Measurements at Higher Frequencies: Strategies for Increasing Accuracy
Many polymers have the tendency to change their mechanical behavior very strongly with respect to temperature. Limitations by motor inertia are quickly present if frequency sweeps are supposed to be performed at various temperatures, while using the same measurement geometry.
It is well known that polymers have distinct viscoelastic behavior. Sometimes, test methods are required using frequency sweeps at various temperatures. For example:
- determining the crossover point of the storage modulus G' and loss modulus G" functions for calculating the relaxation time of a sample, both depending on the selected measuring temperature
- measuring G' and G" to subsequently determine the master curve, using the method of time-temperature-superposition (TTS).
These two example measurements can be performed easily using a single-drive rheometer. However, when investigating polymers over a large temperature range, their viscoelastic properties can change dramatically, which in turn can hinder the rheological characterization using the same measuring geometry, considering the following two effects.
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