A comparative study on the dynamic heterogeneity of supercooled polymers under nanoconfinement
A comparative study on the dynamic heterogeneity of supercooled polymers under nanoconfinement
复制标题
纳米约束下过冷聚合物动态非均质性的比较研究
DOI：
10.1039/c9cp02550b
复制
发表时间：
2019
影响因子：
3.3
通讯作者：
Lu Zhong-Yuan
中科院分区：
文献类型：
--
作者：
Li Shu-Jia;Qian Hu-Jun;Lu Zhong-Yuan
动态不均匀性（DH）是玻璃化转变现象的普遍性质。在这项工作中，我们进行了比较分析的DH纯聚合物和聚合物/纳米粒子复合材料系统在薄膜和散装状态，通过分子动力学模拟。我们发现，由于自由表面的存在，动态梯度和更快的平均动态是两个主导因素，从纳米约束效应，这影响了膜系统中的DH的不同部分。动态梯度是由离移动的表面不同距离处的动力学差异引起的，这引起了膜中位移分布与高斯分布的较大偏差。同时，描述合作运动（动态相关）的区域大小的最大串大小也会受到动态梯度的影响，尽管这种影响比对位移分布的影响要弱得多。另一方面，反映动力学或DH的时间部分的时间波动，非高斯参数和字符串大小的特征峰值时间，以及描述动态交换性质的持续时间和交换时间之间的比率，主要受平均较快的动力学的影响。我们的研究结果表明，测量不同的属性（动态分布，动态相关性或动态交换）的重点放在不同的时间和空间部分的DH。有必要使用这些属性的组合测量，以给出一个完整的图片DH在nanoconfinition环境。
Dynamic heterogeneity (DH) is a universal property of glass transition phenomena. In this work, we perform a comparative analysis of DH for pure polymer and polymer/nanoparticle composite systems in both film and bulk states via molecular dynamics simulations. We find that the dynamic gradient and the faster average dynamics due to the presence of a free surface are two leading factors, resulting from a nanoconfinement effect, which influence different parts of DH in a film system. The dynamic gradient results from differences in dynamics at different distances from the mobile surface, which induces a large deviation from the Gaussian distribution for the displacement distribution in the film. At the same time, the maximum string size which describes the region size for cooperative motion (dynamic correlation) can also be influenced by the dynamic gradient, although this influence is much weaker than that on the displacement distribution. On the other hand, reflecting temporal fluctuations of dynamics or temporal parts of DH, characteristic peak times of the non-Gaussian parameter and string size, and the ratio between persistent times and exchange times which describe the dynamic exchange properties, are mainly influenced by the faster dynamics on average. Our results demonstrate that measuring different properties (dynamic distribution, dynamic correlation or dynamic exchange) place an emphasis on distinct temporal and spatial parts of DH. It is necessary to use combinational measurements of these properties to give a complete picture of DH in nanoconfinement environments.