Title: Ever wondered what "liquid crystal" is? Here’s an intro
1Ever wondered what "liquid crystal" is?
Heres an intro
2Introduction
Liquid crystal is a state of matter like
liquid, solid, and gas. The term liquid crystal
is used to denote a material that exhibits a
liquid phase under certain conditions. In order
to understand what differentiates a liquid
crystal phase from a liquid or solid phase, it is
necessary to understand what defines these
phases.
3- The difference lies in the order of matter on a
molecular, atomic or subatomic level. Order is a
function of the energy stored within matter, and
hence a function of the temperature of matter. - Thus, one could say that temperature equals
motion. There is no motion at absolute zero
temperature (0 Kelvin). - Very close to absolute zero, a state of matter
called the Bose-Einstein condensate can exist. - A little further away from absolute zero we have
solids, which are characterized by limited motion
of the molecules, atoms and ions that make up the
material. - This limited motion is a vibration within the
molecule, and an oscillation around a fixed
position. In a crystal for example, the centers
of gravity within the molecules vibrate around
fixed positions on a crystal lattice, while the
general orientation of non-spherical molecules
vibrates around a preferred orientation.
4- When a solid melts, this long range order (fixed
average position, fixed average orientation many
thousands of molecular units across) breaks up. - If both long range orders (position and
orientation) dissipate at the same time as when
the melting point is reached, a liquid phase is
formed. - In a liquid, there still is some level of order,
but only in a short range (i.e. a few molecules
across). The hydrogen bonds between water
molecules are a good example. - When, with increasing temperature, this short
range order gets lost and the molecules become
completely independent in their motion, we speak
about a gas or vapor. - Finally, when electrons or other sub-atomic
particles lose their order with respect to the
rest of the molecule, we speak about plasma.
5- Nature does not require that each phase is
formed Some materials can go from solid to gas
without a liquid phase. Neither does nature
require that positional and orientational order
get lost in one step and at the same temperature. - Depending on environmental conditions such as
pressure or solvent concentration in a mixture,
phases may be skipped or additional phases may
appear when changing the temperature of a
material. - If positional order gets lost at the melting
point, but orientational long range order is
maintained up to a higher temperature, a liquid
crystal phase is formed. - The temperature at which all orientational long
range order gets lost is called clearing point,
as at such temperature a typically milky liquid
crystal turns into a clear fluid.
6- Positional long range order can get lost in
steps while orientational order is maintained. As
a result there can be many liquid crystal phases
with different geometry and distinct phase
transition temperatures between them. In some
phases the liquid crystal is aligned in layers.
They are called smectic phases and letters are
used to differentiate different geometries
(smectic A, smC, smI). Columnar phases have
molecules aligned in columns. The liquid crystal
phase with no long range positional order is
called a nematic phase and it is most widely used
in displays.
Liquid crystal phases are useful in displays
because they interact with light and electric
fields like crystals, but they can move (flow)
like liquids, making it possible to use electric
fields to change their effect on light.
7- A typical temperature range of the liquid crystal
phase(s) of a single material is only a few
degrees. For most materials, that range is well
above room temperature. In order to make liquid
crystals practical for use in LCD displays, they
need to be blended. - Mixtures of liquid crystal materials can be
formulated so that their temperature range is
wide and falls within the operating temperature
range requirements of modern electronics devices. - Liquid Crystal Fluid suppliers engage in
researching new material groups, synthesizing
materials, and blending mixtures to achieve the
physical properties defined by display
manufacturers. Blends contain some 10-25 single
substances.
8- A typical calamitic liquid crystal material that
may be used in such blends is 5OCB
In a volume model it would appear like this
9Or simplified like a rod or cigar
10Source
- To read more visit at http//newvisiondisplay.com
/liquid-crystal/
11Thank You
A presentation by
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