Dynamically asymmetric binary glass formers studied by dielectric and NMR spectroscopy
Dynamically asymmetric binary glass formers studied by dielectric and NMR spectroscopy
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DOI：
10.1140/epje/i2019-11909-5
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发表时间：
2019-11-01
影响因子：
1.8
通讯作者：
Roessler, E. A.
中科院分区：
文献类型：
--
作者：
Koerber, Th;Minikejew, R.;Roessler, E. A.
我们研究了非对称二元玻璃形成剂的组分动力学。对高Tg组分间三甲苯基磷酸酯和喹哪啶与低Tg组分甲苯混合物的介电谱进行了研究，发现其宽端谱不能用Kohlrausch或Cole-Davidson（CD）函数描述。相反，我们应用一个广义CD函数，它允许控制独立于其高频侧翼的磁化率的宽度。随着甲苯浓度的增加，光谱显示出频率-温度叠加的普遍加宽和失效。这是证实了受激回波实验，显示了探测的取向相关函数的拉伸增加。类似于T-g的定义，我们考虑“等动力点”。对于每个组件，不同的，但线性浓度依赖性的1/T-iso被揭示，表明不同的时间尺度。定性地，我们没有发现本发明的混合物的T-g-对比度为63- 89 K相比，具有较大的T-g-对比度（Δ T-g > 170 K）的显着差异：而高-T-g组件显示类似于那些净玻璃形成者的弛豫特征，然而，与“非典型”弱弛豫加宽，更快的低-T-g组件显示出明显的动态不均匀性。这是支持通过仔细检查NMR弛豫数据的几个混合物以前调查作为浓度的函数。一个普遍的演变的动力学的高-T-g以及低-T-g组件的建议与高Δ T-g的混合物。
We investigate the component dynamics in asymmetric binary glass formers. Focusing on the dielectric spectra of the high-T-g components m-tricresyl phosphate and quinaldine mixed with toluene as low-T-g component, the broadend spectra cannot be described by Kohlrausch or Cole-Davidson (CD) functions. Instead, we apply a generalized CD function which allows to control the width of the susceptibility independently of its high-frequency flank. The spectra show a common broadening and failure of the frequency-temperature superposition with increasing toluene concentration. This is confirmed by stimulated echo experiments showing an increased stretching of the probed orientational correlation function. In analogy to the definition of T-g, we consider "isodynamic points". For each component, a different but linear concentration dependence of 1/T-iso is revealed, indicating different time scales. Qualitativly, we do not find significant differences for the present mixtures with T-g-contrasts of 63-89K compared to those with larger T-g-contrast (Delta T-g > 170 K): Whereas the high-T-g component shows relaxation features similar to those of neat glass formers, yet, with "atypical" weak relaxation broadening, the faster low-T-g component displays pronounced dynamic heterogeneities. This is supported by scrutinizing NMR relaxation data of several mixtures investigated previously as a function of concentration. A universal evolution of the dynamics of the high-T-g as well as the low-T-g component is suggested for mixtures with high Delta T-g.