DETERMINATION OF A DISCRETE RELAXATION SPECTRUM FROM DYNAMIC EXPERIMENTAL-DATA USING THE PADE-LAPLACE METHOD

The Pade-Laplace method using the Laplace transform and the Pade appro ximants has been used to recover a discrete relaxation spectrum from d ynamic oscillatory data in the molten state for polymers. The method d etects by its own stability the number of modes of the spectrum and ha s been shown to be able to provide spectra with a low number of modes. These spectra are found to be sufficient to obtain an accurate descri ption of the linear viscoelastic behavior in a large frequency range f rom the terminal zone to the plateau zone. Some intrinsic parameters o f the numerical technique have been extensively studied in order to re fine it. Its applicability is shown in the case of polystyrene having monomolecular, bimodal or broad molecular weight distributions. It can easily be implemented on a personal computer and the computing time i s of the order of a few seconds.