liquid crystals and their applications

A highly usefull and informative powerpoint presentation for all science students

1. Muhammad Minhas Azeem Roll No 7616 Govt College University Faisalabad Liquid Crystals and their Applications Department of Applied Chemistry GC University, Faisalabad

2. Learning Objectives What are liquid crystals? What are stuctures of liquid crystals? What does Thermotropic and Lyotropic mean? The different types of liquid crystal and their arrangement? Working of LCDs? Applications of Liquid crystals?

3. States of mattters 1: Solid 2 : Liquid 3: Gass 4:Liquid crystals 1 :Solid All Soilds have fix shape, fix volume, ductile and high melting and boiling point. It is due to solids have high attrective forces among the atoms and molecules which holds the atom together. SiO² Quartz

4. Liquid Stucture of liquid molecules Attractive forces between the molecules is weak as compared to the soild but strong as compair to gass. The molecules of liquids have more empty spaces as compair to the soild , move aroud with each other but molecules remain close to each other so fluid donot have fix shape and adapted the shape of container .

5. Gas Stucture of gas molecules Gases have less attractive forces among the molecules is weak. The molecules are faraway from each. Gases move randomly so the molecules of gass will expand and fill the container .

6. Liquid Crystals What is a liquid crystal? What is so special about liquid crystals ? A liquid crystals is a phase between solid and liquid states(phases )

7. Examples Example of a compound that shows no LCs phase solid crystalline water; 3- (dimensional) degrees of order liquid water 0 degrees of order gaseous water 0 degrees of order Example of a compound that shows LCs phases 3 degrees of order Looks like milk 1 degree of order 0 degrees of order

8. Phase change

9. A Brief History of LCs Liquid crystals was discoverd by Reinitzer and Lehmann in 1888 . cholesteryl benzoate showed two melting points each. The crystal of this material melted at 145.5 o C into a cloudy fluid, which upon further heating to 178.5 o C became clear Lehmann observed by using polarised optical microscope “and observed crystal that were nearly liquid

10. History In 1973 the discovery of the most technologically and commercial important class of liquid crystals , 4-alkyl-4-’cyanobiphenyl. This material found in calculators or mobile phones Reinitze

11. LCD: Multi Disciplinary Area of Research Theory, law and various Physical properties Device (manufactures) Technological application Preparation of various types of liquid crystalline compounds and characterisation

12. Crystals vs Liquid Crystals A crystal is a highly ordered structure which possesses long-range positional & orientational order For many substances these two types of order are destroyed simultaneously when the crystal melts to form a liquid For some substances, these orders are destroyed in stages. These are liquid crystals

13. Properties of liquid crystals Liquid crystal can flow like a liquid, due to loss of positional order Liquid crystal is optically birefringent, due to its orientational order Transition from crystalline solids to liquid crystals caused by a change of temperature – gives rise to THERMOTROPIC liquid crystals Substances that are most likely to form a liquid crystal phase at a certain temperature are molecules that are ELONGATED & have some degree of RIGIDITY

14. Typical chemical structures Cholesterol ester Phenyl benzoates Surfactants such as polyethylene-oxides, alkali soaps, ammonium salts, lecithin Paraffins Glycolipids Cellulose derivatives

15. Types of liquid crystals

16. Types of Liquid Crystals

17. Benzene-hexa-n-alkanoate derivatives banana-shaped   disk-like molecules  calamitic LCs

18. Comparision betweenThermotropic and Lyotropic THERMOTROPIC Absence of solvent Rigid organic molecules Depends on Temperature Structures: Smectic Nematic Cholesteric LYOTROPIC In solvent Surfactants Depends on Temperature, Concentration, salt, alcohol Structures: Lamellar Hexagonal etc

19. LYOTROPIC LCs Lyotropic LCs are two-component 1: Hydrophilic polar“ head 2: Hydrophobic “tail Examples molecules of soaps phospholipids (present in cell memberane s)

20. LYOTROPIC LCs

21. As temperature increases … The first liquid crystal phase is the smectic A , where there is layer-like arrangement as well as translational and rotational motion of the molecules. A further increase in temperature leads to the nematic phase , where the molecules rapidly diffuse out of the initial lattice structure and from the layer-like arrangement as well. At the highest temperatures, the material becomes an isotropic liquid where the motion of the molecules changes yet again.

