“Magneto-optical and Imaging Studies of Chromonic and Thermotropic Liquid Crystals”

 

This talk aims to provide insight for three experimental questions. First, 
the pretransitional behavior of lyotropic chromonic liquid crystals is 
investigated in order to gain further insight into the aggregation mechanism, 
aggregate cross section and presence of induced optical effects. Since the flat 
shape of chromonic molecules lends itself to the formation of linear aggregates, 
this particular class of liquid crystal holds potential for understanding both 
molecular interactions and supramolecular assembly, as essential differences in 
their molecular structure contribute to differences in the organization of the 
aggregates, the character of the aggregation, and aggregate packing. The second 
part of this talk explores the possibility of a biaxial nematic phase (Nb). The 
geometry of the liquid crystal mesogen plays a key role and, as a result, it is 
widely believed that the banana-shaped liquid crystals will have an Nb phase. 
However, contradicting reports on different bent-core materials have not given 
a conclusive answer to whether this phase actually exists in a bent-core material, 
despite the numerous experimental techniques used to probe these materials. The 
last part of this talk examines thermal fluctuations in calamitic and bent-core 
liquid crystals in their nematic phase, using dynamic imaging analysis. Dynamic 
image analysis is a relatively new technique whereby one makes a measurement in 
direct space of nematic phase fluctuations, rather than in inverse space as is 
done with traditional light scattering experiments. These measurements are done 
using a polarizing microscope, heat stage and fast CCD camera. The advantage of 
this technique is that it may achieve smaller values of q, making it a 
complementary technique to dynamic light scattering, where large values 
of q are easily studied.