(Georgia Institute of Technology, 2010-07)
Park, Min Sang; Yoon, Beom-Jin; Park, Jung Ok; Prasad, Veena; Kumar, Satyendra; Srinivasarao, Mohan
Polarized Raman spectroscopy was used to investigate the development of orientational order and the degree of phase biaxiality in a bent-core mesogenic system. The values of the uniaxial order parameters < P-200 > and < P-400 >, and biaxial order parameters < P-220 >, < P-420 >, and < P-400 >, and their evolution with temperature were determined. The temperature dependence of almost all order parameters reveals a second order transition from the uniaxial to biaxial nematic phase with < P-220 > increasing to similar to 0.22 before a first order transition to the smectic-C phase, upon cooling.
(Georgia Institute of Technology, 2006-10)
Zhou, Jian; Park, Jung Ok; De Luca, Gino; Rey, Alejandro D.; Srinivasarao, Mohan
We study Bloch wall defects formed by quenching nematic thin films from planar anchoring to homeotropic anchoring through a temperature-driven anchoring transition. The director profiles of the walls are directly visualized using fluorescence confocal polarizing microscopy, and shown to agree well with the simulation based on the Frank elasticity theory. A pure twist wall exists if the ratio of sample thickness to surface extrapolation length p is smaller than or close to 1; while a diffuse Bloch wall is obtained if p is much greater than 1.