Abstract
High-resolution calorimetry has been used to determine the heat capacity and latent heat associated with phase transitions in the homologous series of chiral liquid crystals nF2BTFOIM7 (3-fluoro-4(1-methylheptyloxy)4'-(4-alkoxy-2,3-difluorobenzoyloxy)tolane). These compounds exhibit smectic-C* (SmC*), twist-grain-boundary (TGBA for n = 10, TGBC for n = ii, 12) and cholesteric (N*) phases. All the phase transitions are first order with small to moderate latent heats. There is a large rounded excess heat capacity peak in the N* phase that is consistent with the predicted appearance of short-range TGB order (chiral line liquid character). This is analogous to the development of an Abrikosov flux vortex liquid in type-II superconductors. Both the n = 11 and 12 homologs exhibit two closely spaced transitions in the region where a single TGBC N* transition was expected. This suggests the existence of two thermodynamically distinct TGBC phases.
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