Erweiterung des Oszillationsspektrums kommerzieller Rheometer in den Hochfrequenzbereich, an derselben Probe, durch Integration des PRV
FacultiesFakultät für Naturwissenschaften
LicenseStandard (Fassung vom 01.10.2008)
Rheometers are the usual equipment to determine viscoelastic behaviour of materials. One of the various methods used in rheometers is the so called frequency-sweep, which means the application of an oscillating excitation force (stress- or strain-controlled) onto the specimen leads to an oscillating time-delayed deformation signal which is recorded. The shear modulus G* is measured. As a wide frequency range is needed to study all relevant properties of materials during different stages of processing, experimental methods to reach a frequency range as large as possible are needed. For some materials this can be achieved via master-curve techniques (time/temperature shift, TTS) while for other materials specialized instrumentation for real-frequency-spectroscopy is needed. A range of different approachs to this have been developed during last years at the IdM (institute for dynamic materials testing at University of Ulm). As different instruments lead to different preparations and systematic errors it was tried to integrate the PRV (Piezo Rotary Vibrator, frequency range 1Hz- 4kHz), one of this methods into commercial rheometers, to achieved an extended frequency range within a single instrument at same specimen (high-frequency-rheology in rheometer). This thesis introduces into PRV-technique and its optimization, also the advantages resulting from the availability of standard rheometer equipment. Special requirements (e.g. the consideration of moment of inertia of the specimen), resulting from the high frequency measurements are also discussed. Based on that, the successful combination of rheometers and PRVs is described. The experimental efforts (both technical and physical modeling for mathematical correction) needed to merge the two techniques are described and also ways for possible further improvements are pointed out. The PRV insets developed in the course of this work can be set from the opposite side of the rheometer system or into the rheometer system itself. Examples are given to demonstrate the new possibilities of the combined techniques. The special advantage of less mechanical influence of the PRV measurement onto the specimen is pointed out in case of different results originating from the different methods of PRV and rheometer. In a last chapter the integration of dielectric-spectroscopy as an additional measurement modality into the PRV-rheometer-combination is described.
Subject HeadingsViskosimeter [GND]