Influence of chain stiffness on the dynamical heterogeneity and fragility of polymer melts.
Influence of chain stiffness on the dynamical heterogeneity and fragility of polymer melts.
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DOI：
10.1063/1.5052153
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发表时间：
2018-12
期刊：
影响因子：
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通讯作者：
Deng Pan;Zhao‐Yan Sun
中科院分区：
文献类型：
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作者：
Deng Pan;Zhao‐Yan Sun
公认较硬的聚合物具有较高的玻璃化转变温度。然而，在接近玻璃化转变点时，链刚度对慢动力学和动力学不均匀性的影响仍然没有得到很好的理解。在这项工作中，我们研究的影响链刚度的动态不均匀性和脆性的过冷聚合物熔体的分子动力学模拟。通过改变弯曲强度来调节链的刚度，并研究了聚合物链段的扩散和松弛。我们发现，重标扩散系数和结构弛豫时间之间的幂律关系不随链刚度的变化而变化，表明具有不同链刚度的聚合物熔体的玻璃形成行为的相似性。用非高斯参数和动力学磁化率表征了系统的动力学不均匀性，用弦长分析了类弦合作运动。研究发现，非高斯参数和动态磁化率表征了动力学不均匀性的不同方面。虽然降低温度和增加弯曲强度都导致动力学变慢和动力学不均匀性增加，但温度和弯曲强度之间没有简单的叠加。我们的工作可能为不同链刚度的聚合物的玻璃化转变行为提供新的线索。
It is well accepted that stiffer polymers have higher glass transition temperatures. However, the influence of chain stiffness on the slow dynamics and dynamical heterogeneity when approaching the glass transition point is still not well understood. In this work, we investigate the influence of chain stiffness on the dynamic heterogeneity and fragility of supercooled polymer melts by using molecular dynamics simulation. The chain stiffness is tuned by varying the bending strength, and the diffusion and relaxation of polymer segments are studied. We find that the power law relation between the rescaled diffusion coefficient and the structural relaxation time does not change with changing chain stiffness, indicating similarities of glass-forming behavior of polymer melts with different chain stiffness. The dynamical heterogeneities are characterized by the non-Gaussian parameter and dynamic susceptibility, and the string-like cooperative motion is analyzed by the string-length. It is found that the non-Gaussian parameter and dynamic susceptibility characterize a different aspect of dynamical heterogeneities. Though both decreasing temperature and increasing bending strength lead to slower dynamics and growing dynamical heterogeneities, there is no simple superposition between temperature and bending strength. Our work may shed new light on the glass transition behavior of polymers with different chain stiffness.