phm2213 surf act ant liquid crystal

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PHM2213 Physical Pharmacy 2, 2006/7PHM2213 Physical Pharmacy 2, 2006/7 11

Surfactants

Introduction to Liquid Crystals

Kausar AhmadKausar Ahmad

Kulliyyah of PharmacyKulliyyah of Pharmacy


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ContentsContents

Properties of liquidProperties of liquid

crystalscrystals

Types of liquid crystalsTypes of liquid crystals

ThermotropicThermotropic

nematicnematic

smecticsmectic

cholestericcholesteric

LyotropicLyotropic

structuresstructures

applicationapplication

NIOSOMESNIOSOMES


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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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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


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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 crystalphase at a certain temperature are molecules that are

ELONGATED & have some degree of RIGIDITY. Try

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Properties of liquid crystals


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Typical chemical structures

cholesterol ester

phenyl benzoates

surfactants such aspolyethylene-oxides,alkali soaps, ammoniumsalts, 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 smecticA, where there

is layer-like arrangement as well as translational and

rotational motion of the molecules.

A further increase in temperature leads to the nematicphase, 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 anematic liquid crystal

i.e. long-range

orientational orderbut no positionalorder

The preferred direction

is known as director


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NematicNematic

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 cholestericdepends on the PITCH, the

distance over which thedirector makes onecomplete 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 themselvesapprox. parallel & tend to arrange

in layers

Not all positional order is

destroyed when a crystal meltsto 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 electro-

optical behaviour E.g. Kevlar aramid fibre bullet-proof vest &

airplane bodies (aromatic polyamide)


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Examples of phase changes

Cholesteryl myristate

solid smectic A

71C

cholesteric isotropic

79C 85C

4, 4-di-heptyloxyazoxybenxene

solid 74C 94C 124Csmectic C nematic isotropic


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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


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Structure formation in surfactant solution

micelle rod hexagonal

monolayer

bilayerReverse micelle

Formation of MICROEMULSION

REVERSE

HEXAGONAL

Oil/alcohol


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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 membranesspontaneously 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

[A]Anionic

e.g. alkane sulfonates

[B] Cationic

e.g. hexadecyl trimethyl ammonium bromide

[C]Amphoterice.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-(CH2CH2O) m H

m: 2-20, R : mixed; alkyl group C8C18


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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

Niosomes


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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 Jain1, S. P. Vyas2, Journal of Pharmacy and Pharmacology Vol.57, No. 9, pages 1177 (2005)


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References

1. http://www.lci.kent.edu/lc.html#Description

2. http://liqcryst.chemie.uni-hamburg.de/lc_lc.php

3. http://www.glycoprojects.kimia.um.edu.my/website/Glyco/

(carbohydrate liquid crystal)

4. http://www.gla.ac.uk/~jmb17n/conacher.pdf(niosomes)

5. http://plc.cwru.edu/tutorial/enhanced/files/lc/phase/phase.ht

m

6. J Kreuter (ed.), Colloidal Drug Delivery Systems, Marcel

Dekker, New York (1994) Chapter 3&4


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http://plc.cwru.edu

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