Fourier-Transform rheology

The application of large amplitude oscillatory shear (LAOS) leads, in the non-linear regime, to a torque response that contains higher mechanical harmonic contributions. These harmonic contributions can be analyzed as spectra in Fourier space with respect to (heir frequencies, amplitudes and phase angle. In this Feature Article, we present first the experimental technique to measure these Fourier rheology spectra. A main emphasize of this feature article is given to a broad variety of applications of this technique to explore the potential use of this mechanical characterization method. The article is organized in the following way: In the First paragraphs the basic ideas and the motivation regarding the ideas of this work are explained. This is important for this technique since these details are often not treated in already published work. This information should facilitate the spread of the technique itself by describing ways to overcome practical problems that may have hindered similar development elsewhere, After this first section several applications of the FT-rheology method are described. Due to the fact that our set up achieves an increased sensitivity by factor 100-1000 compared to former work, many applications in polymer science are anticipated. e.g. the characterization of polymers with different molecular weights, the different responses of polymer dispersions and the identification of the alignment kinetics in block copolymers under shear, just to give some examples. Moreover, FT-rheology will provide valuable information regarding the comparison of the experiment and theoretical models, e.g. constitutive equations, analytical or numerical simulations. At the end an outlook is given towards further development of this technique where for example a new extension of the FT-rheology method into two dimensions is presented, In this experiment a step experiment and oscillatory shear are combined to reach a separation between linear and non-linear response in materials. The outlook section emphasizes that FT- rheology opens up a field with a variety of new possibilities for theoreticians, scientists who develop mechanical characterization methods and personnel responsible for quality control or companies that manufacture rheological devices