Alignment behaviour of the discotic nematic phase of 2,3,6,7,10,11-hexa (4-n-octyloxybenzoyloxy) triphenylene on polyimide and cetyltrimethylammoniumbromide coated substrates
H. Monobe et al., Alignment behaviour of the discotic nematic phase of 2,3,6,7,10,11-hexa (4-n-octyloxybenzoyloxy) triphenylene on polyimide and cetyltrimethylammoniumbromide coated substrates, LIQ CRYST, 28(8), 2001, pp. 1253-1258
The orientational behaviour of the nematic discotic phase of 2,3,6,7,10,11-
hexa(4-n-octyloxybenzoyloxy) triphenylene ( C8OBT) on substrates coated wit
h a polyimide or cetyltrimethylammonium bromide ( CTAB) was investigated by
polarizing optical microscopy. The averaged order parameters and direction
s of the triphenylene core and the carbonyl groups of C8OBT were evaluated
by an infrared dichroic method. The discotic nematic (N-D) phase of C8OBT e
xhibits a homeotropic alignment on a polyimide film, a typical nematic schl
ieren texture on a glass substrate, and a tilted or planar homogeneous alig
nment on a CTAB-coated substrate. The order parameter of the triphenylene c
ore is higher on a polyimide film (S = 0.6) than on a CTAB-coated substrate
(S = 0.2), whereas that of the carbonyl groups remains roughly constant at
0.2 to 0.3 independent of the substrate for the N-D phase.