Anomalous component dynamics of a binary mixture of associating glass-forming liquids.
Anomalous component dynamics of a binary mixture of associating glass-forming liquids.
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DOI：
10.1021/jp1101362
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发表时间：
2011-02
期刊：
影响因子：
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通讯作者：
Li-Min Wang;Yongjun Tian;Riping Liu;K. Ngai
中科院分区：
文献类型：
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作者：
Li-Min Wang;Yongjun Tian;Riping Liu;K. Ngai
丙二醇（PG）与2-乙基己胺（EHA）二元混合物的高T(g)组分PG随着低T(g)组分EHA浓度的增加而发生的动态变化，与其他缔合和非缔合二元混合物的变化趋势截然不同，甚至相反。例如，加入EHA后，PG组分的脆性指数m增大，耦合参数n增大，而在EHA的0.5摩尔分数下，PG组分的T(g)没有变化。从不同组分的PG组分的宽带介电光谱特征来看，这些异常是由于EHA组分的存在增强了高t (g) PG组分的初级弛豫中的分子间耦合。这种增强可以追溯到这样一个事实，即整齐的EHA比整齐的PG具有更大的分子间偶联，尽管前者的T(g)低于后者。随着EHA浓度的增加，PG组分的分子间偶联增强，当EHA的摩尔分数增加到0.75时，PG组分的JG β-弛豫与α-弛豫分离。而纯PG的JG β-弛豫与α-弛豫太接近，无法分辨。PG在混合物中的异常动力学是所有玻璃化转变理论和模型都难以解释的。对异常动力学的物理起源的洞察导致了耦合模型框架的合理化。
The binary mixtures of propylene glycol (PG) with 2-ethylhexylamine (EHA) show changes of the dynamics of the higher-T(g) component PG on increasing the concentration of the lower T(g) component EHA very different or even opposite in trend from those found in other associating and nonassociating binary mixtures. For example, the fragility index m increases and the coupling parameter n of the PG component increases on adding EHA, while T(g) of the PG component does not change up to 0.5 molar fraction of EHA. From the features present in the broadband dielectric spectra of the PG component at different compositions, the anomalies are identified to originate from the enhancement of intermolecular coupling in the primary relaxation of the higher-T(g) PG component by the presence of the EHA component. The enhancement can be traced to the fact that neat EHA has larger intermolecular coupling than neat PG, despite the former having a lower T(g) than the latter. The enhancement of intermolecular coupling of the PG component increases on increasing the concentration of EHA in the mixture, as evidenced by the appearance of the JG β-relaxation of the PG component well separated from the α-relaxation when the molar fraction of EHA has been increased to 0.75. In contrast, the JG β-relaxation of neat PG is too close to the α-relaxation and cannot be resolved. The anomalous dynamics of PG in the mixtures is challenging to all theories and models of glass transition to explain. The insight gained on the physical origin of the anomalous dynamics leads to a rationalization in the framework of the coupling model.