Li Qi, Kölbel Johanna, Davis Margaret P, Korter Timothy M, Bond Andrew D, Threlfall Terrence, Zeitler J Axel
Department of Chemical Engineering and Biotechnology, University of Cambridge, Philippa Fawcett Drive, Cambridge CB3 0AS, U.K.
Department of Chemistry, Syracuse University, 1-046 Center for Science and Technology, Syracuse, New York 13244, United States.
Cryst Growth Des. 2022 Jun 1;22(6):3961-3972. doi: 10.1021/acs.cgd.2c00352. Epub 2022 May 20.
Terahertz time-domain spectroscopy in a transmission geometry combined with visual analysis was used to investigate the crystallization process of MgSO solution. Careful spectral analysis of both a feature at 1.6 THz and the overall magnitude of absorption allowed the extraction of information about the liquid phase before and during crystallization, aiding the investigation of solvation dynamics and the behavior of molecular species at phase boundaries. The method was reproducibly applied to a number of measurements on a series of solutions of three chosen concentrations at different temperatures. When increasing temperature at the end of the measurement, the dissolution of crystals was observed as well. The temperature-dependent absorption data of the semicrystalline systems were converted to the solvent concentrations using a recently developed method. Solutions of a series of concentrations were also investigated in the temperature range of 4-25 °C. The results were compared to the theoretical calculated values, and the consistent differences proved the existence of a hydration shell around the salt ions whose behavior is different from bulk water. Future work will focus on triggering nucleation at specific positions in order to study the very beginning of the crystallization process. MgSO heptahydrate is used as a model system in this study, while the concept and the setup can be applied to other systems.
采用透射几何结构的太赫兹时域光谱结合视觉分析来研究硫酸镁溶液的结晶过程。对1.6太赫兹处的特征峰和吸收的整体幅度进行仔细的光谱分析，有助于提取结晶前和结晶过程中液相的信息，辅助研究溶剂化动力学以及相界处分子物种的行为。该方法可重复应用于对一系列不同温度下三种选定浓度溶液的多次测量。在测量结束时升高温度时，还观察到了晶体的溶解。使用最近开发的方法将半结晶体系的温度依赖性吸收数据转换为溶剂浓度。还在4 - 25°C的温度范围内研究了一系列浓度的溶液。将结果与理论计算值进行比较，一致的差异证明了盐离子周围存在水合壳，其行为与 bulk 水不同。未来的工作将集中在触发特定位置的成核，以研究结晶过程的最初阶段。本研究中使用七水硫酸镁作为模型体系，而该概念和装置可应用于其他体系。
