Confinement effects on mesoscopic structures of macromolecules

Abstract

We present the first experimental results demonstrating a novel approach to con-trolling the size as well as the spatial patterning of defect domains in a smectic liquid crystal by geometric confinement in surface modified microchannels. By confining the liquid crystal 8CB (4``-octyl-4-cyanobiphenyl) in micron sized rectangular channels with controlled surface polarity, we were able to generate defect domains that are not only nearly uniform in size but also arranged in quasi-two-dimensionally ordered patterns. Atomic force microscopy measurements revealed that the defects have a toroidal topology, which we argue is dictated by the boundary conditions imposed by the walls of the microchannel. We show that the defects can be considered as colloidal objects, which interact with each other to form ordered patterns. This method opens the possibility to exploit the unique optical and rheological properties associated with LC defects to making new materials. For example, the control of the shape, size and spatial arrangement of the defects at the mesoscale suggests applications in patterning, templating, and when extended to lyotropic liquid crystals, a process leading to uniform size spherical particles for chemical encapsulation and delivery. On the other hand, we present the direct imaging of the internal structure of the toroidal defects in SmA liquid crystal droplet, by laser scanning confocal fluorescence microscopy (LSCFM). The consideration on the fluorescence anisotropy of rod molecule, based on the boundary conditions, gives us the understanding in the molecular orientation of liquid crystals in the defects, and therefore, we successfully distinguish the toroidal topology from the onion like spherulite. Additionally, we studied on the confinement effect of the undulation instability of thermotropic liquid crystal 8CB near the transition temperature of nematicsmectic phase and it``s transformation into focal conic toroidal defects. We present the strong corr...