On the importance of osmotic interaction during precipitation crystallization

结晶过程在几毫秒和几秒的范围内形成细小的、极易溶解的结晶相的过程称为沉淀结晶过程。由于沉淀产物的低溶解度，只有在高过饱和度下进行该过程才有可能进行经济生产。在这样的条件下，成核和生长等固体形成过程的速度非常快。必须明确颗粒形成机制的关键步骤，才能预测最终颗粒的性质(颗粒大小分布、形态等)。通过沉淀可以获得的典型颗粒尺寸在20纳米到10微米之间。因此，在足够高的过饱和度水平下，固体沉淀是制备纳米颗粒的方法之一。这些颗粒会经历一系列的二次过程，如团聚、再结晶和老化，这些过程会显著影响最终得到的沉淀物的性质。本研究的目的是澄清这样一个假设，即在颗粒生长过程中，渗透相互作用对一次颗粒的聚集是重要的。初步估计，这种吸引人的相互作用相对较强且范围较短。在文献中，还没有关于沉淀过程中渗透相互作用及其对颗粒形成的影响的报道。同步辐射同轴X射线衍射是研究这一效应的一种很有前途的实验方法。与其他实验方法相结合的X射线衍射测量应采用适当的建模方法进行解释。为此目的，现有的研究沉淀过程的同轴X射线衍射法必须超越其目前的状态。研究的重点是对降水过程中粒子形成的时间分辨观测及其对渗透相互作用的定性和定量理解的解释。

Crystallization processes which form a fine, sparingly soluble, crystalline phase at process times which are in the range of milliseconds and seconds are called precipitation crystallization processes. Due to the low solubility of the precipitated products economic production is only possible, if the process is performed at high supersaturation. Under such conditions, solid formation processes as nucleation and growth run very high rates. Crucial steps of the particle formation mechanism must be clear for being able to make predictions about the final particle properties (particle size distribution, morphology, etc.). Typical particle sizes that can be obtained by precipitation, are between 20 nm and 10 microns. Thus, at sufficiently high supersaturation levels precipitation of solids is one of the methods for producing nanoparticles. These particles can pass through a series of secondary processes such as agglomeration, recrystallization and aging, which can significantly affect the properties of the finally obtained precipitate.The aim of this research proposal is to clarify the hypothesis that during particle growth osmotic interaction is of importance for aggregation of primary particles. Preliminary estimation characterizes this attractive interaction to be comparatively strong and of short-range. In literature the osmotic interaction and its influence on particle formation during the precipitation has not yet been reported. In-line X-ray diffraction with synchrotron radiation is a promising experimental method for investigating this effect. X-ray diffraction measurements combined with other experimental methods shall be interpreted with appropriate modeling approaches. To this end the existing in-line X-ray diffraction method for the investigation of precipitation processes has to be developed beyond its current status. The focus of the investigation is on the time-resolved observation of particle formation during precipitation processes and their interpretation with respect to the a qualitative and quantitative understanding of the osmotic interaction.