Phase Transitions in Freely Suspended Smectic Droplets. Cotton-Mouton Technique, Architecture of Droplets and Formation of Nematoids

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Abstract
Phase transitions of aqueous suspensions of droplets of smectogens have been studied using the collective Cotton-Mouton (CM) technique. Two compounds were examined: NPOOB and 8OCB. A statistical model (previously developed for suspensions of nematogens) has been adapted to describe the collective CM effect in these systems. It was found that both the phase transitions and the changes of architecture within the droplets cause distinct changes in the CM effect. An attempt was made to investigate suspensions of theliquid crystalline germs created in the isotropic melts of nematic and smectic mesogens mixed with a chiral additive. In such mixtures, nematoids (the liquid crystal analogues of the whiskers of crystalline solids) are formed. It is usually found that nematoids arise as an extension of the tail of a monopole droplet or grow from a focal conic multipole droplet but “free” nematoids (without droplets at their ends) can also occur. The aspect ratio of nematoids varies with the composition, ranging from about 3 to 3,000. When cooled, nematoids rapidly condense to droplets with the formation of a spiral or double spiral often occurring at an intermediate stage. The architecture of germs in N-S-chiral melts is discussed.