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| Hauptseite > Publikationsdatenbank > Anomalous rheological response of nematic platelets studied by 3D Rheo-SAXS and XPCS |
| Hauptseite > Publikationsdatenbank > Anomalous rheological response of nematic platelets studied by 3D Rheo-SAXS and XPCS |
| Conference Presentation (Plenary/Keynote) | FZJ-2020-05333 |
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2020
Abstract: Dispersions of colloidal Gibbsite platelets in the nematic phase show intriguing anomalous behaviour when sheared, due to the strong wall anchoring of such systems. When subjecting this system to Large Amplitude Oscillatory Shear, an elastic response is observed at low strain amplitudes, but time-resolved rheo-SAXS experiments show that the structural response is symmetry broken. At high strain amplitude a yielding transition between elastic and plastic deformation is observed during a period, accompanied by a flipping of the director. When applying Large Amplitude Oscillatory Stress, the system displays a strong offsets in the rheological response as well as asymmetrical behavior in the microscopic structural response. With increasing stress amplitude the offset of the rheological response diminishes and the microscopic response becomes more symmetric. However, this strongly depends on the frequency of the stress input, and hence the time necessary for the system to yield. Here we tracked the full 3D rotational motion of the director by employing plate-plate and concentric cylinder Couette geometries as well as a vertical X-ray beam. Finally, we show that the response throughout the gap is strongly inhomogeneous, as well in structure as in velocity. To this end we performed XPCS measurements in ``tangential" scattering geometry in a Couette cell to obtain velocity profiles.
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