1. Surfactants Introduction to Liquid Crystals
Kausar Ahmad

2. CONTENTS Properties of liquid crystals Types of liquid crystals
Thermotropic
Lyotropic
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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 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
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4. STATES OF MATTER Matter can exist in other states
Common states: solid, liquid, gas
Matter can exist in other states
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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
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6. 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
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7. 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
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8. TYPES OF LC
THERMOTROPIC
LYOTROPIC
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9. 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.
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10. PROPERTIES OF LC MOLECULES
Substances with molecules that are
ELONGATED
HAVING SOME DEGREE OF RIGIDITY.
"Cholesteryl benzoate". Licensed under Public Domain via Commons -
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11. 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
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12. 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
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13. 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
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14. 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
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15. 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)
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16. http://plc.cwru.edu/tutorial/enhanced/lab/lab.htm Click link
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17. 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
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18. STRUCTURAL CHANGES FOR LYOTROPIC LC
Formation of MICROEMULSION
Temperature
WATER
Inverse phases:
Inverse cubic
Inverse hexagonal
lamellar
hexagonal
OIL
cubic
micelles
Concentration of surfactant
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19. 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
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20. 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.
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21. Phospholipids/lecithin + H2O
SURFACTANT VESICLES
phospholipid/liposome
Phospholipids/lecithin + H2O
tve charge liposome (carriers for DNA)
Liposomes +
stearylamine
- ve charge liposome
dicetyl phosphate
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22. APPLICATION OF LIPOSOMES
can encapsulate:
drugs, proteins, enzymes
administered intravenously, orally or intramuscularly
decrease toxicity
increase specificity of drug uptake
enable slow release
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23. PROBLEMS WITH PHOSPHOLIPIDS
phospholipids undergo oxidative degradation
handling & storage must be under nitrogen
expensive
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24. 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
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25. 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 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)
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26. REFERENCES http://www.lci.kent.edu/lc.html#Description
(carbohydrate liquid crystal)
(niosomes)
Kreuter, J. (ed.) (1994). Colloidal Drug Delivery Systems. New York: Marcel Dekker, Chapter 3 & 4
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