Double helical defects in smectic A and smectic A* phases

Abstract

Double helical (DH and DH*) domains, defects of the smectic A (SmA) phase, have for the first time been studied in the smectic A* (SmA*) phase, composed of chiral molecules. Both left- and right-handed DH*s are found in SmA*s, but not in equal numbers. The majority of the DH*s in the two left-handed cholesterics studied are left-handed, whereas in the SmA phase of non-chiral molecules the DHs are left- and right-handed in equal numbers. DHs and DH*s, which are topologically screw dislocations of giant Burgers vectors, appear to be significantly distorted with respect to a geometrically ideal model. It has been shown that imperfections in the DH*s and DHs are covered by a combination of three types of elementary distortions. The relation between the pitch in DH* and DH and temperature is discussed.

Keywords:

• chiral smectic A
• defects
• double helices
• screw dislocations

Acknowledgements

The study was supported by the Ministry of Education and Science of Ukraine, as Project 0109U001062. YuN is grateful to the Université de Picardie Jules Verne for hospitality and financial support resulting from appointment as Invited Professor in 2007 and 2009. This is IPGP contribution # 2609 (MK).

Notes

1. For example, the DH domains observed in the B7 phase [5] are ideal inside the cylinder (perfect isometry, the layers being parallel to the central ruled helicoid) but the outer part of the cylinder is distorted to the point at which it is in the isotropic liquid state.