Abstract
The alignment behavior of the triphenylene compounds possessing fluoroalkylated side chains was investigated for the hexagonal columnar (Col_h) mesophase by polarizing optical microscopy and the polyimide-, cetyltrimethylammonium bromide (CTAB)-, and Indium-SnO_2 (ITO) -coated glass substrates were used in this work. It was found that 2, 3, 6, 7, 10, 11-hexakis (1H, 1H, 2H, 2H, 3H, 3H-perfluoroheptyloxy)- and 2, 3, 6, 7, 10, 11-hexakis- (1H, 1H, 2H, 2H, 3H, 3H-perfluorononyloxy) -triphenylenes (F4 and F6, respectively) exhibit a spontaneous homeotropic alignment on these substrates, in contrast to the non-uniformity of spontaneous alignment of Col_h phase in the corresponding hydrocarbon mesogens. On the other hand, it was also found that 4, 4, 4-trifluorobutyloxy, 4, 4, 5, 5, 5-pentafluoropentyloxy and 4, 4, 5, 5, 6, 6, 6-heptafluorohexyloxy (F1, F2 and F3, respectively) derivatives do not show such a spontaneous homeotropic alignment on these substrates. These results indicate that the spontaneous homeotropic alignment of the Col_h phase could be easily attained by the introduction of an appropriate number and length of the fluoromethylene chains in the peripheral parts of discogens.
