Reconciling calorimetric and kinetic fragilities of glass-forming liquids
Reconciling calorimetric and kinetic fragilities of glass-forming liquids
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DOI：
10.1016/j.jnoncrysol.2016.11.014
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发表时间：
2017-01
影响因子：
3.5
通讯作者：
Qiuju Zheng;J. Mauro;Y. Yue
中科院分区：
文献类型：
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作者：
Qiuju Zheng;J. Mauro;Y. Yue
液体脆性指数（mvis）描述了在玻璃化转变温度（Tg）下玻璃形成液体的粘度随温度变化的速率，这对于理解液体动力学和玻璃化转变本身非常重要。脆性可以直接使用粘度测量来确定。然而，由于测定粘度的各种技术复杂性，需要获得脆性的替代方法。一种简单的方法是基于量热脆性指数（mDSC）的测量，即，在Tg附近的一个小范围内，假想温度（Tf）随加热（冷却）速率的变化率。关键的问题是mDSC如何与vis定量相关。在这里，我们建立了这种关系，通过进行动态和量热测量的一些选定的玻璃组合物覆盖了广泛的液体脆性。结果表明，mDSC与mvis有系统的偏离。该偏差归因于玻璃化转变范围内log（1/qc）~Tg/Tf关系的Arrhenius近似。我们已经开发了一个经验模型来量化的偏差，mviscan很好地预测从DSC在很大范围内的脆弱性。结合高温粘度极限（10-2.93Pa·s），我们仅通过DSC测量就能获得玻璃形成液体的全部粘度曲线。
The liquid fragility index (mvis) describes the rate of viscosity change of a glass-forming liquid with temperature at the glass transition temperature (Tg), which is very important for understanding liquid dynamics and the glass transition itself. Fragility can be directly determined using viscosity measurements. However, due to various technical complications with determining viscosity, alternative methods to obtain fragility are needed. One simple method is based on measurement of the calorimetric fragility index (mDSC), i.e., the changing rate of fictive temperature (Tf) with heating (cooling) rate in a smallTfrange aroundTg. The crucial question is howmDSC is quantitatively related tomvis. Here, we establish this relation by performing both dynamic and calorimetric measurements on some selected glass compositions covering a wide range of liquid fragilities. The results show thatmDSCdeviates systematically frommvis. The deviation is attributed to the Arrhenian approximation of the log(1/qc) ~Tg/Tfrelationship in the glass transition range. We have developed an empirical model to quantify the deviation, by whichmviscan be well predicted frommDSCacross a large range of fragilities. Combined with the high-Tviscosity limit (10–2.93Pa·s), we are able to obtain the entire viscosity curve of a glass-forming liquid by only performing DSC measurements.