Spatially correlated dynamics in a simulated glass-forming polymer melt: Analysis of clustering phenomena

作     者：Y. Gebremichael T. B. Schrøder F. W. Starr S. C. Glotzer 

作者机构：Center for Theoretical and Computational Materials Science and Polymers Division National Institute of Standards and Technology Gaithersburg Maryland 20899 Chemical Physics Program Institute for Physical Sciences and Technology University of Maryland College Park Maryland 20742 Departments of Chemical Engineering and Materials Science and Engineering University of Michigan Ann Arbor Michigan 48109 

出 版 物：《Physical Review E》 (物理学评论E辑：统计、非线性和软体物理学)

年 卷 期：2001年第64卷第5期

页      面：051503-051503页

核心收录：

学科分类：07[理学] 070203[理学-原子与分子物理] 0702[理学-物理学] 

主　　题：.size distribution clustering intermediate segments glass transition investigate toward glass-forming monomers Polymer Melt Dynamical Heterogeneity spatially heterogeneous mean cluster correlated dynamics mobile subset peak time 

摘      要：In recent years, experimental and computational studies have demonstrated that the dynamics of glass-forming liquids are spatially heterogeneous, exhibiting regions of temporarily enhanced or diminished mobility. Here we present a detailed analysis of dynamical heterogeneity in a simulated “bead-spring model of a low-molecular-weight polymer melt. We investigate the transient nature and size distribution of clusters of “mobile chain segments (monomers) as the polymer melt is cooled toward its glass transition. We also explore the dependence of this clustering on the way in which the mobile subset is defined. We show that the mean cluster size is time dependent with a peak at intermediate time, and that the mean cluster size at the peak time grows with decreasing temperature T. We show that for each T a particular fraction of particles maximizes the mean cluster size at some characteristic time, and this fraction depends on T. The growing size of the clusters demonstrates the growing range of correlated motion, previously reported for this same system [C. Beneman et al. Nature (London) 399, 246 (1999)]. The distribution of cluster sizes approaches a power law near the mode-coupling temperature, similar to behavior reported for a simulated binary mixture and a dense colloidal suspension, but with a different exponent. We calculate the correlation length of the clusters, and show that it exhibits similar temperature- and time-dependent behavior as the mean cluster size, with a maximum at intermediate time. We show that the characteristic time of the maximum cluster size follows the scaling predicted by mode-coupling theory (MCT) for the β time scale, revealing a possible connection between spatially heterogeneous dynamics and MCT.