Download liquid crystals

LIQUID CRYSTALS
Bronwyn Boos
C.6.1; describe the meaning of
the term liquid crystals
 Liquid crystals are fluids that have
physical properties (electrical, optical
& elasticity) dependent on molecular
orientation relative to some fixed axis
in the material
 Ex. graphite, cellulose, DNA
 ***Liquid crystals may not always be in
a liquid-crystal phase
C.6.2; distinguish between
thermotropic and lyotropic
THERMOTROPIC
 Materials are pure substances that
show liquid crystal behavior over a
temp. range between solid and liquid
states.
 EX. Biphenyl nitriles(LCDs), calculator
screens.
C.6.2; distinguish between
thermotropic and lyotropic
LYOTROPIC
 Solutions that show the liquid-crystal
state at certain concentrations.
 Ex. Soap solution and water.
C.6.3; describe liquid-crystal state
(arrangement of molecules) && explain
thermotropic behavior.
 Within the thermotropic liquid crystal
phase the rod-shaped molecules
which are typically about 2.5 x 10⁻9
meters in length exist in groups or
domains.
 Molecules can flow and are randomly
distributed as in a liquid but within
each domain they all point in the
same direction *Nematic Phase.
C.6.3; describe liquid-crystal state
(arrangement of molecules) && explain
thermotropic behavior.
 As temperature increases orientation
becomes increasingly more disrupted
until the directional order is lost and
normal liquid phase is formed.
C.6.4; principles of liquid-crystal
display devices
 Liquid-crystal molecules are polar
orientation can be controlled by an
applied electric field.
 Orientation of molecules affects ability
of the liquid crystal molecules to
transmit light.
 In the liquid crystal displays(digital
watches, calculators, laptops) small
voltage is applied across a thin film of
the material.
C.6.4; principles of liquid-crystal
display devices
 Advantage: use extremely small
electric currents.
 Disadvantage: they only work within a
certain temp. range, explains why
laptop screens can give hot & cold
temperatures.
C.6.5; properties needed for substance
to be used in liquid-crystal displays.
 Chemically stable
 Liquid-crystal phase stable over a
suitable range of temperatures
 Polar in order to change the
orientation when a electric field is
applied
 Rapid switching speed
THE
END