Crystal nucleation in colloidal model systems

亚稳熔体的结晶是物理学中最重要的非平衡现象之一。几十年来，胶体模型系统已经成功地用于研究晶体成核的基本方面，其结果以令人印象深刻的方式扩展了我们对结晶的认识。然而，将实验和模拟的胶体硬球的成核率密度进行比较，结果并不令人满意：模拟和实验在冻结附近的成核率密度绝对值相差高达12个数量级。此外，最近的研究显示了一个与经典图像有很大不同的成核情景。此外，这些研究提供了初步证据，表明成核过程与元稳定熔体的物理性质有基本的联系。计划项目的一个主要目的是确定光散射和模拟数据之间巨大差异的来源。为此，首次使用真实空间显微镜来测定低亚稳状态下胶体硬球的结晶成核，其中一些关键的物理性质需要选择性地改变。此外，还计划系统地确定亚稳熔体的结构性质以及亚稳熔体内的晶体成核作为亚稳度的函数。在这些研究中，将使用不同的胶体模型系统。所获得的结果应该允许将熔体的物理性质与晶体成核的物理性质联系起来，从而有可能对结晶过程的基本理解做出重要贡献。

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.