Fig. 2
From: Heliconical smectic phases formed by achiral molecules
Phase behaviour. a Phase diagram for the achiral CB6OIBeOn series with n = 4–10, the filled points correspond to a 50–50 wt.% mixture of homologues n = 6 and 7. b Smectic layer spacing, d, vs. temperature for CB6OIBeOn compounds with n = 7–10. The dependence, d(T), for n = 7 and 8 suggests a transition from an orthogonal to a tilted phase. The highlighted area is the heliconical smectic CTB phase. In the inset is the enlarged fragment of d vs. T for homologue n = 8, which clearly shows the SmA-SmAb phase transition. c Optical textures of the uniaxial SmA, biaxial SmAb, helical SmCTB and HexI phases, observed in an homeotropic cell, between crossed polarizers, for homologue CB6OIBeO8. A glass bead is visible in the picture to mark the same area of the presented textures. Note that the SmCTB phase is uniaxial, which excludes a simple synclinic or anticlinic tilted structure. d Schematic drawing of the proposed model for SmCTB phase structure in which dimeric molecules form a short-pitch helix, p stands for pitch length. The dotted vertical lines denote smectic layer interfaces, spaced by d
