Chemistry Reference
In-Depth Information
Figure
6.20.
The
finger-print
texture
of
PBLG
solution
(20%
PBLG
in
dichloromethane,
Mn
= 40000). (From Ritter, 1986.)
pitch and concentration. Figure 6.21 plots the pitch of PBLG in dioxane
(Onagi
et al
., 1980) and hydroxypropyl-cellulose in water (Robinson, 1955,
1961).
Pitch as a function of temperature
The molecular chirality does not necessarily decide the chirality of
cholesteric liquid crystalline polymers because the sample's chirality also
depends on the solvent. PBLG is itself a right-hand molecule. It indeed
forms a right-handed chiral liquid crystalline polymer in dioxane or
trichloromethane, while it forms the left-handed polymer in chloromethy-
lene and chloroethylene. In Figure 6.22, the reciprocal of pitch is plotted
against temperature for PBLG in dioxane and dichloroethylene mixture
with concentration
c
=0
.
1 vol%. With an increasing concentration of
dichloroethylene, the cholesteric liquid crystalline polymer changes gradu-
ally from right-handed to left-handed. In a median value for concentration
of dichloroethylene, 60% at
T
=50
◦
C, the helix is completely unwounded.
It is found that 1
/P
is approximately linear in proportion to tempera-
ture. As temperature increases, the pitch increases until the helical sense
reverses and then decreases (Uematsu, 1984). It was found that the pitch
