Dehaoui Amine, Issenmann Bruno, Caupin Frédéric
Institut Lumière Matière, UMR5306 Université Claude Bernard Lyon 1-CNRS, Université de Lyon, Institut Universitaire de France, 69622 Villeurbanne, France.
Institut Lumière Matière, UMR5306 Université Claude Bernard Lyon 1-CNRS, Université de Lyon, Institut Universitaire de France, 69622 Villeurbanne, France
Proc Natl Acad Sci U S A. 2015 Sep 29;112(39):12020-5. doi: 10.1073/pnas.1508996112. Epub 2015 Sep 16.
The viscosity of a liquid measures its resistance to flow, with consequences for hydraulic machinery, locomotion of microorganisms, and flow of blood in vessels and sap in trees. Viscosity increases dramatically upon cooling, until dynamical arrest when a glassy state is reached. Water is a notoriously poor glassformer, and the supercooled liquid crystallizes easily, making the measurement of its viscosity a challenging task. Here we report viscosity of water supercooled close to the limit of homogeneous crystallization. Our values contradict earlier data. A single power law reproduces the 50-fold variation of viscosity up to the boiling point. Our results allow us to test the Stokes-Einstein and Stokes-Einstein-Debye relations that link viscosity, a macroscopic property, to the molecular translational and rotational diffusion, respectively. In molecular glassformers or liquid metals, the violation of the Stokes-Einstein relation signals the onset of spatially heterogeneous dynamics and collective motions. Although the viscosity of water strongly decouples from translational motion, a scaling with rotational motion remains, similar to canonical glassformers.
液体的粘度衡量其对流动的阻力，这对液压机械、微生物的运动以及血管中血液的流动和树木中树液的流动都会产生影响。冷却时粘度会急剧增加，直至达到玻璃态时动力学停滞。水是出了名的难以形成玻璃态的物质，过冷液体很容易结晶，这使得测量其粘度成为一项具有挑战性的任务。在此我们报告接近均匀结晶极限的过冷水的粘度。我们的值与早期数据相矛盾。一个单一的幂律可再现直至沸点粘度50倍的变化。我们的结果使我们能够检验将粘度这一宏观性质分别与分子平移扩散和旋转扩散联系起来的斯托克斯 - 爱因斯坦关系以及斯托克斯 - 爱因斯坦 - 德拜关系。在分子玻璃形成体或液态金属中，斯托克斯 - 爱因斯坦关系的违背标志着空间非均匀动力学和集体运动的开始。尽管水的粘度与平移运动强烈解耦，但与旋转运动的标度关系仍然存在，类似于典型的玻璃形成体。
