F. Hardouin et al., Influence of the molecular length on the occurrence of incommensurate low ordered smectic phases for non-symmetric dimesogenic compounds, LIQ CRYST, 26(4), 1999, pp. 589-599
Systematic physical chemistry studies are in progress concerning the occurr
ence of incommensurate low ordered smectic phases (S-ic)dagger in non-symme
tric dimesogens with molecular parameters varying from those of the standar
d compound KI-5(4). In the present study, the selected molecules possess th
e same cholesteryl unit and the same spacer length, but the terminal chain
of the aromatic mesogenic part is varied. Up to a critical molecular length
, a competition between two incommensurate lengths is observed and the dime
sogenic compounds respond to the frustration connected to this competition
with the formation either of an incommensurate phase S-ic or of a two dimen
sional modulated phase. For longer dimesogens, a commensurate lock-in of th
e two characteristic lengths systematically occurs.