Biomedical Engineering Reference
In-Depth Information
Table 9.17
(
Cont.
)
Compound
R
X
Phase transition behavior
73e
C
11
H
23
SCN
Cr 97 Col
p
172 I
73f
C
11
H
23
BF
4
Cr 66 Col
h
82 I
73g
C
11
H
23
PF
6
Cr 98 Col
h
149 I
74a
C
11
H
23
F
Cr 125 Col
r
128 I
74b
C
11
H
23
Cl
Cr 126 Col
r
128 I
74c
C
11
H
23
Br
Cr 121 I
74d
C
11
H
23
I
Cr 124 Col
r
218 I
74e
C
11
H
23
SCN
Cr 107 Col
r
239 I
74f
C
11
H
23
BF
4
Cr 126 Col
r
168 I
74g
C
11
H
23
PF
6
Cr 242 dec
triphenylene. However, the temperature ranges remain similar. Also, tri-
phenylene compounds exhibited Col
r
phase, while terphenyl compounds
showed Col
h
phase. Variation of R group has not much of an ef ect on the
melting and isotropic point. Change of metal from K
+
to NH
4
+
lowers the
melting point. Both the temperatures vary signii cantly with the change of
counter-anion. Smaller and less polarizable anions like F, Cl and Br reduce
the stability of columnar phase, whereas anions like SCN, BF
4
and I stabi-
lize the mesophase. Surprisingly, PF
6
was found to promote crystallization.
Ef ect of change of size of crown ether has also been observed. For the
[12]crown-4 ether complexes of terphenyl with LiI, enantiotropic Col
h
phase was observed, while for triphenylene with KI showed ordered Col
h
phase. h e KI and CsI complexes of terphenyl with [24]crown-8 ether
showed plastic Col
h,o
phase, while for triphenylene unknown plastic phase
and crystal phases has been observed respectively. On comparison with
[18]crown-6 ether complexes, it was found that phase transition temper-
atures increase with increasing rigidity of the molecular core. However,
mesophases are most stable with [18]crown-6 ether complexes only.
Recently, Aida and his coworkers [110] demonstrated the feasibility of
using ionic DLCs based on triphenylene for orienting single-walled carbon
nanotubes (SWNTs). h ey have shown that triphenylene derivatives are the
best LC dispersants for pristine SWNTs and the dispersed nanotubes give
rise to a homeotropic orientation of the LC columns up to a macroscopic
