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Relaxation mapping analysis with an hyperbolic heating rate
Published online by Cambridge University Press: 11 February 2011
Abstract
Thermally stimulated discharge currents (TSDC) together with the Relaxation Map Analysis (RMA) method is a convenient method to study relaxation processes in complex materials. In the RMA technique, one performs repeated TSDC runs while selecting polarization states through the use of a fixed polarization time schedule and a sucessively higher polarization temperature. Each peak has an associated polarization strength and a pair of activation parameters which can be the Gibbs free activation energy and the activation entropy. In the present paper we propose a different approach to RMA. It consists of a global heating of the sample in an hyperbolic manner to determine the activation parameters as a function of temperature. This determination is done by first selecting a value for the activation entropy for each temperature and then calculating the implied activation enthalpy or Gibbs free energy.
We have reasoned that normal relaxation processes usually proceed with a null or close to zero activation entropy and that only relaxations associated to the glass transitionand/or cooperative phenomena involve large values of the activation entropy. In those cases and based on the curvature of the TSDC curve one can select a minimum activation entropy value which will fit the TSDC curve at a particular temperature. Using this data one determines the polarization strength associated to each pair of activation parameters. Results for the TSDC relaxation parameters spectra of a liquid crystal polymer will be presented together with comparisons between the thermal sampling method and the proposed method.
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- Copyright © Materials Research Society 2003