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Aggregation-driven, re-entrant isotropic phase in a smectic liquid crystal material

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journal contribution
posted on 16.12.2016, 06:48 authored by Jonathan G. Fernsler, Matthew A. Glaser, Renfan Shao, David A. Coleman, Joseph E. Maclennan, Darren R. Link, Catherine Chang, Kenneth Lanham, David Walba, Cecile Boyer, Joseph A. Zasadzinski, Noel A. Clark

An azobenzene-core chiral mesogen designed for a photoactive ferroelectric liquid crystal system with switchable polarisation displays a highly unusual phase sequence, with a re-entrant, optically isotropic, fluid phase found below smectic phases in mixtures with high enantiomeric purity. The re-entrant isotropic phase is found on the basis of X-ray scattering and freeze-fracture transmission electron microscopy experiments not to be a cubic or other highly ordered phase but instead a translationally disordered liquid. The material also forms a gel under a wide range of concentrations in 50:50 ethanol/chloroform solutions. Ultraviolet/visible and infrared spectroscopy and quantum chemistry calculations suggest that the primary unit in the re-entrant isotropic and gel phases is a dimer composed of molecules crossed by about 90°, which hinders the formation of crystal phases and forms tubules of helical aggregates in the gel phase.

Funding

This work was supported by the National Science Foundation [Grant Numbers DMR-0820579 and DMR-1420736].

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