Molecular dynamics simulation of gas liquid nucleation in aqueous systems.

近几十年来，气相成核的研究得到了很大的发展。其原因是与技术应用相关的，成核过程理论和模拟的进一步发展，以及相形成早期状态研究的实验技术的发展。本项目的目的是研究二元体系中成核的微观效应，并将其与通常的宏观实验观察联系起来。二元体系的选择，以涵盖范围从高度对称的强烈不对称的混合物。此外，相关的技术应用以及实验数据的存在被认为是。基于这些判据及其广泛的普遍意义，本文选择了以水为组分的二元体系来研究二元成核。首先研究水和重水的混合物。除了质量不同外，重水的相互作用参数也略有不同。对于这个高度对称的系统，成核速率和临界团簇摩尔分数的实验数据是可用的。在这样的对称系统中的成核分析是必要的，以获得数据来评估成核理论在对称极限的一致性。在本项目中获得的微观和宏观数据将用于此目的。相比之下，甲烷/水系统是非常不对称的系统。它与诸如基于二元成核过程的天然气干燥过程的技术应用相关。由于丁醇的极性，由水和1-丁醇组成的第三系统比甲烷/水系统更不对称。该系统是特别感兴趣的，因为除了成核速率之外，形成液滴的结构的实验数据也是可用的。除了含水系统对称性的变化外，还应分析压力对成核的影响。这对于涉及高压成核的技术过程是重要的。调查将集中在那些系统，它是已知的，他们的集群结构偏离预期的体相行为。这些偏差可能源于一种物质在簇表面的优选吸附，或者源于液-液不相容性的形成，其在体相中不以这种形式存在。为了分析二元成核，应开发一种方法，用于构建作为分子A和B数量函数的形成功的二元平面。用这种方法的统计成核，集群的增长，蒸发将进行评估。

The research on nucleation from the vapour phase has been developed significantly in the last decades. Reasons are the relevance for technical applications, the further development of theory and simulation of nucleation processes and the development of experimental techniques for the investigation of early states of phase formation.The aim of this project is to investigate the microscopic effects on nucleation in binary systems and to relate them to the usually macroscopic experimental obser¬vations. The binary systems are selected to cover the range from highly symmetric to strongly asymmetric mixtures. In addition, the relevance for technical applications as well as the existence of experimental data is considered. Based on these criteria and its broad general significance binary systems with water as component are chosen here for the investigation of binary nucleation.First mixtures of water and heavy water will be investigated. Besides its different mass heavy water also has slightly different interaction parameters. For this highly symmetric system experimental data for nucleation rates and critical cluster mole fraction are available. The analysis of nucleation in such symmetric systems is necessary to obtain data to evaluate the consistency of nucleation theories in the symmetric limit. The microscopic and macroscopic data that will be obtained in this project will be employed for this purpose among others. The system methane/water is in contrast a very asymmetric system. It is relevant for technical applications such as a drying process of natural gas based on a binary nucleation process. The third system consisting of water and 1-butanol is less asymmetric than the methane/water system due to the polarity of butanol. This system is of special interest as besides the nucleation rates, also experimental data of the structure of forming droplets are available. In addition to the variations of the symmetry of the aqueous systems also the influence of pressure on the nucleation shall be analysed. This is of importance for technical processes involving high pressure nucleation. Investigations will be focused on those systems for which it is known that their cluster structure deviates from what is expected from the bulk phase behaviour. These deviations can originate from the preferred adsorption of one species at the cluster surface or from the formation of a liquid-liquid immiscibility, which does not exist in this form in the bulk phase. For the analysis of binary nucleation a method for the construction of the binary plane of the work of formation as function of the number of molecules A and B shall be developed. With this method the statistics of nucleation, cluster growth, and evaporation will be evaluated.