Melting of homogeneously superheated colloidal susensions: processes and their kinetics

到目前为止，熔化过程的现象学被认为是相当好理解的。然而，随着激光脉冲加热技术的出现和计算能力的提高，对强过热固体的研究变得可行。他们的研究结果提出了一些有趣的基本问题的机制和动力学熔化条件下的均匀过热。在这里，我们建议研究的现象融化，并量化其动力学利用胶体模型悬浮液。我们将利用由于胶体特定的时间和长度尺度而产生的优异的光学可达性，并使用最先进的光学方法。除了偏振和布拉格显微镜，我们将采用微分动态显微镜和时间分辨静态光散射。我们将专注于两类静电相互作用的水悬浮液，我们将改变他们的相互作用在一个受控的方式建立实验程序：二元低共熔混合物和热敏颗粒表面活性剂的混合物。在后一种情况下，可以使用表面活性剂的温度依赖性吸附平衡来调节相互作用强度和范围。在我们的初步研究中，我们发现了丰富多样的不同的融化方案，这两个系统类。在第一个资助期内，我们计划对可观察到的过热现象进行全面的概述和分类，并对相应的成核、生长和聚结动力学进行定量测定。稍后，我们还将使用高分辨率显微镜解决熔化的微观机制。我们的研究的长期目标-在均匀过热条件下对熔化采取互补的观点-是对所涉及过程的深入，可能的定量理解的重大贡献。

Up to recently, the phenomenology of the melting process was thought to be quite well understood. However, with the advent of laser pulse heating and increase in computing power, investigations of strongly superheated solids became feasible. Their results raised a number of interesting fundamental questions concerning the mechanisms and the kinetics of melting under conditions of homogeneous superheating. Here, we suggest to study the phenomenolgy of melting and to quantify its kinetics utilizing colloidal model suspensions. We will exploit the excellent optical accessibility due to the colloid specific time and length scales and use state of the art optical methods. In addition to polarization and Bragg microscopy we will employ Differential Dynamic Microskopie and time resolved Static Light Scattering. We will focus on two classes of electrostatically interacting aqueous suspensions, and we will vary their interaction in a controlled way by established experimental procedures: binary eutectic mixtures and thermosensitive particle-surfactant mixtures. In the latter case, the interaction strength and range can be adjusted using the temperature dependent adsorption equilibrium of the surfactants. In our preliminary studies we found a rich variety of different melting scenarios for both system classes. In the first funding period we plan to obtain a comprehensive overview and classification of the observable phenomena in their dependence on superheating as well as a quantitative determination of the corresponding nucleation, growth and coalescence kinetics. Later we will also address the microscopic mechanisms of melting using high resolution microscopy. The long term goal of our studies - taking a complementary view on melting under homogeneously superheated conditions - is a substantial contribution to a deepened, possibly quantitative understanding of the involved processes.