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SYGK: Symposium Rheologische Eigenschaften von Polymersystemen

SYGK 2: Symposium

SYGK 2.2: Vortrag

Montag, 1. März 1999, 16:35–17:00, HS 19

Fourier transform rheology of bulk polymers — •M. Wilhelm, P. Reinheimer, M. Ortseifer, and H.W. Spiess — MPI-Polymer, Postfach 3148, 55021 Mainz, Germany

The application of oscillatory shear strain leads, in the non-linear regime, to the appearance of higher harmonic contributions in the shear stress response. These contributions can be analyzed as spectra in Fourier space with respect to their frequencies, amplitudes and phase angle. In this talk, we present several theoretical and practical aspects for measuring Fourier rheology spectra with high sensitivity. Using the hardware of a conventional rheometer, Fourier rheology spectra with a signal-to-noise ratio of about 18,000:1 for a single acquisition were obtained. This allowed the observation up to the 21st harmonic in case of a polyisobutylen sample. Signal averaging can further increase the sensitivity. The high sensitivity of this Fourier methode can be used in several ways. In the linear regime the phase angle can be measured using shaped waveform excitations to reduce the maximum applied strain. The degree of non-linearity can be described -for single sinusoidal excitations- via the ratio of the third to the fundamental frequency. The measured shear stress is influenced by the folding of a memory related function. Frequency space analysis allows the convenient deconvolution of this memory function.