FSc Notes Chemistry Part 1 Chapter 4 Liquids and Solids Lecture 5
Capillary Action:
“The rise of a liquid in a capillary tube is known as
capillary action”. A capillary tube is a thin glass tube with a small opening.
In case of liquids whose cohesive force are weak and adhesive forces are
stronger have the ability to attach with the wall of capillary tube and can
rise in it. Such liquids are called wetting liquids. Water is a best example
such liquids show capillary action. On the other hand liquids which have strong
cohesive and weak adhesive forces do not show capillary action because their
molecules do not stick to the walls of capillary tube. Such liquids are known
as non-wetting liquids. Best example is mercury (Hg).
Liquid Crystal:
The substances which are like semi solids and have
properties of both liquid and solids are known as liquid crystals.
Such substances are semi-solids as well as semi-liquids
because they have properties of both liquids and sold (crystalline) substances.
Liquid crystals show optical properties which are the
characteristics of crystalline solids. Similarly liquid crystals show that the
properties like surface tension and viscosity which are the characteristics of
liquids.
Similarly a crystalline solid is anisotropic but liquid crystals
are isotropic.
If a solid is heated, then just near to its melting point it
converts into a turbid shape or as a suspension i.e. a liquid containing heated
further then we get a clear liquid. This turbid form of the substance may be
termed as liquid crystal.
Uses of Liquid Crystal:
Liquid crystals have got so many important applications.
Many of the organic compounds and biological tissues behave as liquid crystals.
Some important applications of liquid crystal are.
- Liquid crystals are used as temperature sensors. They get different color at different temperatures due to diffraction of light falling upon them.
- Liquid crystals can also be used to find the point potential of failure in electrical circuits.
- Liquid crystals are used as solvent in chromatography.
- liquid crystal screens are used in oscillographs ant TV display.
- Room thermometers have liquid crystal with a particular temp range. As the temp changes figures show up in different colors.
- liquid crystalline substance are used to locate the veins arteries, infections and tumors. The infected areas of the body are warmer than other areas. Thus when liquid crystalline substance touch the infected areas their color is changed and thus the infection is detected. The specialists can use the technique of skin thermograph to detect blockage in veins and arteries.
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