Massa Carlo Andrea, Puosi Francesco, Tripodo Antonio, Leporini Dino
Istituto per i Processi Chimico-Fisici-Consiglio Nazionale delle Ricerche (IPCF-CNR), Via G Moruzzi 1, 56124 Pisa, Italy.
Istituto Nazionale di Fisica Nucleare, Largo B. Pontecorvo 3, 56127 Pisa, Italy.
Polymers (Basel). 2021 Apr 19;13(8):1336. doi: 10.3390/polym13081336.
The vibrational dynamics of a model polymer glass is studied by Molecular Dynamics simulations. The focus is on the "soft" monomers with high participation to the lower-frequency vibrational modes contributing to the thermodynamic anomalies of glasses. To better evidence their role, the threshold to qualify monomers as soft is made severe, allowing for the use of systems with limited size. A marked tendency of soft monomers to form quasi-local clusters involving up to 15 monomers is evidenced. Each chain contributes to a cluster up to about three monomers and a single cluster involves a monomer belonging to about 2-3 chains. Clusters with monomers belonging to a single chain are rare. The and character of the clusters is revealed by their fractal dimension df<2. The inertia tensor of the soft clusters evidences their in shape and remarkable correlation of the two largest eigenvalues. Owing to the limited size of the system, finite-size effects, as well as dependence of the results on the adopted polymer length, cannot be ruled out.
通过分子动力学模拟研究了一种模型聚合物玻璃的振动动力学。重点关注对低频振动模式有高度参与度、导致玻璃热力学异常的“软”单体。为了更好地证明它们的作用，将单体被认定为软单体的阈值设定得很严格，从而可以使用尺寸有限的系统。结果表明，软单体有明显的倾向形成包含多达15个单体的准局部簇。每条链对一个簇的贡献最多约三个单体，且单个簇包含约2至3条链中的一个单体。属于单条链的单体组成的簇很少见。这些簇的分形维数df<2，揭示了它们的 和 特征。软簇的惯性张量证明了它们形状上的 以及两个最大特征值之间显著的 相关性。由于系统尺寸有限，不能排除有限尺寸效应以及结果对所采用聚合物长度的依赖性。
