Introduction To Liquid Crystals

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Introduction To Liquid Crystals

  1. 1. Surfactants Introduction to Liquid Crystals Kausar Ahmad Kulliyyah of Pharmacy
  2. 2. Contents <ul><li>Properties of liquid crystals </li></ul><ul><li>Types of liquid crystals </li></ul><ul><li>Thermotropic </li></ul><ul><ul><li>nematic </li></ul></ul><ul><ul><li>smectic </li></ul></ul><ul><ul><li>cholesteric </li></ul></ul><ul><li>Lyotropic </li></ul><ul><ul><li>structures </li></ul></ul><ul><ul><li>application </li></ul></ul><ul><ul><li>NIOSOMES </li></ul></ul>
  3. 3. Synergistic Effects of Surfactants <ul><li>Observed when surfactants having relatively similar structure or ionic property are mixed </li></ul><ul><li>Resulted in the formation of liquid crystal structures or complexes at the interface by intermolecular interactions between surfactants </li></ul><ul><li>Examples </li></ul><ul><ul><li>Anionic and nonionic in synthetic latex emulsion polymerisation, </li></ul></ul><ul><ul><li>Mixture of a dispersant and a hydrating agent to increase dispersion stability in agricultural chemicals </li></ul></ul>
  4. 4. STATES OF MATTER <ul><li>Common states: </li></ul><ul><ul><li>solid </li></ul></ul><ul><ul><li>liquid </li></ul></ul><ul><ul><li>gas </li></ul></ul><ul><li>Matter can exist in other states </li></ul>
  5. 5. LIQUID CRYSTALS <ul><li>A state that occurs between a solid & a liquid </li></ul><ul><li>Possess properties characteristics of both liquids & crystalline solids </li></ul><ul><li>Also possess properties not found in either liquids or solids </li></ul><ul><li>May response to external perturbations & some changes colour with temperature </li></ul>
  6. 6. <ul><li>A crystal is a highly ordered structure which possesses long-range positional & orientational order </li></ul><ul><li>For many substances these two types of order are destroyed simultaneously when the crystal melts to form a liquid </li></ul><ul><li>For some substances, these orders are destroyed in stages. These are liquid crystals. E.g. Slide 17 </li></ul>Crystals vs Liquid Crystals
  7. 7. <ul><li>Liquid crystal can flow like a liquid, due to loss of positional order </li></ul><ul><li>Liquid crystal is optically birefringent, due to its orientational order </li></ul><ul><li>Transition from crystalline solids to liquid crystals caused by a change of temperature – gives rise to THERMOTROPIC liquid crystals </li></ul><ul><ul><li>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. Try slide 29 </li></ul></ul>Properties of liquid crystals
  8. 8. Typical chemical structures <ul><li>cholesterol ester </li></ul><ul><li>phenyl benzoates </li></ul><ul><li>surfactants such as polyethylene-oxides, alkali soaps, ammonium salts, lecithin </li></ul><ul><li>paraffins </li></ul><ul><li>glycolipids </li></ul><ul><li>cellulose derivatives </li></ul>
  9. 9. Typical applications <ul><li>LCD displays </li></ul><ul><li>dyes (cholesterics) </li></ul><ul><li>advanced materials (Kevlar) </li></ul><ul><li>membranes </li></ul><ul><li>temperature measurement (by changing colours) </li></ul><ul><li>solvents for GC, NMR, reactions, etc. </li></ul><ul><li>Drug delivery </li></ul>
  10. 10. Types of liquid crystals <ul><li>Thermotropic </li></ul><ul><li>Phase transition depends on temperature </li></ul><ul><ul><li>Nematic </li></ul></ul><ul><ul><li>Smectic </li></ul></ul><ul><ul><li>Cholesteric </li></ul></ul><ul><li>Lyotropic </li></ul><ul><li>Phase transition depends on temperature & concentration </li></ul>
