Simultaneous use of rheological and optical techniques leads to a better understanding of the dependencies between the microstructure and the mechanical properties of complex fluids and polymeric materials in particular. Different optical methods such as small angle light scattering, microscopy (polarized, fluorescence, confocal), spectroscopy (NIR, IR, Raman), birefringence and dichroism have been employed.<br/>A rheo polarized imaging techniques (SIPLI - shear induced polarization light imaging) which measures the local stresses through the detection of the birefringence and Raman spectroscopy are discussed in more detail. Employing a parallel-plate geometry with SIPLI the whole measuring plate is observed and the birefringence can be displayed over the full range of shear rates within one single experiment. For directly relating the changes in rheological behavior to chemical changes or phase transition Raman spectroscopy can be used in situ with rheology.<br/>A rheometer platform based on a combined motor transducer (CMT) rheometer equipped with an electrically commutated synchronous motor on the upper side facilitates the use of a second motor on the bottom side. The second motor could either be a rotational or a linear drive. By using a rotational drive, the device is turned into a separate motor transducer (SMT) rheometer by using one motor as drive and the second as a torque transducer. Additionally, it can operate in a counter rotational mode, where both motors rotate in opposite directions and thus enabling the creation of a stagnation line in the sample at which it is sheared but not moved from its position for rheo-microscopy. A SMT mode has some advantages in sensitivity under certain measurement conditions and allows the use of special tools such as for example a cone-partitioned-plate (CPP), which enables measurements even if edge fracture would hinder them in standard geometries. Combining the upper rotational motor with a linear drive in the bottom permits new testing capabilities. By solely using the linear drive Dynamic Mechanical Analysis (DMA) testing on more solid like samples with various geometries like tension, three-point bending, cantilever, or in compression is possible. Using a geometry for solid bars DMA in tension by the linear drive and DMA in torsion by using the upper rotational drive are possible on the same specimen, thus allowing to extract not only the DMA parameters but also the Poisson ratio.

Advanced polymer rheology based on rheo-optical tools and a dual motor device

ACS Spring 2022

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