Temperature behavior of the Kohlrausch exponent for a series of vinylic polymers modelled by an all-atomistic approach
Département de Chimie, Université de Sherbrooke, 2500 boul. de l’Université, Sherbrooke, Québec, Canada
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Revised: 24 May 2011
Accepted: 8 July 2011
Published online: 22 September 2011
The Kohlrausch-Williams-Watt (KWW) function, or stretched exponential function, is usually employed to reveal the time dependence of the polymer backbone relaxation process, the so-called α relaxation, at different temperatures. In order to gain insight into polymer dynamics at temperatures higher than the glass transition temperature T g , the behavior of the Kohlrausch exponent, which is a component of the KWW function, is studied for a series of vinylic polymers, using an all-atomistic simulation approach. Our data show very good agreement with published experimental results and can be described by existing phenomenological models. The Kohlrausch exponent exhibits a linear dependence with temperature until it reaches a constant value of 0.44, at 1.26T g , revealing the existence of two regimes. These results suggest that, as the temperature increases, the dynamics progressively change until it reaches a plateau. The non-exponential character then describes subdiffusive motion characteristic of polymer melts.
© EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg, 2011