Chemistry Reference
In-Depth Information
Figure 4.16. A domain full of inversion walls. From top to bottom the polars have
rotated by 90
◦
. The sample is a nematic polymer with the two-dimensional type
mesogenic units.
top. The dark spots may be used as reference for an easier examination of
the two pictures. The dark line with a dark spot in the top picture turns
bright after the polars have rotated by 90
◦
as shown in the bottom picture.
The threaded texture is also often observed for nematics especially when
a thicker film is examined. In this texture disclination lines show up as dark
lines swimming in the sample with thermal motion. The lines are observable
without polars (Figure 4.17) but the thread contrast will be higher when
crossed polars are used. Because of the stopless molecular reorientation with
thermal motion in the sample the old dark lines may disappear and new
ones may form. In cases when the two ends are anchored on the surfaces
the ends will stay where they have been but the thread may swing about.
