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Home  >  Journal list  >  Polymer Journal  >  Vol.24  No.1 (1992)  >  pp.15-24

Polymer Journal
<<Previous article Vol.24  No.1 (1992)   pp.15 - 24 Next article>>

Analysis of the Relaxation and Retardation Spectra Obtained from the Double-Log Representation of the Viscoelastic Functions

F. Povolo1)2) and Élida B. Hermida1)
1) Dto. de Física, Fac. de Ciencias Exactas y Naturales, U.B.A.
2) Dto. de Materiales, Comisión Nacional de Energía Atómica


ABSTRACT:  Relaxation or retardation distribution functions are sometimes used to determine the molecular models of the polymeric structure of a linear viscoelastic material. These spectra are usually calculated from the double-log representation of any mechanical property, using approximation methods. In this paper it is shown that the double-log plots distort the viscoelastic behavior, leading to spectra that do not describe the real mechanical response. To solve this problem, a normalized representation of the measurements is proposed and its improvements are discussed in detail. Particularly, the retardation spectrum determined from the normalized dynamic compliance of polyisobutylene is taken as an example, showing some inconsistencies in the model determined from the double-log representation. Finally, even with the normalized representation, the spectra derived from the master curves do not always provide a good fitting of these curves. Hence, it is pointed out that the analysis of individual curves measured over several decades of time or frequency leads to a better determination of the real distribution function of characteristic times.


Keyword:
Viscoelastic Functions/ Double-Log Representation/ Relaxation and Retardation Spectra/ Master Curve

Published online: April 04, 2005
© Copyright, 2005 by The Society of Polymer Science, Japan

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