What is an LCD (Liquid Crystal Display)? How does it work

We use items containing LCDs daily. Being endowed with more advantages than competing technologies, LCDs are predominant. They are thinner, lighter, and draw less power. 1888 saw Friedrich Reinitzer’s discovery of liquid crystals. The Austrian Biochemist observed that on the melting of cholesteryl benzoate, a cloudy liquid was obtained that hardened as the temperature rose. The liquid finally crystallized after having turned blue on cooling. 1968 saw the RCA experimental LCD.

Electricity, Light, Liquid Crystals

Solid, liquid, gaseous are the three common states of matter. Solids have molecules, all pointing the same way. Their position vis-a-vis one another remains the same. Liquids, however, have molecules pointing in all directions. There also exist substances that have states between liquid and solid. Their molecules show properties of both liquid and solid molecules. Liquid crystals, therefore, are neither liquid nor solid.

It is true with experiments that liquid crystals are more liquid than solid. Liquid crystals are sensitive to temperature. They are therefore used for making thermometers.

Liquid crystals get the effect of an electric current. Twisted Nematics are a kind of liquid crystal. They untwist in a certain way when electricity is applied to them. LCDs use twisted nematics to control light passage predictably.

LCD Types

Liquid crystals are generally categorized as thermotropic or lyotropic. Thermotropic liquid crystals react to changes in temperature. They also, to some extent, respond similarly to pressure. Lyotropic liquid crystals build in the manufacture of detergents and soaps. The type of solvent they are mixed with determines the lyotropic liquid crystals’ reaction. Isotropic or nematic thermotropic liquid crystals have a principal difference. While the former are randomly arranged, the molecules of the latter are clearly patterned in an order.

Nematic-Smectic

In the nematic phase, the orientation of the molecules is based on the director. Anything from a magnetic field to a surface that has microscopic grooves in it can be the director. Liquid crystals in the nematic phase can be further classified by how molecules orient themselves concerning one another. The Smectic arrangement creates layers of molecules. There are variations to this phase. In one major type, molecules in one layer tilt at an angle from the previous layer. The chores or chiral nematic type have molecules twisting from one layer to another. This renders a spiral formation.

FLCs-SSFLCs

FLCs or Ferroelectric liquid crystals employ liquid crystal substances that have chiral molecules in a smectic C type of arrangement. The spiral character of these molecules permits the micro switching response time that makes FLCs responsive to liquid displays. SSFLCs or surface stabilized ferroelectric liquid crystals exert controlled pressure through the use of a glass plate. This suppresses the molecule spiral to make switching swifter.

A Simple LCD

Following characteristics make LCD construction possible

• Light is polarizable;
• Liquid crystals change polarized light;
• Electricity changes Liquid crystal structure ;
• Electricity conducting transparent substances.

Take two sheets of polarized glass. A microscopic groove creating polymer can r on the side of the glass without polarizing film on it. Polarizing film and the grooves face the same direction. We subsequently add a coating of nematic liquid crystals to one of the filters. With the filter’s orientation are the first layers of molecules aligned. The grooves cause this to occur. Subsequently, add the second piece of glass with the polarizing film at a right angle to the first sheet. Twisting molecules align until the uppermost layer is at a 90 degrees angle to the bottom. The uppermost layer thus matches the polarized glass filters. Upon striking the first filter, light is polarized.

When light passes through successive layers, the molecules change the light’s plane of vibration. There is alignment with the final layer of molecules. If the second polarized glass filter matches with the final layer, the light passes through.