The smectic Q phase, a crystal of twist grain boundaries with smectic order

A structural analysis of the so-called smectic Q mesophase was performed on nine different chiral compounds. Not less than four different structures were observed, and they all belong to the crystal of defects class. The defects of the liquid crystalline organization are stacked in three dimensional crystalline lattices of tetragonal or hexagonal symmetries, and the lattice constants are in the range of 65-130 Angstrom. In all cases but one, the constitutive defects are twist grain boundaries in a smectic structure with twist angles of pi/2 or pi/3. The fourth phase organization has to be compared to that of blue phase and it can be considered as a stack of double twist clusters.