On the importance of osmotic interaction during precipitation crystallization

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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.