classification of liquid crystals and some applications of liquid crystals

1. LIQUID CRYSTALS
AsadUllah
Rehan Khan
Fazil Ahmed

2. STATES OF MATTER:
Solids Liquid CrystalGasLiquid

3. WHAT ARE LIQUID
CRYSTALS.?
LIQUID CRYSTALS HAVE THE ORDERING
PROPERTIES OF SOLIDS BUT THEY FLOW
LIKE LIQUIDS.

4. EXAMPLES:
MOST CONTEMPORARY
ELECTRONIC DISPLAYS USE
LIQUID CRYSTALS. LCD’S
SOLUTIONS OF SOAP AND
DETERGENTS
TOBACCO MOSAIC VIRUS
SOME CLAYS.

5. HISTORY:
In 1888, FRIEDRICH REINITZER ,prepared
CHOLESTERYL BENZOATE, The First Liquid Crystal.

6. LIQUID
CRYSALS
THERMOTROPIC
NEMATIC LIQUID
CRYSTALS
SMECTIC LIQUID
CRYSTALS
SMECTIC-A
SMECTIC-B
SMECTIC-C
CHOLESTRIC
LIQUID CRYSTAL
LYOTROPIC
CLASSIFICATION:

7. 1.THERMOTROPIC
2.LYOTROPIC
INTRODUCTION

8. THERMOTROPIC LC’S:
• A liquid crystal is Thermotropic if the order of its components is
determined or changed by TEMPERATURE.

9. STRUCTURE:
CHOLESTEROL BENZOATE,P-AZOXY PHENETATE

10. APPLICATIONS:
Temperature and
pressure Sensors Display Screens Electro optic display

11. Classification of Liquid Crystals
based on symmetry

12. NEMATIC
LIQUID CRYSTAL
1.DEFINITION
2.PROPERTIES
3.USES AND APPLICATIONS

13. DEFINITION
• A NEMATIC LIQUID CRYSTAL IS A TRANSPARENT OR
TRANSLUCENT LIQUID THAT CAUSES THE POLARIZATION OF
LIGHT WAVES TO CHANGE AS THE WAVES PASS THROUGH THE
LIQUID.

14. PROPERTIES
 Low Viscosity
 Turbid and Anisotropic

16. SMECTIC LIQUID
CRYSTAL
CLASSIFICATION
APPLICATIONS

17. DEFINITION & PHASES:
• MOLECULES SHOW TRANSLATIONAL ORDER. SO THERE ARE 3
TYPES OF SMECTIC LIQUID CRYSTAL (A,B&C).
• THEY FLOW IN LAYERS AS IF DIFFERENT SHEETS ARE
GLIDING OVER ONE ANOTHER
• THESE ARE UNAFFECTED BY MAGNETIC FIELD.

18. SMECTIC A:
• THEY SHOW LAYERED STRUCTURE
• NO LONG RANGE MOLECULAR ORDER AND EACH LAYER OF
SMECTIC A IS DIMENSIONAL LIQUID
• OPTICALLY ACTIVE

19. SMECTIC B
• THEY FORMED LAYERED STRUCTURES AND HAVE PERIODICITY
AND RIGIDITY OF 2D LIQUIDS.
• MOLECULAR ORDER IS FOUND IN EACH LAYER OF LIQUID
CRYSTAL AS EVIDENT FROM X-RAY DIFFRACTION RESULTS.
• THESE ARE NOT FLEXIBLE BUT APPEARS AS THE MOST ORDERED
PHASE AMONG (A,B& C)

20. SMECTIC C
•In the smectic c phase, the constituent molecules are titled in
the smectic layers
•The Smectic C liquid crystal is made of compounds having
lateral components of dipole moments

22. APPLICATION:
• IT CAN INCREASE THE SENSITIVITY OF THE COLOUR RESPONSE.
• IN LASER WRITING BLACK BOARDS-DISPLAY DEVICES USE OF
SMECTIC –A PHASE
• SMECTIC C ,EXHIBITS FERRO ELECTRIC PROPERTIES, HENCE
USED IN MAKING VERY FAST SWITCHING DISPLAYS