22. The Arrangement of Molecules in the Nematic, Smectic, and Cholesteric Liquid Crystal Phases

23. Stuctural phases of liquid crystal Nematic   Nematic  drived from the  Greek   word, ‘ nema ’’ which means "thread". No possitional order Molecules in same direction When temperatures is incrase molecules will be allign immediately In nematic crystal phase molecules are arranged paralell

24. Nematic liquid crystals are widely used in electro-optic display devices The classical examples of LC displaying a nematic mesophase in the Cynobiphenyl

25. Cholesteric The first liquid crystal Cholestericthat was observed through a polarising microscope is cholesteryl benzoate. Thus, CHOLESTERIC liquid crystal OR chiral nematic liquid crystal E.g. cholesteryl benzoate: LC 147C, isotropic 186C Cholesteric liquid crystals have great potential uses as sensors Thermometer fashion fabrics that change colour with temperature display devices

26. In CHOLESTERIC phase, there is orientational order & no positional order, BUT, director is in HELICAL ORDER. The structure of cholesteric depends on the PITCH, the distance over which the director makes one complete turn One pitch - several hundred nanometers Pitch is affected by:- Temperature Pressure Electric & magnetic fields

27. SMECTIC S MECTIC phase occurs at temperature below nematic or cholesteric Molecules align themselves approx. parallel & tend to arrange in layers Not all positional order is destroyed when a crystal melts to form a smectic liquid crystal Chiral smectic C liquid crystals are useful in LCDS

28. Smectic S MECTIC phase occurs at temperature below nematic or cholesteric Molecules align themselves approx. parallel & tend to arrange in layers Chiral smectic C liquid crystals are useful in LCDS Eample : 4,4’’’ – Bis-nonyloxy-[1,1’;1’’;4’’,1’’’] quaterphenyl (2)

29. LIQUID CRYSTAL POLYMERS When liquid crystal polymers solidify, the liquid crystal structure ‘freeze in’ This results in materials of high tensile strength & in some cases unusual electro-optical behaviour E.g. Kevlar aramid fibre – bullet-proof vest & airplane bodies (aromatic polyamide)

30. Technological Application 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 camcorders Fishfinders Thermometers Where are liquid crystals used?

31. Applications Construction of LCD

32. Conclusion We know today that many chemical compounds can exist in the liquid crystal state, such as cholesteryl benzoate. The world can focus on ways to make this product useful in society. Over the last century many applications such as the detection of hot points in microcircuits, the findings of fractures or tumors in humans and the conversion of infared images have become accessible due to the understanding of pitch in a liquid crystal.

33. References 1 : P.G de Gennes, Port.j , 2010 “The Physics of Liquid Crystals”, ref 5. 2: M. J. Stephen, Excellent review of basic properties 3: J. P. Straley “Physics of liquid crystals”, Ref. [2]. 4: D. Fincham, rotational motion of linear molecules, 1984 , 47–48. 5: http://www.slideshare.net/Nawarajintermediate/liquid-crystal-and-its-application# 6: Stegemeyer H, Blumel T, Hiltrop K, Onusseit H and Porsch F, Liq. Cryst. 1986,1-28. 7: Tanimoto K and Crooker P,1985, Phys. Rev. A 32 1893-5. 8: Tsvetkov V, Acta Physicicochim (USSR) , 1942 ( 16- 132). 9: van der Meer B Wand Vertogen G, Phys. Lett, 1976 . 59A( 279-81). 10: Wright D C and Mermin N D, Phys. Rev, 1985 . A 31 3498-500. 11:Thoen J. 1988 Phys. Rev. A 37 1754-9 12 Tsvetkov V 1942 Acta Physicicochim (USSR) 16 132 13 Tanimoto K and Crooker P P 1984 Phys. Rev. A 29 1566-7 13 Tanimoto K, Crooker P P and Koch G C 1985 Phys. Rev. A 32 1893-5