Surfactants Introduction to Liquid Crystals

1. SurfactantsIntroduction toLiquid Crystals Kausar Ahmad Kulliyyah of Pharmacy

2. Properties of liquid crystals Types of liquid crystals Thermotropic nematic smectic cholesteric Lyotropic structures application NIOSOMES Contents PHM2213 Physical Pharmacy 2, 2011/12

3. Synergistic Effects of Surfactants • Observed when surfactants having relatively similar structure or ionic property are mixed • Resulted in the formation of liquid crystal structures or complexes at the interface by intermolecular interactions between surfactants • Examples • Anionic and nonionic in synthetic latex emulsion polymerisation, • Mixture of a dispersant and a hydrating agent to increase dispersion stability in agricultural chemicals PHM2213 Physical Pharmacy 2, 2011/12

4. STATES OF MATTER • Common states: • solid • liquid • gas • Matter can exist in other states PHM2213 Physical Pharmacy 2, 2011/12

5. LIQUID CRYSTALS • A state that occurs between a solid & a liquid • Possess properties characteristics of both liquids & crystalline solids • Also possess properties not found in either liquids or solids • May response to external perturbations & some changes colour with temperature PHM2213 Physical Pharmacy 2, 2011/12

6. 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. E.g. Slide 17 PHM2213 Physical Pharmacy 2, 2011/12

7. 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. Try slide 29 PHM2213 Physical Pharmacy 2, 2011/12

8. Typical chemical structures • cholesterol ester • phenyl benzoates • surfactants such as polyethylene-oxides, alkali soaps, ammonium salts, lecithin • paraffins • glycolipids • cellulose derivatives PHM2213 Physical Pharmacy 2, 2011/12

9. Typical applications • LCD displays • dyes (cholesterics) • advanced materials (Kevlar) • membranes • temperature measurement (by changing colours) • solvents for GC, NMR, reactions, etc. • Drug delivery PHM2213 Physical Pharmacy 2, 2011/12

10. Types of liquid crystals Thermotropic • Phase transition depends on temperature • Nematic • Smectic • Cholesteric Lyotropic • Phase transition depends on temperature & concentration PHM2213 Physical Pharmacy 2, 2011/12

11. 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. PHM2213 Physical Pharmacy 2, 2011/12

12. Nematic • Simplest form is a nematic liquid crystal i.e. long-range orientational order but no positional order • The preferred direction is known as director PHM2213 Physical Pharmacy 2, 2011/12

13. Nematic… • 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) • 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 • Thus, possible to have microscopic order & macroscopic order • Nematic liquid crystals are widely used in electro-optic display devices PHM2213 Physical Pharmacy 2, 2011/12

14. Cholesteric • The first liquid crystal that 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 PHM2213 Physical Pharmacy 2, 2011/12

15. 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 PHM2213 Physical Pharmacy 2, 2011/12

16. Smectic • SMECTIC 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 PHM2213 Physical Pharmacy 2, 2011/12

17. LIQUID CRYSTAL POLYMERS • Can form nematic, cholesteric, smectic • 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) PHM2213 Physical Pharmacy 2, 2011/12

18. Examples of phase changes Cholesterylmyristate 79C 85C 71C isotropic solid smectic A cholesteric 4, 4’-di-heptyloxyazoxybenxene 74C 94C 124C nematic solid smectic C isotropic PHM2213 Physical Pharmacy 2, 2011/12

19. 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 Thermotropic vs Lyotropic PHM2213 Physical Pharmacy 2, 2011/12

20. Structure formation in surfactant solution monolayer hexagonal rod micelle Oil/alcohol REVERSE HEXAGONAL Reverse micelle Formation of MICROEMULSION bilayer PHM2213 Physical Pharmacy 2, 2011/12

21. Effect of temperature and concentration on the structure of lyotropic liquid crystals PHM2213 Physical Pharmacy 2, 2011/12

22. SURFACTANT VESICLES [A] Phospholipids (e.g. lecithin) + H2O ----> phospholipid vesicles or liposomes [B] Liposomes + (long chain) stearylamine -------> tve charge liposome (carriers for DNA) [C] Liposomes + dicetyl phosphate ----- - ve charge liposome PHM2213 Physical Pharmacy 2, 2011/12

23. Vesicles • Bilayers that fold into a 3D structure • 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. • Lipids found in biological membranes spontaneously form vesicles in solution. PHM2213 Physical Pharmacy 2, 2011/12

24. Application of Liposomes • can encapsulate: • drugs, • proteins, • enzymes • administered intravenously, orally or intramuscularly • decrease toxicity • increase specificity of drug uptake • enable slow release PHM2213 Physical Pharmacy 2, 2011/12

25. Problems with phospholipids • phospholipids undergo oxidative degradation • handling & storage must be under nitrogen • expensive PHM2213 Physical Pharmacy 2, 2011/12

26. Formation of liquid crystals using surfactants Anionic e.g. alkane sulfonates Cationic e.g. hexadecyltrimethyl ammonium bromide Amphoteric e.g. alkyl betaines • Due to toxicity of ionic surfactants, the vesicles are not used for drug delivery Non-ionic e.g. alcohol ethoxylates R-O-(CH2CH2O) m H m: 2-20, R : mixed; alkyl group C8C18 PHM2213 Physical Pharmacy 2, 2011/12

27. Niosomes • Non-ionic + cholesterol -> NIOSOMES • These vesicles prolong the circulation of entrapped drug • Properties depend on • Composition of bilayer • Method of productione.g. cholesterol & single alkyl-chain non-ionic surfactant with a glyceril head group PHM2213 Physical Pharmacy 2, 2011/12

28. Examples of niosome applications • Ketoconazole niosomes were prepared by using surfactant (Tween 40 or 80), cholesterol and drugSatturwar PM; Fulzele SV; Nande VS; Khandare, JNIndian Journal of Pharmaceutical Sciences. 2002 Mar-Apr; 64(2): 155-8 • Use for topical immunisation - Bovine serum albumin (BSA)loaded niosomes composed of sorbitanmonostearate/sorbitantrioleate (Span 60/Span 85), cholesterol and stearylamine as constitutive lipidsSanyogJain, S. P. Vyas, Journal of Pharmacy and Pharmacology Vol. 57, No. 9, pages 1177 (2005) PHM2213 Physical Pharmacy 2, 2011/12

29. References http://www.lci.kent.edu/lc.html#Description http://liqcryst.chemie.uni-hamburg.de/lc_lc.php http://www.glycoprojects.kimia.um.edu.my/website/Glyco/ (carbohydrate liquid crystal) http://www.gla.ac.uk/~jmb17n/conacher.pdf (niosomes) http://plc.cwru.edu/tutorial/enhanced/files/lc/phase/phase.htm Kreuter, J. (ed.) (1994). Colloidal Drug Delivery Systems. New York: Marcel Dekker, Chapter 3 & 4 PHM2213 Physical Pharmacy 2, 2011/12

30. http://plc.cwru.edu/tutorial/enhanced/lab/lab.htm PHM2213 Physical Pharmacy 2, 2011/12