  11. 11. As temperature increases….. <ul><li>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. </li></ul><ul><li>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. </li></ul><ul><li>At the highest temperatures, the material becomes an isotropic liquid where the motion of the molecules changes yet again. </li></ul>
  12. 12. Nematic <ul><li>Simplest form is a nematic liquid crystal </li></ul><ul><li>i.e. long-range orientational order but no positional order </li></ul><ul><li>The preferred direction is known as director </li></ul>
  13. 13. Nematic… <ul><li>Despite the high degree of orientational order , nematic phase as a whole is in disorder i.e. NO MACROSCOPIC ORDER (orientation within a group is similar but not from one group to another) </li></ul><ul><li>Structure of nematic phase can be altered in a number of ways. E.g. electric or magnetic field or treatment of surfaces of the sample container </li></ul><ul><li>Thus, possible to have microscopic order & macroscopic order </li></ul><ul><li>Nematic liquid crystals are widely used in electro-optic display devices </li></ul>
  14. 14. Cholesteric <ul><li>The first liquid crystal that was observed through a polarising microscope is cholesteryl benzoate. Thus, CHOLESTERIC liquid crystal OR chiral nematic liquid crystal </li></ul><ul><li>E.g. cholesteryl benzoate: LC @ 147C, isotropic @ 186C </li></ul><ul><li>Cholesteric liquid crystals have great potential uses as </li></ul><ul><ul><li>sensors </li></ul></ul><ul><ul><li>Thermometer </li></ul></ul><ul><ul><li>fashion fabrics that change colour with temperature </li></ul></ul><ul><ul><li>display devices </li></ul></ul>
  15. 15. <ul><li>In CHOLESTERIC phase, there is orientational order & no positional order, BUT, director is in HELICAL ORDER. </li></ul><ul><li>The structure of cholesteric depends on the PITCH, the distance over which the director makes one complete turn </li></ul><ul><ul><li>One pitch - several hundred nanometers </li></ul></ul><ul><li>Pitch is affected by:- </li></ul><ul><ul><li>Temperature </li></ul></ul><ul><ul><li>Pressure </li></ul></ul><ul><ul><li>Electric & magnetic fields </li></ul></ul>
  16. 16. Smectic <ul><li>SMECTIC phase occurs at temperature below nematic or cholesteric </li></ul><ul><li>Molecules align themselves approx. parallel & tend to arrange in layers </li></ul><ul><li>Not all positional order is destroyed when a crystal melts to form a smectic liquid crystal </li></ul><ul><li>Chiral smectic C liquid crystals are useful in LCDS </li></ul>
  17. 17. LIQUID CRYSTAL POLYMERS <ul><li>Can form nematic, cholesteric, smectic </li></ul><ul><li>When liquid crystal polymers solidify, the liquid crystal structure ‘freeze in’ </li></ul><ul><li>This results in materials of high tensile strength & in some cases unusual electro-optical behaviour </li></ul><ul><li>E.g. Kevlar aramid fibre – bullet-proof vest & airplane bodies (aromatic polyamide) </li></ul>
  18. 18. Examples of phase changes <ul><li>Cholesteryl myristate </li></ul>solid smectic A 71C cholesteric isotropic 79C 85C 4, 4’-di-heptyloxyazoxybenxene solid 74C 94C 124C smectic C nematic isotropic
  19. 19. Thermotropic vs Lyotropic <ul><li>THERMOTROPIC </li></ul><ul><li>Absence of solvent </li></ul><ul><li>Rigid organic molecules </li></ul><ul><li>Depends on Temperature </li></ul><ul><li>Structures: </li></ul><ul><ul><li>Smectic </li></ul></ul><ul><ul><li>Nematic </li></ul></ul><ul><ul><li>Cholesteric </li></ul></ul><ul><li>LYOTROPIC </li></ul><ul><li>In solvent </li></ul><ul><li>Surfactants </li></ul><ul><li>Depends on Temperature, Concentration, salt, alcohol </li></ul><ul><li>Structures: </li></ul><ul><ul><li>Lamellar </li></ul></ul><ul><ul><li>Hexagonal etc </li></ul></ul>
