Colloidal Dynamics in Turbid Suspensions

根据胶体颗粒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。尤其是带电球体，已经成为化学工业、生物和医学中遇到的各种电荷稳定的球状胶体的优秀模型。用传统的零差时间域动态光散射(DLS)研究这些主要是水基体系的动力学时，往往受到较大浓度的多次散射开始时的限制，以及结构形成时的时空不均一性的限制。存在一些替代技术来应对这些挑战中的一个或两个。例如互相关、回波实验或X射线散射。然而，其中大多数都是相当苛刻的工具要求。然而，一种简便的计算中间散射函数的频域方法是可以使用超差多普勒测速技术，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系综平均方法，以及对该方法的一个小角度变体的经验、记录后多次散射校正。在这里，我们建议将这一有前途的技术与传统动态光散射测角仪的多功能性结合起来，用于在大范围的散射矢量上进行研究。使用样机，我们已经在初步工作中给出了这种方法的概念证明。现在，一名博士生将构建该工具的改进版本，开发必要的数据处理并实施适当的评估算法。在第一阶段，重点将是展示其稳健和可靠的性能，以及制定其准确度和精确度范围。使用模型系统、工业和生物系统，我们将针对传统和互相关DLS等时域参考实验对机器进行全面测试。在第二阶段，我们将利用前面演示的工具特性，即多次散射校正、简单的系综平均以及复杂尺度和依赖于时间的动力学的可访问性。我们将把新的方法应用于我们的初步工作中确定的两个选定的例子。胶体结晶后期的熔体动力学和低密度荷电球体玻璃中遇到的弛豫过程都提出了一些有趣的开放问题。因此，我们的研究也将突出我们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.