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The smectic phases, which are found at lower temperatures than the
nematic, form well-defined layers that can slide over one another in a
manner similar to that of soap (fig.4.5.1b) . The word "smetic" originates
from the Latin word "smecticus", meaning cleaning, or having soap like

properties. The smectics are thus positionally ordered along one direction.
The chiral nematic phase exhibits chirality (handedness) (fig.4.5.1c) .
This phase is often called the cholesteric phase because it was first

observed for cholesterol derivatives. Only chiral molecules (i.e., those that
have no internal planes of symmetry) can give rise to such a phase. This
phase exhibits a twisting of the molecules perpendicular to the director,
with the molecular axis parallel to the director. The finite twist angle

between adjacent molecules is due to their asymmetric packing, which
results in longer-range chiral order.
Applications of Liquid Crystals

Liquid crystal technology has had a major effect many areas of science and
engineering, as well as device technology. Applications for this special
kind of material are still being discovered and continue to provide

effective solutions to many different problems.
Liquid Crystal Displays

The most common application of liquid crystal technology is liquid crystal
displays (LCDs.)A liquid-crystal display (LCD) is a flat panel display,
electronic visual display, or

video display that uses the
light modulating properties
of liquid crystals. Liquid
crystals do not emit light

directly.Each pixel of an
LCD (fig.4.5.2)typically
consists of a layer of

molecules aligned between
two transparent electrodes,
and two polarizing filters
Figure 4.5.2 (parallel and perpendicular),

the axes of transmission of
which are (in most of the
cases) perpendicular to each other. Without the liquid crystal between the

polarizing filters, light passing through the first filter would be blocked by
the second (crossed) polarizer.

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