Dynamic Light Scattering in Binary Glass Forming Systems -- Concentration Fluctuations, Secondary Processes and Relaxation in Confinement

继续本项目的目的是了解玻璃形成分子的动态不对称二元混合物中不同时间和长度尺度上的分子动力学，即每个组分Tg有很大差异的动态不同伙伴的混合物。结果表明，在一定的温度范围内，这种混合物中的大分子已经动态冻结，较小的组分保持着很高的迁移率，而后者的动力学表现出所谓的本征限制效应。这些效应包括时间常数的温度依赖关系中所谓的从脆弱到强烈的转变，特别是对于接近刚性基质的小分子，这是一种特殊的A型玻璃化转变，这是先前模式耦合理论对某些约束条件下的玻璃化转变所预测的。在项目的继续工作中，研究了这种本征约束效应，并与其他类型的硬约束和软约束的影响进行了系统的比较。这些研究将一方面基于项目第一阶段开发的微乳液系统，并提供研究软约束的机会，还将基于我们在多孔Vycor基质中过冷二元混合物和液体的光散射方面的经验。因此，在不同类型的硬约束和软约束中研究同一小分子是可能的。对于所使用的实验方法，将多散斑相关技术纳入到目前的光散射系统中将是至关重要的，以便能够有效地利用偏振和去偏振光子相关光谱来研究非遍历和部分遍历系统。通过这种方式，可以通过光散射来分别监测分子的重新取向以及浓度波动的衰减。特别是，多散斑技术将被应用于监测非遍历系统中的分子重定向。此外，这些测量将与差示扫描量热、宽带介电光谱和准弹性中子散射相结合，覆盖整个动态范围，并能够解开不同的表面和有限尺寸效应。同时，研究了浓度波动在不同时间尺度和不同长度尺度上的衰减，一方面是为了进一步阐明浓度波动对混合动力学的影响，另一方面是为了了解这些波动的温度相关性。首次用X射线光子相关谱研究表明，在混合物上玻璃化转变附近部分冻结的浓度波动的干扰行为，其特征是压缩的关联函数和所谓的弹道波矢量与关联时间的关系。这种不寻常的行为将用多斑点动态光散射来研究。

The aim of the continuation of the present project is to gain an understanding of the molecular dynamics on different time- and lengthscales in dynamically asymmetric binary mixtures of glass forming molecules, i.e., mixtures of dynamically rather different partners, with a large difference in each components Tg. It turns out that within a certain temperature range, where the large molecules in such a mixture a already dynamically frozen, the smaller component retains a high degree of mobility, and the dynamics of the latter shows so-called intrinsic confinement effects. These effects include a so-called fragile-to-strong transition in the temperature dependence of the time constants and in particular for small molecules close to the rigid matrix a peculiar Type-A glass transition, which was previously predicted by mode-coupling theory for the glass transition in certain confinement situations. In the continuation of the project such intrinsic confinement effects are investigated and systematically compared to effects of other kinds of hard and soft confinement. The investigations will be based on the one hand on the microemulsion systems, which were developed in the first period of the project and provide the opportunity to study soft confinement and also on our experience of light scattering of supercooled binary mixtures and liquids in porous Vycor matrices. Therefore it will be possible to study the same small molecule in different types of hard and soft confinement. Concerning the experimental methods used, it will be crucial to include the multi-speckle correlation technique into the present light scattering setup, in order to be able to efficiently study non-ergodic and partially ergodic systems with polarized and depolarized photon correlation spectroscopy. In this way molecular reorientation as well as the decay of concentration fluctuations can be separately monitored by light scattering. In particular, the multispeckle-technique will be applied to monitor molecular reorientation in non-ergodic systems. In addition, these measurements will be combined with differential scanning calorimetry, broadband dielectric spectroscopy and quasielastic neutron scattering to cover the full dynamic range and be able to disentangle different surface and finite-size effects. At the same time the decay of concentration fluctuations is investigated at different time- and lengthscales, on the one hand to further clarify the influence on the blend dynamics and on the other hand to understand the temperature dependence of these fluctuations. First studies with X-ray photon correlation spectroscopy indicate jamming behavior of partially frozen concentration fluctuations in the vicinity of the mixtures upper glass transition, which is characterized by compressed correlation functions and a so-called ballistic wave-vector dependence of the correlation times. This unusual behavior will be investigated by multispeckle dynamic light scattering.