Correlating fragility and heterogeneous dynamics in polystyrene through single molecule studies
Correlating fragility and heterogeneous dynamics in polystyrene through single molecule studies
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DOI：
10.1063/1.5114905
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发表时间：
2019-08-28
影响因子：
4.4
通讯作者：
Kaufman, Laura J.
中科院分区：
文献类型：
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作者：
Manz, Alyssa S.;Aly, Mariam;Kaufman, Laura J.
聚合物的许多宏观性质取决于它们的分子量，其中一个值得注意的例子是玻璃化转变温度：具有较高分子量的聚合物通常具有比它们的较低分子量聚合物和低聚物对应物更高的玻璃化转变温度。接近其玻璃化转变温度的聚合物系统也表现出有趣的性质，表现出高（和分子量依赖）的脆弱性和强有力的证据动态异质性。虽然研究已经详细说明了分子量和脆性之间的相关性，但缺乏明确详细说明分子量和非均匀动力学程度之间相关性的研究。在这项研究中，我们使用单分子转动测量来研究分子量对聚苯乙烯在其玻璃化转变温度附近的非均匀性程度的影响。为此，两种类型的荧光探针被嵌入在膜组成的聚苯乙烯范围从0.6至1364.0千克摩尔（-1）。我们发现聚苯乙烯的分子量，脆性，和动态异质性程度之间的相关性报告的单分子拉伸指数，但没有发现这些数量和时间尺度与动态交换之间的明确相关性。由AIP Publishing授权出版。
Many macroscopic properties of polymers depend on their molecular weight, with one notable example being glass transition temperature: polymers with higher molecular weights typically have higher glass transition temperatures than their lower molecular weight polymeric and oligomeric counterparts. Polymeric systems close to their glass transition temperatures also exhibit interesting properties, showing both high (and molecular weight dependent) fragility and strong evidence of dynamic heterogeneity. While studies have detailed the correlations between molecular weight and fragility, studies clearly detailing correlations between molecular weight and degree of heterogeneous dynamics are lacking. In this study, we use single molecule rotational measurements to investigate the impact of molecular weight on polystyrene's degree of heterogeneity near its glass transition temperature. To this end, two types of fluorescent probes are embedded in films composed of polystyrene ranging from 0.6 to 1364.0 kg mol(-1). We find correlation between polystyrene molecular weight, fragility, and degree of dynamic heterogeneity as reported by single molecule stretching exponents but do not find clear correlation between these quantities and time scales associated with dynamic exchange. Published under license by AIP Publishing.