Surfactants Introduction to Liquid Crystals Kausar Ahmad http://staff.iium.edu.my/akausar akausar@iium.edu.my

CONTENTS Properties of liquid crystals Types of liquid crystals Thermotropic Lyotropic Physical Pharmacy 2

SYNERGISTIC EFFECTS OF SURFACTANTS Observed when surfactants having relatively similar structure or ionic property are mixed Resulted in the formation of liquid crystal structures at the interface due to 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 Physical Pharmacy 2

STATES OF MATTER Matter can exist in other states Common states: solid, liquid, gas Matter can exist in other states Physical Pharmacy 2

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 Physical Pharmacy 2

CRYSTAL VERSUS LIQUID CRYSTAL Characteristic Crystal Liquid Crystal Positional order YES/LONG-RANGED NO/SHORT-RANGED Orientational order YES UPON MELTING ORDER LOST COMPLETELY ORDERS LOST IN STAGES Physical Pharmacy 2

PROPERTIES OF LC 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 Physical Pharmacy 2

TYPES OF LC THERMOTROPIC LYOTROPIC Physical Pharmacy 2

THERMOTROPIC LC The first liquid crystal phase is the SMECTIC A layer-like arrangement as well as translational and rotational motion of the molecules. A further increase in temperature leads to the NEMATIC molecules rapidly diffuse out of the initial lattice structure and from the layer-like arrangement as well. At the highest temperatures, the material becomes ISOTROPIC LIQUID Motion of the molecules changes all the time. Physical Pharmacy 2

PROPERTIES OF LC MOLECULES Substances with molecules that are ELONGATED HAVING SOME DEGREE OF RIGIDITY. "Cholesteryl benzoate". Licensed under Public Domain via Commons - https://commons.wikimedia.org/wiki/File:Cholesteryl_benzoate.png#/media/File:Cholesteryl_benzoate.png Physical Pharmacy 2

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 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 e.g. electric or magnetic field: thus, possible to have microscopic order & macroscopic order Nematic liquid crystals are widely used in LCD devices Physical Pharmacy 2

CHOLESTERIC The first LC observed is cholesteryl benzoate. Thus, CHOLESTERIC or chiral nematic Cholesteric liquid crystals widely used in LCD display In CHOLESTERIC phase, there is orientational order & no positional order. At 145.5 °C (293.9 °F) it melts into a cloudy liquid, and at 178.5 °C (353.3 °F) it melts again and the cloudy liquid becomes clear. The phenomenon is reversible. 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 Physical Pharmacy 2

SMECTIC SMECTIC 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 LCD Physical Pharmacy 2

REVERSIBLE CHANGES IN PHASES Cholesteryl myristate 79C 85C 71C Isotropic solid Smectic A Cholesteric 4, 4’-di-heptyloxyazoxybenxene At 145.5 °C (293.9 °F) it melts into a cloudy liquid, and at 178.5 °C (353.3 °F) it melts again and the cloudy liquid becomes clear. The phenomenon is reversible. 74C 94C 124C Nematic Isotropic solid Smectic C Physical Pharmacy 2

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) Physical Pharmacy 2

http://plc.cwru.edu/tutorial/enhanced/lab/lab.htm Click link Physical Pharmacy 2

THERMOTROPIC VS LYOTROPIC Presence of solvents NO YES Depends on Temperature, Concentration, Salt, Alcohol Molecules Rigid organic molecules e.g. cholesterol ester, phenyl benzoates, paraffins , glycolipids, cellulose derivatives Surfactant molecules e.g. polyethylene-oxides, alkali soaps, ammonium salts, lecithin Temperature dependent Structure Smectic , Nematic, Cholesteric Lamellar, Hexagonal etc. Applications LCD displays, Dyes (cholesterics) Advanced materials (Kevlar), Temperature measurement (by changing colours) Biological membranes Drug delivery Physical Pharmacy 2

STRUCTURAL CHANGES FOR LYOTROPIC LC Formation of MICROEMULSION Temperature WATER Inverse phases: Inverse cubic Inverse hexagonal lamellar hexagonal OIL cubic micelles Concentration of surfactant Physical Pharmacy 2

FORMATION OF LIQUID CRYSTALS USING SURFACTANTS Anionic e.g. alkane sulfonates Cationic e.g. hexadecyl trimethyl ammonium bromide Amphoteric e.g. alkyl betaines Non-ionic e.g. alcohol ethoxylates R-O-(CH2CH2O) mH; m: 2-20, R: alkyl group C8-C18 Physical Pharmacy 2

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 Lipids found in biological membranes spontaneously form vesicles in solution. Physical Pharmacy 2

Phospholipids/lecithin + H2O SURFACTANT VESICLES phospholipid/liposome Phospholipids/lecithin + H2O tve charge liposome (carriers for DNA) Liposomes + stearylamine - ve charge liposome dicetyl phosphate Physical Pharmacy 2

APPLICATION OF LIPOSOMES can encapsulate: drugs, proteins, enzymes administered intravenously, orally or intramuscularly decrease toxicity increase specificity of drug uptake enable slow release Physical Pharmacy 2

PROBLEMS WITH PHOSPHOLIPIDS phospholipids undergo oxidative degradation handling & storage must be under nitrogen expensive Physical Pharmacy 2

NIOSOMES Non-ionic + cholesterol -> NIOSOMES These vesicles prolong the circulation of entrapped drug Properties depend on Composition of bilayer Method of production e.g. cholesterol & single alkyl-chain non-ionic surfactant with a glyceril head group Physical Pharmacy 2

EXAMPLES OF NIOSOME APPLICATIONS Ketoconazole niosomes prepared using surfactant (Tween 40 or 80), cholesterol Satturwar PM; Fulzele SV; Nande VS; Khandare, JN Indian Journal of Pharmaceutical Sciences. 2002 Mar-Apr; 64(2): 155-8 Bovine serum albumin (BSA)loaded niosomes - Topical immunisation composed of sorbitan monostearate/sorbitan trioleate (Span 60/Span 85), cholesterol and stearylamine as constitutive lipids Sanyog Jain, S. P. Vyas, Journal of Pharmacy and Pharmacology Vol. 57, No. 9, pages 1177 (2005) Physical Pharmacy 2

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 Physical Pharmacy 2