Abstract
In this article, the effect of an incomplete frequency range on relaxation spectra calculated with the new spline-based method (Stadler and Bailly, Rheol Acta 48(1):33–49, 2009) presented before is discussed. The range, in which the spectrum can be determined, is limited by the range of the input data, but not directly by the inverse frequency. The actual limits depend on the range of input data. Depending on the shape of the spectrum the relaxation spectrum can be determined from the input data in a range up to three decades larger than the input data. This can be explained by the influence of the modes outside the inverse frequency range. For this purpose, a new concept, the relevance factor analysis, was introduced, which allows for a determination of the limits of spectrum calculation. The characteristic relaxation times are discussed in comparison for to the calculation of \(J_e^{\rm 0}\) and η 0 from the spectrum.
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Notes
Another reason for the limitation of TTS for extending the frequency regime is the accessible temperature range, which is limited by crystallization, glass transition, and degradation of the polymer.
The contributions were calculated by calculating the ratio of G ′(ω) and G ″(ω) from the whole range to G ′(ω) and G ″(ω) calculated from the reduced relaxation time range. The contributions given in the text refer to the maximum value of this ratio.
The calculation of the relevance factors is very much straightforward, but requires a lot of computations for complex spectra (and, therefore, anybody should be warned to use arrays with significantly more than 1,000 frequencies by 1,000 relaxation times for numerical reasons). The Matlab®-script written by the author for that purpose can be obtained upon request. To use it, a full Matlab®-installation is required.
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Acknowledgements
The author wants to acknowledge the financial aid from Communauté Française de Belgique. FJS would like to thank Prof. Dr. Christian Bailly (Université catholique de Louvain (UCL), Belgium), Prof. em. Dr. F. R. Schwarzl and Dr. J. Kaschta (University Erlangen-Nürnberg), and Prof. H. H. Winter (University of Massachusetts, Amherst) for stimulating discussions about this topic.
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Stadler, F.J. Effect of incomplete datasets on the calculation of continuous relaxation spectra from dynamic-mechanical data. Rheol Acta 49, 1041–1057 (2010). https://doi.org/10.1007/s00397-010-0479-0
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DOI: https://doi.org/10.1007/s00397-010-0479-0