In-situ Rheo-SAXS study on shear induced alignment of liquid crystal (SCB) in the smectic phase under LAOS

In order to investigate shear induced alignment of lamellar layer of liquid crystal 4-n-octyl-4'-cyanobiphenyl (8CB), a new in-situ Rheo-SAXS, combination of commercial Rheometer (MARS, ThermoFisher scientific) and time-resolved synchrotron small-angle x-ray scattering, was established. For this, specific designed parallel-plate geometry made of transparent Polycarbonate for the upper plate to check the sample loading condition and Vespel for the lower plate was used. A unique special x-ray reflector [diamond, (004)] with d-space 3.51 angstrom reflect x-ray by 90 degrees along the shear gradient direction. Therefore this set-up is unique worldwide in order to measure in-situ 2D-SAXS with normal parallel plate geometry. Large amplitude oscillatory shear (LAOS) at a frequency 10 Hz and a strain amplitude of unity on 8CB with smectic-A at 23 degrees C was applied. After 1 hour of LAOS, the samples were rested during 40 min without shearing. Simultaneously 2D-SAXS pattern were measured. From the experimental results, rheological property and 2D-SAXS pattern, we investigated the mechanism from random lamellar structure towards a shear aligned lamellar structure of 8CB under LAOS. Typically time-resolved synchrotron SAXS can be measured every 2s.