PHM2213 Surfactant Liquid Crystal

Surfactants Introduction to Liquid Crystals:

PHM2213 Physical Pharmacy 2, 2006/7 1 Surfactants Introduction to Liquid Crystals Kausar Ahmad Kulliyyah of Pharmacy

Contents:

PHM2213 Physical Pharmacy 2, 2006/7 2 Contents Properties of liquid crystals Types of liquid crystals Thermotropic nematic smectic cholesteric Lyotropic structures application NIOSOMES

Synergistic Effects of Surfactants:

PHM2213 Physical Pharmacy 2, 2006/7 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

STATES OF MATTER :

PHM2213 Physical Pharmacy 2, 2006/7 4 STATES OF MATTER Common states: solid liquid gas Matter can exist in other states

LIQUID CRYSTALS:

PHM2213 Physical Pharmacy 2, 2006/7 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

Crystals vs Liquid Crystals:

PHM2213 Physical Pharmacy 2, 2006/7 6 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 Crystals vs Liquid Crystals

Properties of liquid crystals:

PHM2213 Physical Pharmacy 2, 2006/7 7 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 Properties of liquid crystals

Typical chemical structures:

PHM2213 Physical Pharmacy 2, 2006/7 8 Typical chemical structures cholesterol ester phenyl benzoates surfactants such as polyethylene-oxides, alkali soaps, ammonium salts, lecithin paraffins glycolipids cellulose derivatives

Typical applications:

PHM2213 Physical Pharmacy 2, 2006/7 9 Typical applications LCD displays dyes (cholesterics) advanced materials (Kevlar) membranes temperature measurement (by changing colours) solvents for GC, NMR, reactions, etc. Drug delivery

Types of liquid crystals:

PHM2213 Physical Pharmacy 2, 2006/7 10 Types of liquid crystals Thermotropic Phase transition depends on temperature Nematic Smectic Cholesteric Lyotropic Phase transition depends on temperature & concentration

As temperature increases…..:

PHM2213 Physical Pharmacy 2, 2006/7 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.

Nematic:

PHM2213 Physical Pharmacy 2, 2006/7 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

Nematic…:

PHM2213 Physical Pharmacy 2, 2006/7 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

Cholesteric:

PHM2213 Physical Pharmacy 2, 2006/7 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

Slide 15:

PHM2213 Physical Pharmacy 2, 2006/7 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

Smectic:

PHM2213 Physical Pharmacy 2, 2006/7 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

LIQUID CRYSTAL POLYMERS:

PHM2213 Physical Pharmacy 2, 2006/7 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)

Examples of phase changes:

Examples of phase changes Cholesteryl myristate solid smectic A 71C cholesteric isotropic 79C 85C 4, 4’-di-heptyloxyazoxybenxene solid 74C 94C 124C smectic C nematic isotropic

Thermotropic vs Lyotropic:

PHM2213 Physical Pharmacy 2, 2006/7 19 Thermotropic vs 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

Structure formation in surfactant solution:

PHM2213 Physical Pharmacy 2, 2006/7 20 Structure formation in surfactant solution micelle rod hexagonal monolayer bilayer Reverse micelle Formation of MICROEMULSION REVERSE HEXAGONAL Oil/alcohol

Effect of temperature and concentration on the structure of lyotropic liquid crystals:

PHM2213 Physical Pharmacy 2, 2006/7 21 Effect of temperature and concentration on the structure of lyotropic liquid crystals

SURFACTANT VESICLES:

PHM2213 Physical Pharmacy 2, 2006/7 22 SURFACTANT VESICLES [A] Phospholipids (e.g. lecithin) + H 2 O ----> phospholipid vesicles or liposomes [B] Liposomes + (long chain) stearylamine -------> tve charge liposome (carriers for DNA) [C] Liposomes + dicetyl phosphate -----  - ve charge liposome

Vesicles:

PHM2213 Physical Pharmacy 2, 2006/7 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.

Application of Liposomes:

PHM2213 Physical Pharmacy 2, 2006/7 24 Application of Liposomes can encapsulate : drugs , proteins, enzymes administered intravenously, orally or intramuscularly decrease toxicity increase specificity of drug uptake enable slow release

Problems with phospholipids:

PHM2213 Physical Pharmacy 2, 2006/7 25 Problems with phospholipids phospholipids undergo oxidative degradation handling & storage must be under nitrogen expensive

Formation of liquid crystals using surfactants:

PHM2213 Physical Pharmacy 2, 2006/7 26 Formation of liquid crystals using surfactants [A] Anionic e.g. alkane sulfonates [B] Cationic e.g. hexadecyl trimethyl ammonium bromide [C] Amphoteric e.g. alkyl betaines Due to toxicity of ionic surfactants, the vesicles are not used for drug delivery [D] Non-ionic e.g. alcohol ethoxylates R-O-(CH 2 CH 2 O) m H m: 2-20, R : mixed; alkyl group C 8 C18

Niosomes:

PHM2213 Physical Pharmacy 2, 2006/7 27 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 Niosomes

Examples of niosome applications:

PHM2213 Physical Pharmacy 2, 2006/7 28 Examples of niosome applications 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 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)

References:

PHM2213 Physical Pharmacy 2, 2006/7 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 J Kreuter (ed.), Colloidal Drug Delivery Systems, Marcel Dekker, New York (1994) Chapter 3&4

Slide 30:

PHM2213 Physical Pharmacy 2, 2006/7 30 http://plc.cwru.edu