Chemistry Reference
In-Depth Information
NO
2
CH
3
CH
3
CH
3
O
CH
3
(R)-
CH
3
Si
O
Si
O
Si
(
CH
2
)
6
O
CO
O
CHC
5
H
11
*
CH
3
CH
3
CH
3
isotropic-56°C-Sm
A
*-25°C-Sm
C
*
Figure 6.21
Chemical structure, molecular shape, and phase sequence of a liquid
crystal 4-[3
-((R)-1-methylhexyloxy) phenyl] phenyl 4-(6-heptylmethyltrisiloxy-
hexyloxy) benzoate (TSiKN65). Sm
A
*, chiral smectic A; Sm
C
*, chiral smectic C.
-nitro-4
′
′
is possible to discuss the orientation of the local structure for the
molecular long axis.
The molecular structure of the ferroelectric liquid crystal was inves-
tigated (Figure 6.21) [42]. The orientational order of phenyl rings at
the core part (1604 cm
− 1
) was measured in the ferroelectric state
induced by applying external electric fi eld. The obtained apparent
order parameters are 0.48 for
app
. These values
are extremely small compared with the typical values for Sm
A
or Sm
C
liquid crystals (cf. Table 6.1). Here, we should be aware that the longest
principal axis of the Raman tensor possibly tilts somehow with respect
to the molecular long axis;
〈
P
2
〉
app
and 0.12 for
〈
P
4
〉
〈
P
2
〉
app
and
〈
P
4
〉
app
may generally differ from
〈
P
2
〉
and
〈
P
4
〉
even in an orthogonal Sm
A
phase. Therefore,
〈
P
2
〉
app
and
app
depend not only on the molecular thermal fl uctuations but also
on the angle
〈
P
4
〉
0
between the longest principal axis of the Raman tensor
and the molecular long axis. The tilting angle of the core part was
estimated as 28.5 ° from Equation 6.47, assuming that the typical
values of
β
are 0.8 and 0.6, respectively. The large tilting
angle of the core part can be deduced from the polarized Raman
analysis (Figure 6.22 ).
〈
P
2
〉
and
〈
P
4
〉
6.7 RECENT DEVELOPMENTS OF THE RAMAN TECHNIQUE
FOR LIQUID CRYSTAL STUDY
Spectroscopic investigations not only support the development of LCD
but also elucidate the physics of liquid crystals, e.g. the molecular inter-
action between liquid crystal molecules and between the polymer and
liquid crystal, and the mechanism of the reorientation of liquid crystal
molecules induced by phase transitions or external fi eld.
Polymer-dispersed liquid crystals are mainly developed as materials
for display applications. The mechanism of the molecular orientation
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