University of Minnesota
School of Physics & Astronomy


Investigating Orientational Order of Liquid Crystals


from Science Highlight, a publication of Brookhaven National Laboratory.

Authors: S. Jaradat, P. Brimicombe, C. Southern, S. Siemianowski, E. DiMasi, M. Osipov, R. Pindak, H. F. Gleeson, Z.Q. Liu, B.K. McCoy, S.T. Wang, W. Caliebe, P. Barois, P.Fernandes, H.T. Nguyen, C.S. Hsu, and C.C. Huang

Orientational order enables technological applications for liquid crystals as positional order does for crystals. Three groups, headed by Cheng-Cher Huang from the University of Minnesota, Helen Gleeson from The University of Manchester, and Philippe Barois from Bordeaux University, collaborated with NSLS scientists Ron Pindak and Suntao Wang to use the technique of resonant x-ray scattering for measuring orientational order in layered liquid crystal phases with periodicities from nanometers to micrometers. The layered phases were comprised of molecules tilted with respect to the layer normal, which were either chiral, rod-shaped molecules, or banana-shaped molecules. Because of the chirality or banana-shape of the molecules, the tilted, layered, liquid-crystal phases lack a mirror symmetry, which allows the existence of an in-plane polarization
perpendicular to the tilt-plane of the molecules and along the bow in the banana-shaped molecules like an arrow in a bow. Depending on how the direction of the in-plane polarization varies between layers, the phases can be ferro-, ferri-, heli-, or antiferroelectric and an applied electric field can induce changes in orientation or, if sufficiently high, changes in phase. Electric-field-induced reorientation of the large optical
anisotropy of the molecules has been utilized in applications from high-resolution camera viewfinders to large-area monitors. These three research groups each made significant discoveries regarding the behavior of these intriguing and technologically important phases.