Dynamics of polycarbonate far below the glass transition temperature:: A positron annihilation lifetime study -: art. no. 134206

被引:38
作者
Cangialosi, D
Wübbenhorst, M
Schut, H
van Veen, A
Picken, SJ
机构
[1] Delft Univ Technol, Dept Polymer Mat & Engn, NL-2628 BL Delft, Netherlands
[2] Dutch Polymer Inst, NL-5600 AX Eindhoven, Netherlands
[3] Delft Univ Technol, Interfac Reactor Inst, NL-2629 JB Delft, Netherlands
关键词
D O I
10.1103/PhysRevB.69.134206
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
In this study, we have extended the knowledge of the dynamics of polycarbonate (PC) far below T-g by means of positron annihilation lifetime spectroscopy (PALS), which is able to detect the isothermal relaxation of the free volume after rejuvenation above T-g. The free volume relaxation patterns at different temperatures below T-g were modeled according to a phenomenological model presented by Struik to obtain the equilibrium relaxation times of the process at each aging temperature. The dynamics of supercooled liquids above the glass transition temperature (T-g) is usually described by the Williams-Landel-Ferry (WLF) or Vogel-Fulcher-Tammann (VFT) equation. Recently, deviations from this behavior were found below T-g. In contrast, an Arrhenius-type temperature dependence was found. Our results suggest that, far below T-g, two possible scenarios can hold: (a) the relaxation process of PC is dominated by the beta process, though the fast modes of the alpha process still manifest even at the lowest investigated temperature; (b) an Arrhenius-type process, deriving from the coupling of few beta events, drives aging far below T-g. Finally, the aging process was related to a diffusion mechanism and a coupling parameter was introduced as a measure of the efficiency of the beta process in producing appreciable changes in the density. The magnitude of the coupling parameter suggests a weak coupling between the beta relaxation and the physical aging process.
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页码:134206 / 1
页数:9
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