Reichenbach Judith, Wynne Klaas
School of Chemistry , University of Glasgow , Glasgow G12 8QQ , U.K.
J Phys Chem B. 2018 Aug 2;122(30):7590-7596. doi: 10.1021/acs.jpcb.8b04112. Epub 2018 Jul 19.
Gibbs classical nucleation theory predicts that a supersaturated solution will have transient nuclei that flitter in and out of existence. Only when one of these nuclei becomes larger than a critical size, will the solution crystalize. Recently, nonclassical nucleation theories have invoked the presence of prenuclei possibly associated with a liquid-liquid phase separation. However, there are few experimental observations of such prenuclei. Here, we use ultrafast optical Kerr-effect spectroscopy to measure the temperature-dependent low-frequency (sub-gigahertz to terahertz) anisotropic Raman spectra of supersaturated aqueous sodium thiosulfate solutions. Clear evidence of clusters is obtained in the spectra. However, on the basis of the inferred stability of these clusters, it appears that they frustrate rather than promote the formation of crystals. This would explain the surprising stability of supersaturated sodium thiosulfate and similar solutions.
吉布斯经典成核理论预测，过饱和溶液会有瞬间形成又瞬间消失的瞬态晶核。只有当这些晶核中的某一个变得大于临界尺寸时，溶液才会结晶。最近，非经典成核理论提出了可能与液-液相分离相关的预核的存在。然而，此类预核的实验观测结果很少。在这里，我们使用超快光学克尔效应光谱来测量过饱和硫代硫酸钠水溶液的温度依赖性低频（亚吉赫兹到太赫兹）各向异性拉曼光谱。在光谱中获得了团簇的明确证据。然而，基于这些团簇的推断稳定性，它们似乎阻碍而非促进晶体的形成。这可以解释硫代硫酸钠过饱和溶液及类似溶液令人惊讶的稳定性。
