Transcript Liquid Crystals

Surfactants
Introduction to Liquid Crystals
Kausar Ahmad
Kulliyyah of Pharmacy
Contents

Properties of liquid
crystals

Lyotropic

structures

Types of liquid crystals

application

Thermotropic

NIOSOMES

nematic

smectic

cholesteric
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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
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STATES OF MATTER


Common states:

solid

liquid

gas
Matter can exist in
other states
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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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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
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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
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Typical chemical structures

cholesterol ester

phenyl benzoates

surfactants such as
polyethylene-oxides,
alkali soaps, ammonium
salts, lecithin

paraffins

glycolipids

cellulose derivatives
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Typical applications

LCD displays

dyes (cholesterics)

advanced materials (Kevlar)

membranes

temperature measurement (by changing colours)

solvents for GC, NMR, reactions, etc.
 Drug
delivery
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Types of liquid crystals
Thermotropic

Phase transition depends on temperature

Nematic

Smectic

Cholesteric
Lyotropic

Phase transition depends on temperature &
concentration
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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.
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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
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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
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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
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-

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
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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
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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 electrooptical behaviour

E.g. Kevlar aramid fibre – bullet-proof vest &
airplane bodies (aromatic polyamide)
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Examples of phase changes
Cholesteryl myristate
solid
71C
smectic A
79C
cholesteric
85C
isotropic
4, 4’-di-heptyloxyazoxybenxene
solid
74C
smectic C
94C
nematic
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124C
isotropic
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Thermotropic vs Lyotropic
LYOTROPIC
THERMOTROPIC




Absence of solvent
Rigid organic molecules
Depends on Temperature
Structures:
 Smectic
 Nematic
 Cholesteric


In solvent
Surfactants

Depends on Temperature,
Concentration, salt, alcohol

Structures:


Lamellar
Hexagonal etc
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Structure formation in surfactant solution
monolayer
micelle
Oil/alcohol
rod
hexagonal
REVERSE
HEXAGONAL
Reverse micelle
Formation of MICROEMULSION
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bilayer
20
Effect of temperature and concentration on the
structure of lyotropic liquid crystals
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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
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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.
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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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Problems with phospholipids

phospholipids undergo oxidative
degradation

handling & storage must be under nitrogen

expensive
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Formation of liquid crystals using surfactants
Anionic
e.g. alkane sulfonates
Cationic
e.g. hexadecyl trimethyl 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
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Niosomes

Non-ionic + cholesterol -> NIOSOMES

These vesicles prolong the circulation of entrapped
drug

Properties depend on
1.
Composition of bilayer
2.
Method of production
e.g. cholesterol & single alkyl-chain non-ionic
surfactant with a glyceril head group
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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 Jain, S. P. Vyas, Journal of Pharmacy and Pharmacology Vol. 57,
No. 9, pages 1177 (2005)
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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
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http://plc.cwru.edu/tutorial/enhanced/lab/lab.htm
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