Development of heterogeneity near the glass transition: phenyl-ring-flip motions in polystyrene

B. Vorselaars, A.V. Lyulin, M.A.J. Michels

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37 Citations (Scopus)

Abstract

Mol. dynamics simulations are employed to study the phenyl-ring flip in polystyrene, thought to be the mol. origin of the gamma -relaxation. The results show that upon cooling the system toward the glass transition the motion of the Ph ring becomes more heterogeneous, which seems to result from a distribution of local energy barriers in combination with slower transitions between states with these local energy barriers. The growing of the heterogeneity affects the detn. of the effective energy barrier. In particular, the "static" energy barrier (as detd. from the distribution of the orientation of the Ph ring with respect to the backbone) is found to be different from the "dynamic" energy barrier, as detd. from the temp. dependence of some relaxation time (i.e., the activation energy). However, below the glass transition temp. it appears that the two methods render the same value for the height of the energy barrier, although the time scales differ approx. by a const. factor. It is shown that another relaxation time can be detd. to characterize the ring-flip process, which seems not to be affected by the growth of heterogeneity and which closely follows the "static" energy barrier. The effective barrier as detd. in this way by the simulations is in fair agreement with exptl. values for the gamma -relaxation. [on SciFinder (R)]
Original languageEnglish
Pages (from-to)6001-6011
JournalMacromolecules
Volume40
Issue number16
DOIs
Publication statusPublished - 2007

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