Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot, 76100, Israel.
Science. 2010 Feb 5;327(5966):672-5. doi: 10.1126/science.1178085.
Although ice melts and water freezes under equilibrium conditions at 0 degrees C, water can be supercooled under homogeneous conditions in a clean environment down to -40 degrees C without freezing. The influence of the electric field on the freezing temperature of supercooled water (electrofreezing) is of topical importance in the living and inanimate worlds. We report that positively charged surfaces of pyroelectric LiTaO3 crystals and SrTiO3 thin films promote ice nucleation, whereas the same surfaces when negatively charged reduce the freezing temperature. Accordingly, droplets of water cooled down on a negatively charged LiTaO3 surface and remaining liquid at -11 degrees C freeze immediately when this surface is heated to -8 degrees C, as a result of the replacement of the negative surface charge by a positive one. Furthermore, powder x-ray diffraction studies demonstrated that the freezing on the positively charged surface starts at the solid/water interface, whereas on a negatively charged surface, ice nucleation starts at the air/water interface.
尽管在 0°C 的平衡条件下冰会融化，水会结冰，但在清洁环境的均相条件下，水可以被过冷至-40°C 而不结冰。电场对过冷水冰点（电冷冻）的影响在生命和无生命世界中都具有重要意义。我们报告说，热释电 LiTaO3 晶体和 SrTiO3 薄膜的带正电荷表面促进冰核形成，而带负电荷的相同表面则降低冰点。因此，当带负电荷的 LiTaO3 表面上冷却的水滴在 -11°C 下仍为液态，当该表面加热到-8°C 时，由于负表面电荷被正电荷取代，水立即冻结。此外，粉末 X 射线衍射研究表明，带正电荷表面上的冻结始于固/水界面，而在带负电荷的表面上，冰核形成始于气/水界面。
