Chemistry Reference
In-Depth Information
Fig. 3 Experimental setup
for EOM effect and polarized
FTIR measurements of
nematic gels under electric
fields. For the optical
birefringence measurements,
the initial director of the
specimen has an angle of 45
relative to the crossed
polarizers. For the polarized
FTIR measurements, the
optical axis of the polarizer is
parallel or normal to the
initial director for evaluating
absorbances
A
x
or
A
y
,
respectively, and no analyzer
is used.
l
x
and
l
y
are the
dimensions of the film in the
x
- and
y
-directions,
respectively
sin
2
(
pdDn
eff
/l) where l is the wavelength of a
from the familiar relation
I
/
I
max
¼
He-Ne laser (l
¼
633 nm). The change in film thickness (
d
) was less than 15% in
the
V
0
range examined, and thus the initial thickness was used for the sake of
simplicity in the calculation of
Dn
eff
at each
V
0
.
The electrically induced strains in the
x
- and
y
-directions were measured using
an optical microscope. The dimensional change in the
z
-direction (field axis) is not
directly measurable, but can be straightforwardly estimated from the dimensional
variations in the
x
- and
y
-directions because of the constant volume before and after
deformation.
3 Static Aspects
3.1 Electro-Mechanical Effect
The most prominent feature of the electrical deformation of monodomain nematic
The gel film contracts in the direction of the initial director (
x
-direction) and
elongates in the field direction (
z
-direction) without an appreciable dimensional
change in the
y
-direction normal to both the initial director and the field axis. The
elongation in the
z
-direction is estimated from the dimensional changes in the
x
- and
y
-directions because the gel volume is constant during deformation. It should be
noted that the
y
-direction without dimensional variation is identical to the axis of
rotation of the director. An mpeg movie of this electrical deformation is available in
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