Cooperativity of dynamics in supercooled polymeric materials and its temperature dependence predicted from a surface controlled model
Cooperativity of dynamics in supercooled polymeric materials and its temperature dependence predicted from a surface controlled model
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DOI：
10.1016/j.eurpolymj.2018.01.003
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发表时间：
2018-02
影响因子：
6
通讯作者：
Akinori Sato;Takashi Sasaki
中科院分区：
文献类型：
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作者：
Akinori Sato;Takashi Sasaki
协同性与链段动力学脆性之间的关系是阐明过冷聚合物液体粘性减速的关键问题。基于最近提出的协同重排区（CRR）呈弦状的假设，对p-取代聚苯乙烯（PS衍生物）和聚甲基丙烯酸酯（PMAEs）的实验结果进行了重新分析.分析表明，这两种聚合物体系的协同性和脆弱性之间存在明显的正相关关系。为了研究协同性的温度依赖性，我们提出了一个简单的模型，其中CRR的大小由其表面积控制（表面控制CRR模型：SCC模型）。基于该模型的分析表明，对于许多聚合物来说，CRR呈非致密形状，具有高表面积与体积比。最小CRR的构型熵也从量热法的SCC模型的基础上进行评估，它被揭示依赖于段弛豫时间非常弱，与典型的非聚合物玻璃形成。
Relation between cooperativity and fragility of segmental dynamics is a crucial issue in elucidating the viscous slowdown of supercooled polymer liquids. The experimental results previously reported forp-substituted polystyrenes (PS derivatives) and poly(methacrylic acid ester)s (PMAEs) are reanalyzed based on a cooperative string model that was recently proposed on the assumption that the cooperatively rearranging region (CRR) takes a string shape. The analysis shows clear positive correlations between the cooperativity and fragility for both the polymer systems. To investigate the temperature dependence of the cooperativity, we proposed a simple model where the size of the CRR is controlled by its surface area (surface-controlled CRR model: SCC model). The analysis based on this model suggests that for many of the polymers, the CRR takes a non-compact shape with high surface-to-volume ratio. The configurational entropy of the smallest CRR is also evaluated from calorimetry based on the SCC model, and it is revealed to depend on the segmental relaxation time very weakly compared with that for typical non-polymeric glass-formers.