Spacer length dependence of TGBC* and SmA phases in cholesteryl and dihydrocholesteryl-containing trimer liquid crystals

A.T.M. Marcelis, M. Giesbers, A. Koudijs

Research output: Contribution to journalArticleAcademicpeer-review

15 Citations (Scopus)

Abstract

Two series of trimer liquid crystals were investigated that contain a biphenylyl central group and two cholesteryl or dihydrocholesteryl terminal mesogenic groups. Only compounds with even spacers were investigated. The dihydrocholesteryl-containing trimers show a triply intercalated smectic A (SmA) phase when the spacer lengths are greater than 8, whereas the cholesteryl-containing trimers exhibit this triply intercalated SmA phase when the spacer lengths are more than 6. With shorter spacers, a twist grain boundary C* (TGBC*) phase was found. This is revealed by the formation of a typical dotted square grid pattern upon cooling from the chiral nematic (N*) phase in the planar texture. The dots are spaced by a distance of about 1.5-1.8 µm. Upon cooling from the N* phase in the focal conic texture a striped pattern is observed with the same spacing. X-ray diffraction revealed a repeat distance for the TGBC* phase that corresponds with a monolayer ordering. The results show that the weaker interaction between the dihydrocholesteryl groups compared with cholesteryl groups or longer spacers destabilize the monolayer TGBC* phase.
Original languageEnglish
Pages (from-to)811-817
JournalLiquid Crystals
Volume34
Issue number7
DOIs
Publication statusPublished - 2007

Keywords

  • twist grain-boundary
  • smectic-c-phase
  • dimesogenic compounds
  • mesomorphic behavior
  • optical-properties
  • mesogenic units
  • terminal group
  • dimers
  • moiety
  • series

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