Crystal nucleation in colloidal model systems

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The crystallization of a metastable melt is one of the most significant non-equilibrium phenomena of physics. Colloidal model systems have been successfully used for several decades to study fundamental aspects of crystal nucleation and the results have expanded our knowledge about crystallization in an impressive manner.However, a comparison of nucleation rate densities in colloidal hard spheres from experiment and simulation shows a very unsatisfactory result: The absolute values of the nucleation rate densities near freezing diverge between simulation and experiment by up to 12 orders of magnitude. Furthermore, recent studies show a nucleation scenario, which differs significantly from the classical picture. In addition these studies provide initial evidence that the nucleation process is linked in a fundamental way with the physical properties of the meta stable melt.A main aim of the planned project is to identify the oriigin of the huge discrepancy between light scattering and simulation data. For this purpose the crystal nucleation in colloidal hard spheres at low metastability shall be determined using real space microscopy for the first time, whereby some crucial physical properties shall be varied selectively.Moreover, it is planned to determine the structural properties of metastable melt and the crystal nucleation within the metastable melt as a function of metastability in a systematic way. In these studies different colloidal model systems will be used. The obtained results should allow to correlate the physical properties of the melt with the ones of crystal nucleation, giving the possibility to make an important contribution to the fundamental understanding of the crystallization process.