Dynamic Heterogeneities in Binary Glass-Forming Systems
Dynamic Heterogeneities in Binary Glass-Forming Systems
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DOI：
10.1007/978-3-319-72706-6_6
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
D. Bock;T. Körber;F. Mohamed;B. Pötzschner;E. A. Rössler
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文献类型：
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作者：
D. Bock;T. Körber;F. Mohamed;B. Pötzschner;E. A. Rössler
首先概述了纯玻璃成形体中主（α）和次（β）弛豫的主要结果，这些结果是由介电谱和核磁共振（NMR）光谱以及光散射编纂的，贡献涉及阐明二元玻璃成形体中的组分动力学。动态不对称混合物，其组成部分的高tgcontrast的焦点。除聚合物外，特殊合成的非聚合物玻璃形成物被认为是高tgcomponent，并与低tgsimple液体混合。混合物中的高热分量表现出与纯玻璃形成物相似的弛豫特征，而低热分量表现出明显更快的动力学和明显的动态非均质性，即相关时间g （lnτ）分布极其广泛，这可能导致准对数相关函数。确定了两个具有重要浓度依赖性的玻璃化转变温度。二维交换核磁共振证实了这种动态非均质性本质上是短暂的。因此，在本质上刚性的高tgmatrix中观察到低tgadditive的类液体（各向同性）重定向以及其分布（lnτ）内的交换。结果表明，在非对称二元玻璃成形体中，（本征）约束效应也可能控制动力学。我们还研究了低热添加剂引入的混合玻璃中的β-过程。对于几乎没有时间常数变化的所有浓度，它都被重新发现。核磁共振鉴定出β弛豫与纯玻璃的弛豫相似。角位移低于±10°的空间高度受限运动包含所有分子。在核磁共振中观察到非常相似的光谱特征。显然，（小）添加剂分子“奴役”大分子，以执行共同的受阻重定向。在最低的添加剂浓度下，人们发现β过程开始瓦解的迹象。我们认为β-过程是一个合作过程。
Starting with an overview of major results of the main (α) and secondary (β) relaxation in neat glass formers as compiled by dielectric and nuclear magnetic resonance (NMR) spectroscopy as well as by light scattering, the contribution deals with elucidating the component dynamics in binary glass formers. Dynamically asymmetric mixtures with high-Tgcontrast of their components are in focus. In addition to polymers, specially synthesized non-polymeric glass formers are considered as high-Tgcomponent and mixed with a low-Tgsimple liquid. While the high-Tgcomponent in the mixtures shows relaxation features similar to that of neat glass formers, the low-Tgcomponent displays significantly faster dynamics and pronounced dynamic heterogeneities, i.e., an extremely broad distribution of correlation timesG(lnτ), which may lead to quasi-logarithmic correlation functions. Two glass transition temperatures with non-trivial concentration dependences are identified. The dynamic heterogeneities are transient in nature as proven by 2D exchange NMR . Thus, liquid-like (isotropic) reorientation of the low-Tgadditive as well as exchange within its distributionG(lnτ) is observed in an essentially rigid high-Tgmatrix. The results show similarity with those collected for glass formers in confining geometries, suggesting that in asymmetric binary glass formers (intrinsic) confinement effects may control the dynamics either. We also investigate the β-process in the mixed glasses introduced by the low-Tgadditive. It is rediscovered for all concentrations with virtually unchanged time constants. NMR identifies the β-relaxations as being similar to those of neat glasses. A spatially highly restricted motion with an angular displacement below ±10° encompasses all molecules. Very similar spectral features are observed for the high-Tgcomponent in NMR. Apparently, the (small) additive molecules “enslave” the large molecules to perform a common hindered reorientation. At lowest additive concentrations, one finds indications that the β-process starts to disintegrate. We conclude that the β-process is a cooperative process.