Bronwyn Boos LIQUID CRYSTALS
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