23. CHOLESTRIC
LIQUID
CRYSTAL:
1.DEFINITION
2.PROPERTIES
3.USES

24. DEFINITION
• A CHOLESTERIC LIQUID CRYSTAL DISPLAY (CHLCD) IS A
DISPLAY CONTAINING A LIQUID CRYSTAL WITH
A HELICAL STRUCTURE AND WHICH IS THEREFORE CHIRAL.
• CHOLESTERIC LIQUID CRYSTALS ARE ALSO KNOWN
AS CHIRAL LIQUID CRYSTALS.

25. PROPERTIES:
Molecules are chiralic in Nature.
The pitch can be Adjusted by
A slight twist in the plane make these liquid Crystals coloured.
They Show Optical Activity on Twisting.

26. APPLICATIONS
Display Thermal Sensors

28. LYOTROPIC LIQUID
CRYSTALS

29. LYOTROPIC LC’S
• FORMED BY DISSOLVING AN AMPHIPHILIC MESOGEN IN A
SUITABLE SOLVENT,
• AMPHIPHILIC MOLECULES COMPRISE A WATER-LOVING
HYDROPHILIC ATTACHED TO A WATER-HATING,
'HYDROPHOBIC' GROUP.

30. Pictorial Representation:

31. STRUCTURE :• ROD-LIKE MACROMOLECULES
• THESE ARE CLOSER IN ARCHITECTURE TO THERMOTROPIC
LIQUID CRYSTALLINE PHASES THAN TO THE CONVENTIONAL
LYOTROPIC PHASES.

32. EXAMPLES
• SALTS OF FATTY ACIDS,
• PHOSPHOLIPIDS.
• DETERGENTS.
• A MIXTURE OF SOAP AND WATER IS AN EVERYDAY EXAMPLE.

33. APPLICATIONS
•USED IN KEVLAR •DNA Structure

34. o LIQUID CRYSTAL CAN FLOW LIKEA LIQUID, DUE TO LOSS OF
POSITIONAL ORDER
o LIQUID CRYSTAL IS OPTICALLY BIREFRINGENT, DUE TO ITS
ORIENTATIONAL ORDER
o TRANSITION FROM CRYSTALLINE SOLIDS TO LIQUID CRYSTALS
CAUSED BY A CHANGE OF TEMPERATURE – GIVES RISE TO
THERMOTROPIC LIQUID CRYSTALS
o SUBSTANCES THAT ARE MOST LIKELY TO FORM A LIQUID CRYSTAL PHASE
AT A CERTAIN TEMPERATURE ARE MOLECULES THAT ARE ELONGATED &
HAVE SOME DEGREE OFRIGIDITY
PROPERTIES

35. TECHNICAL APPLICATIONS :
 LIQUID CRYSTALS CAN BE FOUND IN THE FOLLOWING DEVICES:
 DIGITAL WATCHES
 POCKET TVS
 GAS PUMPS
 PARKING METERS
 TELECOMMUNICATIONS
 CELL PHONES AND PAGERS
 HIGH-SPEED COMPUTING
 DIGITAL SIGNS
 ELECTRONIC GAMES
 PERSONAL DIGITAL ASSISTANTS
 ELECTRONIC BOOKS
 CALCULATORS
 DIGITAL CAMERAS AND CAMCORD
 FISHFINDERS
 THERMOMETERS

36. CONCLUSION
• THE FUTURE HAS JUST BEGUN.
• THE NEED FOR LIQUID CRYSTAL APPLICATION IS GROWING IN THE
ELECTRONICS FIELD
• THEY REPLACED CATHODE RAY TUBE BY LIQUID CRYSTALS

37. REFERENCE
• 1 S.CHANDRASEKHAR, “LIQUID CRYSTALS”
• 6 G. W.GRAY AND J. W-GOODBY, I1SMECTIC LIQUID CRYSTALS -
TEXTURES
• AND STRUCTURESY(LEONARD HILL, 1984).