Molecular Nano-Optics and Spins, Huygens Laboratory, Leiden University, Niels Bohrweg 2, 2333CA Leiden, The Netherlands.
J Phys Chem B. 2009 Dec 3;113(48):15724-9. doi: 10.1021/jp9058388.
We report on micrometer-sized structures in supercooled glycerol observed by imaging fluorescent probes at the temperatures close to, but above, the glass transition temperature (190 K). Two distinct heterogeneous patterns of the fluorescence intensity were detected, depending on how fast the sample was cooled down. In a slowly cooled sample, we observed a Swiss cheese-like pattern in which many micrometer-sized dark spots were nucleated in a bright background. A quickly cooled sample resulted in a spinodal decomposition pattern where many bright island-like features on micrometer scale were dispersed in a dark matrix. Similar patterns were seen earlier in triphenyl phosphite, another molecular liquid, which shows solid-like behavior at temperatures above its glass transition. Once the heterogeneous patterns are formed in the glycerol, they can persist for days, unless the samples are heated above 260 K for more than 10 h. Such heterogeneous patterns are ascribed to differential dye distributions in the glycerol film, pointing to long-lived and micrometer-scale density fluctuations in supercooled glycerol. The observation of such heterogeneity may provide additional understanding on how supercooled glycerol behaves before it turns into a glass.
我们报告了在接近但高于玻璃化转变温度（190 K）的温度下，通过对荧光探针成像观察到的过冷甘油中微米级结构。根据样品冷却速度的不同，检测到两种不同的荧光强度非均相模式。在缓慢冷却的样品中，我们观察到一种瑞士奶酪状的模式，其中许多微米大小的暗点在亮背景中形成。快速冷却的样品则导致了旋节分解模式，其中许多微米尺度的亮岛状特征分散在暗基质中。在三苯基膦氧化物（另一种分子液体）中也观察到了类似的模式，该物质在其玻璃化转变温度以上表现出固态行为。一旦甘油中形成了非均相模式，它们可以持续数天，除非样品在 260 K 以上加热超过 10 小时。这种非均相模式归因于甘油膜中染料的差异分布，表明过冷甘油中存在长寿命和微米级密度涨落。这种不均匀性的观察可能为了解过冷甘油在变成玻璃之前的行为提供了更多的认识。
