Effect of Polymers on Crystallization in Glass-Forming Molecular Liquids: Equal Suppression of Nucleation and Growth and Master Curve for Prediction
Effect of Polymers on Crystallization in Glass-Forming Molecular Liquids: Equal Suppression of Nucleation and Growth and Master Curve for Prediction
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DOI：
10.1021/acs.cgd.9b01095
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发表时间：
2020-01-01
影响因子：
3.8
通讯作者：
Yu, Lian
中科院分区：
文献类型：
--
作者：
Yao, Xin;Huang, Chengbin;Yu, Lian
晶体成核在过冷液体和玻璃的稳定性中起着关键作用，并且通常通过添加聚合物来控制。溶解的聚合物改变成核的热力学和动力学，但目前对这些影响的理解是有限的。晶体成核速率已在两种分子液体D-山梨糖醇和D-阿拉伯糖醇中测量，所述分子液体含有不同浓度（0-15重量%）和分子量（对于二聚体为224 g/mol，最高达2 Mg/mol）的聚乙烯吡咯烷酮（PVP）。我们观察到一个显着的抑制效果PVP晶体成核。在成核速率的峰值温度附近（类似于玻璃化转变温度以上20 K），10重量% PVP可以使成核减慢约1个数量级，并且该效果随着聚合物浓度和分子量呈指数增加。值得注意的是，3聚合物对成核速率的影响与晶体生长速率的影响几乎相同，使得两种速率的比率在给定温度下几乎恒定，与聚合物浓度和分子量无关。这种“主曲线”行为可以用来预测多组分体系中的成核速率，从更容易测量的生长速率。它认为，在这些粘性液体中的成核和生长都是流动性有限的，并且聚合物溶质的功能主要是作为流动性改性剂，抑制成核和生长到类似的程度。
Crystal nucleation plays a critical role in the stability of supercooled liquids and glasses and is often controlled through addition of polymers. A dissolved polymer alters both the thermodynamics and the kinetics of nucleation, but the current understanding of these effects is limited. The rate of crystal nucleation has been measured in two molecular liquids, D-sorbitol and D-arabitol, containing polyvinylpyrrolidone (PVP) at different concentrations (0-15 wt %) and molecular weights (224 g/mol for the dimer up to 2 Mg/mol). We observe a significant inhibitory effect of PVP on crystal nucleation. Near the peak temperature for the nucleation rate (similar to 20K above the glass transition temperature), 10 wt % PVP can slow down nucleation by approximately 1 order of magnitude, and the effect increases with polymer concentration exponentially and with molecular weight. Remarkably, the 3 polymer effect on the nucleation rate is nearly the same as that on the crystal growth rate so that the ratio of the two rates is nearly constant at a given temperature independent of polymer concentration and molecular weight. This "master curve" behavior can be used to predict nucleation rates in multicomponent systems from more easily measured growth rates. It argues that nucleation and growth in these viscous liquids are both mobility-limited and that a polymer solute functions mainly as a mobility modifier, suppressing nucleation and growth to a similar degree.