Dresden 2014 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 43: Glasses and Glass Transition (joint session with DY/DF) I
CPP 43.1: Invited Talk
Thursday, April 3, 2014, 11:45–12:15, ZEU 114
Dynamics and thermodynamics of glassy polymers below the glass transition temperature — •Daniele Cangialosi — Paseo M Lardizabal 5, 20080 San Sebastian, Spain
Glass-forming systems constitute an important class of materials. Among different aspects, the dramatic slowing down of the dynamics when decreasing temperature and the possible connection between such slowing down and the thermodynamics of the glass-former have been intensively studied. It has been speculated that mere extrapolation of the dynamics and thermodynamics to temperatures below the glass transition temperature (Tg) produces a singularity at a finite temperature, with divergent relaxation time and vanishing configurational entropy. Here the dynamics and thermodynamics are studied at temperatures as low as Tg − 40 K by performing enthalpy recovery experiments on glassy polymers for times up to 107-108 seconds. We find a single stage recovery behavior for temperatures larger than about Tg − 10 K. A double stage recovery is observed for T < Tg − 10 K. The enthalpy recovered after the two-stage decay equals that extrapolated from the melt, whereas partial enthalpy recovery occurs in the first decay. From the analysis of the time to reach each equilibrium it is found that the equilibration time corresponding to the first stage recovery exhibits relatively low activation energy, whereas the second one exhibits activation energy similar to that of the polymer segmental relaxation. These results indicate a complex scenario of the dynamics and thermodynamics below Tg with multiple equilibration steps and leave open the question the finite temperature singularity.