Colloidal Dynamics in Turbid Suspensions

根据其相互作用的范围和强度，胶体颗粒悬浮液可以在不同的时间和长度尺度上发展复杂的动力学以及丰富而迷人的相行为。特别是带电球已经成为化学工业、生物学和医学中遇到的各种电荷稳定的球状胶体的优秀模型。利用传统的同差时域动态光散射（DLS）对这些主要是水基体系的动力学进行研究，往往受到较大浓度下多重散射的开始和结构形成时的时空异质性的限制。存在一些替代技术来应对这些挑战中的一个或两个。例子包括相互关联、回声实验或x射线散射。然而，其中大多数都是相当苛刻的工具。然而，使用超外差多普勒测速技术，一种简单的频域方法可以得到中间散射函数，这是电动力学和流动分析中的一种标准技术。在我们的初步工作中，我们开发了一种有效的集合平均方法，以及该方法的小角度变体的经验，记录后，多次散射校正。在这里，我们建议将这种有前途的技术与传统动态光散射角计设置的多功能性相结合，以研究大范围的散射矢量。使用原型机，我们已经在初步工作中证明了这种方法的概念。现在，博士生需要构建该仪器的改进版本，开发必要的数据处理并实现合适的评估算法。在第一阶段，重点将放在展示其稳健可靠的性能以及绘制其准确度和精度范围上。使用模型系统，工业和生物系统，我们将全面测试机器与时域参考实验，如常规和互相关DLS。在第二阶段，我们将利用之前展示的仪器特征，即多次散射校正，简单的集合平均以及复杂尺度和时间相关动力学的可及性。我们将把新方法应用于我们初步工作中选定的两个例子。在胶体结晶后期阶段的熔体动力学和在低密度带电球玻璃中遇到的弛豫过程都提出了许多有趣的开放性问题。因此，我们的研究也将突出我们的方法的多功能性及其对更广泛的软物质系统的潜在适用性。

Depending on the range and strength of their mutual interactions, suspensions of colloidal particles can develop complex dynamics on different time and length scales as well as a rich and fascinating phase behaviour. Charged spheres in particular have emerged as excellent models for a vast variety of charge-stabilized globular colloids encountered in chemical industry, biology, and medicine. Investigations on the dynamics of these mainly water based systems by conventional homodyne time domain dynamic light scattering (DLS) are often limited by the onset of multiple scattering at larger concentrations and by spatial and temporal heterogeneity upon structure formation. Some alternative techniques to cope with one or both of these challenges exist. Examples include cross-correlation, echo-experiments or X-ray scattering. However, most of these are instrumentally rather demanding. A facile frequency domain approach to the intermediate scattering function is, however, possible usingSuper-Heterodyning Doppler Velocimetry, which is a standard technique in electro-kinetics and flow analysis. In our preliminary work we developed an effective way of ensemble averaging as well as an empirical, post-recording, multiple scattering correction for a small angle variant of this method. Here we propose to combine this promising technique with the versatility of a conventional Dynamic Light Scattering goniometer setup for investigations over a large range of scattering vectors. Using a prototype machine, we have already given proof of concept for this approach in our preliminary work. Now, a PhD student shall construct an improved version of this instrument, develop the necessary data processing and implement suitable evaluation algorithms. In a first stage, focus will be on demonstrating its robust and reliable performance as well as on mapping out its range of accuracy and precision. Using model systems, industrial and biological systems, we will comprehensively test the machine against time domain reference experiments like conventional and cross correlation DLS. In the second stage, we will exploit the instrumental features demonstrated before, i.e. multiple scattering correction, facile ensemble averaging and accessibility of complex scale and time dependent dynamics. We will apply the new approach to two selected examples identified in our preliminary work. Both the melt dynamics during the late stages of colloidal crystallization and the relaxation processes encountered in low density charged sphere glasses pose a number of interesting open questions. Our studies will thereby also highlight the versatility of our approach and its potential applicability for a broader range of Soft Matter systems.