Chemistry Reference
In-Depth Information
Helix Direction
Smectic
Layers
Grain Boundaries
Screw Dislocations
Molecules
Figure 1.10.
The TGB phase of liquid crystals.
(From Goodby
et al
.,
1993.
Reproduced by permission of Taylor & Francis,
<
http://www.tandf.co.uk/journals/
tf/02678292.html
>
)
would reasonably expect it to appear between the cholesteric and smectic
A, or smectic C phases.
1.4.6. Cubic phases
1.4.6.1. D phase
The D phase is the one cubic liquid crystal phase which was discovered
independently in 1957 by G. Gray (Gray
et al
., 1957) and D. Demus (1957)
when they were studying the following compounds
where R is either
CN, and n = 16 or 18. These compounds
display a phase between the S
A
(or N) and S
C
phase and were called the
Smectic D, S
D
phase. Actually the D phase does not have a layered structure
that is characteristic of all smectic phases. The structure has been studied
in detail by Etherington
et al
. (Etherington
et al
., 1985, 1986) through
X-ray diffraction, a second-harmonic-generation experiment and modeling.
The space group and molecular packing of the phase was proposed. It was
thus suggested that it was better to call the S
D
phase the D phase.
−
NO
2
or
−
