The Molecular Dynamics Study of the Molecular Structure of Highly Concentrated Aqueous Solution and the Control of Crystallization

本研究的目的是阐明高浓度电解质水溶液的分子结构，并利用分子动力学模拟在分子水平上解释宏观测量的性质，如溶解度或压降。对于液体的计算机模拟，在简单液体的情况下，例如液体稀有气体，其中粒子之间的相互作用是众所周知的，模拟得到的结果值得高度可靠。另一方面，在复杂液体的情况下，这些液体还没有经过分析处理。它们可以预测不能或不能直接测量的液体的性质，同时需要进行各种可靠性测试。研究内容和结果如下：1.研究内容和成果。分子结构的J4D计算与EXAFS分析的比较研究了溴化锂和溴化钾等混合电解质水溶液中BR周围的结构。用简化的对势计算结果与实验结果吻合较好。即使有一个简化的势，分子动力学模拟也给出了定量的结构特征。宏观测量性质的预测当溶液的浓度超过溶解度时，汽相和液体同时存在的计算域是有效的。由于系统的压力与饱和蒸汽压相同，因此不需要对压力进行控制。计算了溶液表面的密度分布或表面张力等性质，并估算了压降。对吸收过程和结晶过程进行了分子动力学模拟，研究了水蒸气吸收过程中溶液表面的状态以及非平衡态对吸收速率的影响。结晶过程的模拟是下一个主题。

The objectives of this study are to clarify the molecular structure of the highly concentrated aqueous electrolyte solution and to explain the macroscopically measured properties, such as solubility or pressure drop, on a molecular level using molecular dynamics simulation. As for liquid computer simulation, in the case of simple liquid, say liquid noble gases, where interactions between particles are well known, the results derived from the simulation deserve high degree of reliability. On the other hand, in the case of complicated liquid, which have not yet been treated analytically. They can predict the properties of liquid which cannot or not directly be measured and at the same time various tests of reliability are required. The contents and results are as follows.1. Comparison between J4D calculation and EXAFS analysis about molecular structureIn the mixture of aqueous electrolyte solutions, such as LiBr & KBr, the structure around Br was investigated. The calculation results using simplified pair potentials well agree with experimental ones. Even with a simplified potential, molecular dynamics simulation gives quantitative structural features.2. Prediction of the macroscopically measured propertiesWhen the concentration of a solution is over the solubility, the computational domain in which both vapor and liquid exist is effective. Because the pressure of the system is the same to the saturation vapor pressure, the control of pressure is not needed. The properties of a solution surface, such as density profile or surface tension, were calculated and the pressure drop was estimated.3. The MD simulation of absorption process and crystallization process The state of the solution surface during water vapor absorption and the effects of the non-equilibrium state on absorption rate were investigated. The simulation of a crystallization process is the next theme.