title: Quantifying changes in the low-frequency dynamics of amorphous polymers by 2D correlation mechanical spectroscopy.
abstract: The longer segmental dynamics of sub-Rouse modes in polystyrene with different molecular weights has been investigated by 2D correlation mechanical spectroscopy. The sub-Rouse modes were first separated from the α relaxation and Rouse modes, and their dynamics exhibits a similar change at the same temperature, T(B) ≈ 1.2T(g), as the α relaxation. The relaxation time of sub-Rouse modes at T(B) is independent of molecular weight and has a value of about 0.1 s, indicating that solely the time scale of the relaxation determines the change in dynamics of sub-Rouse modes. According to the coupling model, the change is caused by a strong increase in intermolecular cooperativity. The present work provides direct evidence for the intermolecular coupled nature of the sub-Rouse modes and demonstrates that the properties of the sub-Rouse modes resemble those of α relaxation, which could provide a new perspective for understanding the glass transition of polymers.
authors.affiliation: Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, P.O. Box 1129, Hefei 230031, PR China. xbwu@issp.ac.cn
authors.forename: Xuebang
authors.initials: X
authors.lastname: Wu
authors.forename: Huaguang
authors.initials: H
authors.lastname: Wang
authors.forename: Zhengang
authors.initials: Z
authors.lastname: Zhu
authors.forename: C S
authors.initials: CS
authors.lastname: Liu