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

本项目继续进行的目的是了解玻璃形成分子的动态不对称二元混合物在不同时间和长度尺度上的分子动力学，即动态相当不同的伙伴的混合物，每个组分Tg差异很大。事实证明，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，较小的成分保持了高度的迁移率，后者的动力学表现出所谓的内在限制效应。这些效应包括所谓的脆性到强转变，在时间常数的温度依赖性中，特别是对于接近刚性矩阵的小分子，一种特殊的a型玻璃转变，这是先前通过模式耦合理论预测的某些限制情况下的玻璃转变。在项目的后续研究中，将对这种固有约束效应进行研究，并与其他类型的硬约束和软约束效应进行系统比较。研究一方面将基于微乳液体系，这是在项目的第一阶段开发的，为研究软约束提供了机会，也为我们在多孔Vycor基质中过冷二元混合物和液体的光散射提供了经验。因此，在不同类型的硬约束和软约束下研究相同的小分子将成为可能。在实验方法方面，将多散斑相关技术纳入现有的光散射装置中，以便能够有效地利用偏振和去偏振光子相关光谱研究非遍历和部分遍历系统。通过光散射，可以分别监测分子的重定向和浓度波动的衰减。特别是，多散斑技术将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法、宽带介电光谱和准弹性中子散射相结合，以覆盖整个动态范围，并能够解开不同的表面和有限尺寸效应。同时，在不同的时间和长度尺度上研究了浓度波动的衰减，一方面进一步阐明了对混合动力学的影响，另一方面了解了这些波动的温度依赖性。首先用x射线光子相关光谱研究表明，在混合物上部玻璃化跃迁附近部分冻结的浓度波动具有干扰行为，其特征是压缩的相关函数和所谓的相关时间的弹道波矢量依赖。这种不寻常的行为将通过多斑动态光散射进行研究。

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.