Critical Point For The Blue-Phase-III-Isotropic Phase Transition In Chiral Liquid Crystals

摘要: The highly chiral compound S,S-4\ensuremath{''}-(methylbutyl)phenyl-4\ensuremath{'}-(methylbutyl) biphenyl carboxylate (S,S-MBBPC) undergoes a continuous supercritical evolution from the isotropic (I) phase to third blue (BPI III). Mixtures of S,S-MBBPC and its racemate have been studied with high-resolution calorimetry capable quantitative latent heat determinations optical activity measurements. Both experiments indicate that first-order BP III--I transition line ends at critical point when mole fraction ${\mathit{X}}_{\mathit{c}}$\ensuremath{\simeq}0.45. Analysis ${\mathit{C}}_{\mathit{p}}$ data for near-critical mixture X=0.45 indicates mean-field behavior instead theoretically predicted Ising fluctuation behavior, which would be analogous liquid-gas simple fluid. It is speculated Ginzburg criterion can explain this since regime may too small experimental observation, as case almost all Smectic-A--Smectic-C transitions. \textcopyright{} 1996 American Physical Society.