Rheological and Optical Behavior of Suspensions of Shape-Changing Liquid Crystal Drops

We report on experiments that explore macroscopic rheological and optical behavior of ensembles of micron-size drops containing liquid crystal (LC) oligomers; these drops exhibit shape transformations [1]. The drops contain polydisperse nematic liquid crystal oligomers (NLCOs) composed of RM82 and are suspended in water. With temperature variation, the drops evolve into nematic structures, ranging from spheres to branched filamentous networks. These morphologies can be produced reversibly, and if desired, can be converted into liquid crystal elastomers (LCEs) by UV curing. In the present work, we anticipate changes in drop hydrodynamics, and therefore changes in the whole suspension rheological behavior, with heating and cooling. We study this rheological response in a cone-and-plate rheometer during steady-state shear as a function of temperature. Using an optical microscope with a Bertrand lens, we also measure the change in transmittance of light scattered by the drop suspensions at various temperatures. Through this characterization of the suspensions, we hope to create a reversible optical and rheological switch.