What is Liquid Crystals 2022 | Basic Concept of Liquid Crystals in Chemistry |

The intermediate turbid liquid phase of some solids between the solid phase and clear liquid phase, showing some properties of liquids and some properties of solids is called liquid crystal.

Discovery of Liquid crystals

Liquid Crystals were first discovered by an Austrian botanist, F – Reinitzer, in 1888. He was studying an organ compound cholesteryl benzoate. This compound becomes milky at 145 ° C and becomes clear at 179 ° C. On cooling reverse process occurs. This turbid milky phase was called liquid crystal.  

Explanation

When a solid is melted, it is converted to a clear liquid. However, many crystalline solids pass through a turbid liquid phase before finally converting into clear liquid This turbid phase is called liquid crystal. A liquid crystalline phase exists between two temperatures, a melting temperature and a clearing temperature.

Properties of Liquid Crystals

Their properties are intermediate between crystals and isotropic liquids.

1. These have some degree of order like solids.

2. These have fluidity like liquids.

3. These have properties such as surface tension, viscosity etc. like liquids.

4. These have optical properties of crystalline solids.

5. These may be isotropic or anisotropic.

Types of Liquid Crystals:

Based on the ordering of particles, liquid crystals can be divided into various types eg nematic, smectic and cholesteric.

Liquid Crystals
Liquid Crystals

Applications

From 1888 until about 30 years ago, liquid crystals were limited to laboratories. But now these have many applications.

1. Liquid crystals have excellent electrical and optical properties.

2. Many organic compounds and biological tissues behave as liquid crystals.

3. Liquid crystals can diffract light. When one of the wavelengths of light is reflected by crystals, they appear coloured. With the temperature change, the distance between layers of molecules of liquid crystals also changes. Hence, the colour of reflected light also changes. Thus, liquid crystals can be used as temperature sensors,

4. With the temperature change, liquid crystals change colour and give a measure of temperature. Thus, these are used to prepare room thermometers, for a definite temperature range.

5. This can be used to find the point of potential failure in electrical circuits

6. Liquid crystals are used in medical diagnosis. These can be used to locate veins, arteries, infections and tumours. It is because these parts are warmer than surrounding tissues, so they can be detected by using temperature-sensitive liquid crystals. This technique is called Skin thermograph.

It is used to

(i)  detect blockages in veins and arteries.

(ii) detect breast cancer at an earlier stage, a layer of temperature-sensitive liquid crystal is painted on the surface of the breast The warm tumour shows up in blue colour.

7. These are used in the display of electrical devices (LCD = liquid crystal display), such as digital watches, calculators and computers. It is because temperature, pressure and electromagnetic fields can change the weak bonding conditions in crystals, hence giving different appearances.

8. In chromatography, liquid crystals are used as solvents

9. Oscillographic and TV displays also use liquid crystal screens.

Read more about Quantum Numbers.

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