The Smectic Q Phase, a Crystal of Twist Grain Boundaries with Smectic Order

Cubic and Other3DThermotropic Liquid Crystal Phases and Quasicrystals

“…The so-called Smectic-Q (SmQ) phases represent a group of 3D chiral structures that are found in chiral calamitic compounds with high twisting power [152,153]. In most cases, the two end chains are identical and are both chiral (compounds 44 and 45, Figure 7.32), but SmQ phases have also been observed in systems where only one end chain is chiral.…”

“…The space groups and lattice parameters of SmQ phases in a series of calamitic compounds were determined by Levelut et al in 1997 [153]. Most phases are tetragonal with space group I422, I4 1 22, or P4 1 22, with one exception of a hexagonal structure, space group P6 2 22 [153]. The unit cell dimensions are similar to the periodicity of the Sm CA phase (the two-layer period), typically around 70Å.…”

“…Such close relation between SmQ phases and the Sm CA has prompted a number of geometrical models on the basis of a complex organization of small Sm CA grains, composed of two layers with alternate molecular tilt [153]. It is envisaged that such complex structures are the result of competition between the tendencies for the chiral molecules to twist and for them to form smectic layers.…”

New chlorine‐substituted liquid crystals possessing frustrated TGBA and SmQ phases

“…Another frustrated phase existing between the antiferroelectric SmC A * and isotropic phases is the smectic Q (SmQ) phase (8,(17)(18)(19)(20). This phase was first reported by Levelut et al (18) and has so far been observed somewhat rarely.…”

“…Location of the chiral moieties in the molecular structure seems to have a significant effect on the appearance of these chiralityinduced frustrated superstructures. The SmQ phase has been reported in materials possessing the identical chiral moiety at both sides of the rigid molecular core (9,(17)(18)(19)(20). X-ray studies of the SmQ phase enable identification of four different structure types all belonging to the class of defect crystals (18).…”