  20. 20. Structure formation in surfactant solution micelle rod hexagonal monolayer bilayer Reverse micelle Formation of MICROEMULSION REVERSE HEXAGONAL Oil/alcohol
  21. 21. Effect of temperature and concentration on the structure of lyotropic liquid crystals
  22. 22. SURFACTANT VESICLES <ul><li>[A] Phospholipids (e.g. lecithin) + H 2 O ----> </li></ul><ul><li>phospholipid vesicles or liposomes </li></ul><ul><li>[B] Liposomes + (long chain) stearylamine -------> </li></ul><ul><li>tve charge liposome (carriers for DNA) </li></ul><ul><li>[C] Liposomes + dicetyl phosphate -----  </li></ul><ul><li>- ve charge liposome </li></ul>
  23. 23. Vesicles <ul><li>Bilayers that fold into a 3D structure </li></ul><ul><li>Vesicles form because they get rid of the edges of bilayers, protecting the hydrophobic chains from the water , but they still allow for relatively small layers. </li></ul><ul><li>Lipids found in biological membranes spontaneously form vesicles in solution. </li></ul>
  24. 24. Application of Liposomes <ul><li>can encapsulate : </li></ul><ul><ul><li>drugs , </li></ul></ul><ul><ul><li>proteins, </li></ul></ul><ul><ul><li>enzymes </li></ul></ul><ul><li>administered intravenously, orally or intramuscularly </li></ul><ul><li>decrease toxicity </li></ul><ul><li>increase specificity of drug uptake </li></ul><ul><li>enable slow release </li></ul>
  25. 25. Problems with phospholipids <ul><li>phospholipids undergo oxidative degradation </li></ul><ul><li>handling & storage must be under nitrogen </li></ul><ul><li>expensive </li></ul>
  26. 26. Formation of liquid crystals using surfactants <ul><li>[A] Anionic </li></ul><ul><li>e.g. alkane sulfonates </li></ul><ul><li>[B] Cationic </li></ul><ul><li>e.g. hexadecyl trimethyl ammonium bromide </li></ul><ul><li>[C] Amphoteric </li></ul><ul><li>e.g. alkyl betaines </li></ul><ul><li>Due to toxicity of ionic surfactants, the vesicles are not used for drug delivery </li></ul><ul><li>[D] Non-ionic </li></ul><ul><li>e.g. alcohol ethoxylates R-O-(CH 2 CH 2 O) m H m: 2-20, R : mixed; alkyl group C 8 C18 </li></ul>
  27. 27. <ul><li>Non-ionic + cholesterol -> NIOSOMES </li></ul><ul><li>These vesicles prolong the circulation of entrapped drug </li></ul><ul><li>Properties depend on </li></ul><ul><ul><li>Composition of bilayer </li></ul></ul><ul><ul><li>Method of production e.g. cholesterol & single alkyl-chain non-ionic surfactant with a glyceril head group </li></ul></ul>Niosomes
  28. 28. Examples of niosome applications <ul><li>Ketoconazole niosomes were prepared by using surfactant (Tween 40 or 80), cholesterol and drug Satturwar PM; Fulzele SV; Nande VS; Khandare, JN Indian Journal of Pharmaceutical Sciences. 2002 Mar-Apr; 64(2): 155-8 </li></ul><ul><li>Use for topical immunisation - Bovine serum albumin (BSA)loaded niosomes composed of sorbitan monostearate/sorbitan trioleate (Span 60/Span 85), cholesterol and stearylamine as constitutive lipids Sanyog Jain1, S. P. Vyas2 , Journal of Pharmacy and Pharmacology Vol. 57, No. 9, pages 1177 (2005) </li></ul>
  29. 29. References <ul><li>http://www.lci.kent.edu/lc.html#Description </li></ul><ul><li>http://liqcryst.chemie.uni-hamburg.de/lc_lc.php </li></ul><ul><li>http://www.glycoprojects.kimia.um.edu.my/website/Glyco/ (carbohydrate liquid crystal) </li></ul><ul><li>http://www.gla.ac.uk/~jmb17n/conacher.pdf (niosomes) </li></ul><ul><li>http://plc.cwru.edu/tutorial/enhanced/files/lc/phase/phase.htm </li></ul><ul><li>J Kreuter (ed.), Colloidal Drug Delivery Systems, Marcel Dekker, New York (1994) Chapter 3&4 </li></ul>
  30. 30. http://plc.cwru.edu
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