Temperature dependence of local segmental motion in polystyrene and its variation with molecular weight

Dielectric measurements are reported for the α-relaxation in polystyrene (PS) of varying molecular weights. Although the segmental relaxation dispersion was essentially invariant to Mw, the Tg-normalized temperature dependence (fragility) increases systematically with molecular weight. The latter re...

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Bibliographic Details
Published in:The Journal of chemical physics 2003-07, Vol.119 (3), p.1838-1842
Main Authors: Roland, C. M., Casalini, R.
Format: Article
Language:English
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Summary:Dielectric measurements are reported for the α-relaxation in polystyrene (PS) of varying molecular weights. Although the segmental relaxation dispersion was essentially invariant to Mw, the Tg-normalized temperature dependence (fragility) increases systematically with molecular weight. The latter result corroborates dynamic mechanical and light scattering studies, but is at odds with the reported (T−Tg) superpositioning of the shift factors for the recoverable creep compliance of PS. The failure of the dielectric relaxations time to superimpose when expressed as a function of T−Tg is consistent with the analysis of equation of state data for PS. We find that volume is not the dominant control variable, and in fact, temperature exerts a stronger influence on the relaxation times.
ISSN:0021-9606
1089-7690
DOI:10.1063/1.1581850