Chemistry Reference
In-Depth Information
Figure 1.15.
The typical phase diagram of amphiphilic molecules. (From Collings,
1990.)
they may become liquid crystals when subjected to certain external condi-
tions, such as pressure, electric field, magnetic field, irradiation,
etc.
The
liquid crystal phase may also be induced when two non-liquid crystalline
materials are mixed together.
1.5. CONTINUUM THEORY OF LIQUID CRYSTALS
1.5.1. Order parameter
The atoms in crystals are not always fixed in a perfectly ordered position
except at the absolute temperature! Due to the thermal movement, atoms
more or less deviate from their equilibrium position. For the same reason,
the orientational order in liquid crystals is not perfect either. Because of
the thermal fluctuation, the orientation and position of liquid crystals vary
constantly. If the positions and orientations of liquid crystal molecules are
frozen at a moment in time, the picture should look like that shown in
Figure 1.5. The molecules tend to align along a preferred direction, but
imperfectly. This preferred direction is defined as the director
n
. Because
the molecules are moving all the time, they are not fixed at a constant
