ISSN:
0098-1273
Keywords:
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The behavior of the multiparameter KAHR model (put forward by Kovacs, Aklonis, Hutchinson, and Ramos) has been investigated using a single-box retardation spectrum to describe the kinetics of volume and enthalpy recovery of glasses in three-step thermal cycles involving colling, isothermal annealing, and subsequent reheating. It has been shown that during the heating stage, the system may display up to three peaks in the expansion coefficient and the specific heat. The shifts of the peak temperatures Tp with respect to each of the four experimental variables Yi defining the thermal history are analyzed systematically in terms of a set of reduced variables, scaled by two of the material constants of the system. These shifts, from which the various partial derivatives (∂Tp/∂Yi)j≠i are estimated, are determined for five values of another material parameter x, which characterizes the relative contributions (O ≤ x ≤ 1) of temperature and structure to the retardation times. the results show that the upper peak is always small and is insensitive to the characteristics of the spectrum and to the value of x, while the relevant peak temperature depens only slightly on the cooling and heating rates. On the Other hand, the magnitude and the shifts of the main peak depend on all the experimental variables and the material constants in a rather complex manner. It is shown, however, that in limiting situations, involving fast heating of well-stabilized glasses, the shifts of the relevant peak temperature T̂all reduce to a linear function of x-1. since this relationship is rather insensitive to the shape of the spectrum, the experimental determination of any one of the nonzero partial derivatives of T̂ provides a simple means for an independent estimate of the value of the important material constant x. Finally, the shifts of the upper and main peaks relative to each other will be analyzed in terms of the pertinent experimental variables and compared with actual data reported in the literature for polymer glasses.
Additional Material:
15 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1984.180220909
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