Principles and Application of Fourier-Transform Rheology in the Identification of Polymer Alloys

Today, almost all polymer researchers use rheological methods to identify the microstructure of various polymer systems. One of the most popular and widely used methods is the small amplitude oscillatory shear (SAOS) test. SAOS provides a set of valuable information about the microstructure of polymeric materials. Various materials in this test are examined only in the linear viscoelastic region (LVR). However, polymer melts (raw, alloy, composite, etc.) are exposed to a much higher shear rate in processing methods. Therefore, the study of the non-linear behavior of polymers is of particular importance. Fourier transform rheology (FT rheology) is one of the most advanced methods for identifying the microstructure of polymers. The use of large amplitude oscillatory shear (LAOS), which leads to departure from the LVR, is the basis of the method. The stress response to this large deformation has the basic harmonies and involves higher odd harmonies that complicate the response form. In this method, the Fourier transform technique is used to convert a complex response in the time domain to a simple response in the frequency domain. The mentioned response contains valuable information about the microstructure of materials, which is impossible to extract (with this high accuracy) from the output responses in the LVR.