论模型来研究这两个同时发生的物理事件。我们从理论上解释并从实验上观察到，在莱顿弗罗斯特效应存在的情况下，抗冻剂液滴玻璃化过程中的液滴临界半径。
