Anomalous structural response of nematic colloidal platelets subjected to large amplitude stress oscillations

Time-resolved small angle X-ray measurements are used to investigate the dynamic response to nonlinear oscillatory stresses and strains of a nematic dispersion of colloidal gibbsite platelets. We track 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. Under nonlinear oscillatory stress, we observe strong offsets in the rheological response as well as asymmetrical behavior in the microscopic structural response. This offset and asymmetry are connected to the yielding behavior of the platelets. By increasing the stress amplitude, we observed that 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.I. INTRODUCT