Fouriertransform rheology (FT-Rheology)
The basic method for determination of mechanical properties of polymers is rheology using oscillating excitation. This method is the foundation of many research areas of the group of Prof. Wilhelm. In analogy to the non-linear optics, the amplitude and the frequency of the exitation can be raised steadily, finally resulting in an non-linear answer of the material. The FT-Rheology is a special, high sensitive extension of normal oscillating Rheology to the non-linear regime that has been developed in our group.
Actual working fields in the research strand FT-Rheology are on the one side further development of the method itself, e.g. improvements in resolution via intelligent data recording (oversampling). On the other hand, we also work on different evaluation techniques of the non-linear response functions. Recently, we presented a new non-linearity parameter Q that is extremely sensitive for the topology of polymers, especially for long-chain branching. Another aspect of this strand is the comparison of non-linear information with numerical simulation, e.g. constitutive equations for polymer meltsA. FT-Rheology offers an experimental approach for the non-linearity effects predicted by theory and can be used for comparisons or for the adjustment of nonlinearity parameters, e.g. in the Giesekus-model. A further point belonging in this research strand is the work about flow anomalies in polymer processing.
A basic idea of our work is the knowledge transfer with other research groups interested in non-linear rheology. Up to now, approximately 30 copies of the FT-Rheology (Distribution of FT-Rheology worldwide) were installed all over the world. The latest cooperations on the topic of FT-Rheology were with the MIT (Prof. G. McKinley), Caltech ( Prof. J. Kornfield) and Harvard( Prof. Weitz). In addition, to the cooperation with research group, we could achieve a commercial equipment for FT-Rheology in cooperation with TA-Instruments.