Niehaus Joseph, Cantrell Will
Atmospheric Sciences Program and Department of Physics, Michigan Technological University , 1400 Townsend Drive, Houghton, Michigan 49931, United States.
J Phys Chem Lett. 2015 Sep 3;6(17):3490-5. doi: 10.1021/acs.jpclett.5b01531. Epub 2015 Aug 25.
Water is unlikely to crystallize homogeneously at temperatures greater than -34 °C. Freezing at higher temperatures is heterogeneous-catalyzed by the presence of a second substance. If that substance is at an air-water interface, then the mode is called contact freezing, and it typically will trigger nucleation at a higher temperature than if the substance were wholly immersed within the liquid. We find that the impact of salt particles initiates freezing in experiments using water droplets at supercoolings of 9 to 16 °C. These results show that contact freezing nuclei need not be effective as immersion mode nuclei. We discuss our results in the context of proposed mechanisms of contact freezing. Finally, we use the time scales for diffusion of heat and of ions and the propagation of a sound wave through the droplet to estimate that contact freezing occurs within 10 ns of impact.
在温度高于-34°C时，水不太可能均匀结晶。在较高温度下结冰是由第二种物质的存在非均相催化的。如果该物质处于气-水界面，那么这种模式就称为接触冻结，与该物质完全浸没在液体中相比，它通常会在更高的温度下引发成核。我们发现在使用过冷水滴的实验中，盐颗粒的撞击会在9至16°C的过冷度下引发冻结。这些结果表明，接触冻结核作为浸没模式核不一定有效。我们在接触冻结的提出机制的背景下讨论我们的结果。最后，我们利用热和离子扩散的时间尺度以及声波在液滴中的传播来估计接触冻结在撞击后10纳秒内发生。
