Page 88 - 4498

Optical Imaging

An application of liquid crystals that is only now being explored is optical
imaging and recording. In this technology, a liquid crystal cell is placed
between two layers of photoconductor. Light is applied to the

photoconductor, which increases the material's conductivity. This causes
an electric field to develop in the liquid crystal corresponding to the
intensity of the light. The electric pattern can be transmitted by an

electrode, which enables the image to be recorded. This technology is still
being developed and is one of the most promising areas of liquid crystal
research.

Other Liquid Crystal Applications

Liquid crystals have a multitude of other uses. They are used for
nondestructive mechanical testing of materials under stress. This technique

is also used for the visualization of RF (radio frequency) waves in
waveguides. They are used in medical applications where, for example,
transient pressure transmitted by a walking foot on the ground is measured.

Low molar mass (LMM) liquid crystals have applications including
erasable optical disks, full color "electronic slides" for computer-aided
drawing (CAD), and light modulators for color electronic imaging.
As new properties and types of liquid crystals are investigated and

researched, these materials are sure to gain increasing importance in
industrial and scientific applications.

5.Phase Transition

5.1First-Order and Second Order Phase Transitions

A phase transition is the transformation of a thermodynamic system
from one phase or state of matter to another one by heat transfer. The term
is most commonly used to describe transitions between solid, liquid and

gaseous states of matter, and, in rare cases, plasma. A phase of a
thermodynamic system and the states of matter have uniform physical
properties, because of their different mass. During a phase transition of a

given medium certain properties of the medium change, often

88