Chemistry Reference
In-Depth Information
Table 6.3. The pitch, magnetic threshold, magnetic susceptibility anisotropy
and twist constant of PBLG(Mn = 310,000) at three kinds of solvents. (From
DuPre, 1982.)
Solvent
P
0
(
H
c
(kG)
K
22
/χ
a
χ
a
(10
−
8
esu/cm
3
)
K
22
(10
−
12
N)
m)
µ
dioxane
30
5.06
9.6
0.64 + 0.07
0.62
trichloromethane
42
6.87
33.7
0.64 + 0.09
2.1
dichloromethane
80
5.23
72.3
0.74 + 0.05
5.4
Table 6.4. Data of
K
22
/χ
a
of PBLG (Mn = 150,000)
solutions. (From Parthasarathy
et al
., 1988.)
Solvent
K
22
/χ
a
cyclohexanone
4.7
dioxane
9.5
dioxane/60% trifluoro-acetyl fluoride
14.4
pyridine
20.0
nitrobenzene
18.1
metatoly
22.0
The results are listed in Table 6.4, the molecular weight of PBLG being
150,000, and the equivalent molecular length is 1000 A.
The twist elastic constant of PBLG is a function of the concentration
in solution, seen from Figure 6.6(a), and of the temperature, shown in
Figure 6.6(b). It is demonstrated that
K
22
is approximately proportional
to the concentration in solution as the theory predicts and decreases as
temperature increases and thus the order parameter decreases.
Three kinds of Frederiks transitions can be used to measure the three
elastic constants of nematic polymers. The magnetic threshold fields
H
ci
are functions of
K
ii
(
i
=1
,
2
,
3) respectively,
K
ii
χ
a
.
H
c,i
=
π
d
(6.16)
When the applied magnetic field is beyond the threshold, the deforma-
tion of the liquid crystal (the director field) increases with an increasing
field.
The deformation of the director can be probed by optical transmis-
sion, electric capacitance, conoscopic pattern,
etc
. The experimental set-up
