Fragiadakis D, Roland CM. Dynamic correlations and heterogeneity in the primary and secondary relaxations of a model molecular liquid.
PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014;
89:052304. [PMID:
25353797 DOI:
10.1103/physreve.89.052304]
[Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2014] [Indexed: 06/04/2023]
Abstract
Molecular dynamics simulations were carried out on a series of Lennard-Jones binary mixtures of rigid, asymmetric, dumbbell-shaped molecules. Below an onset temperature, the rotational and translational dynamics split into the slow structural α relaxation and a higher-frequency Johari-Goldstein β relaxation. Both processes are dynamically heterogeneous, having broad distributions of relaxation times. However, only the α relaxation shows strong dynamic correlations; correlations at the β time scale are weak, in particular for molecules having shorter bonds. Despite the close connection between the two processes, we find no correlation between the α and β relaxation times of individual molecules; that is, a molecule exhibiting slow β motion does not necessarily undergo slow α dynamics and likewise for fast molecules. However, the single-molecule α relaxation times do correlate with both the α and β relaxation strengths.
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