Liquid crystalline system

Mr. Sagar Kishor SavaleMr. Sagar Kishor Savale[Department of Pharmaceutics][Department of Pharmaceutics]

[email protected]

mailto:[email protected]

CONTENT

1. Introduction

2 .What is Liquid crystal ?3. Classification of Liquid crystal

4.Method of characterization of LCs

5.Application of Liquid Crystal

6.Referances205/01/23Sagar Kishor Savale

Intermediate state of mesophases & halfway between isotropic liquid &solid crystal.

In solid crystal, basic unit display translational long range order, with center of molecule located on crystal lattice &display orientational order.

In isotropic liquid, basic unit do not preset positional or orientational long rang order.

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In plastic crystal ,located on lattice but without any orientational order.

In LCs,basic unit display orientational order & even positional order along same direction.

LCs,phases represent intermediate stages called mesophases. Molecule that form mesophases called mesogen.


Solid Phase Molecules with both orientation and positional

orders, and are held to each other strongly Liquid Phase Molecules with no orientation and positional orders,

but are held together by weak intermolecular forces Gas Phase No ordering, no intermolecular attraction


A fluid phase in which a liquid crystal flows and will take the shape of its container. It differs from liquid that there are still some orientational order possessed by the molecules.


Liquid Crystalline

Systems

Thermotropic Lyotropic

Nematic Smectic Cholesteric

Intrinsic Extrinsic

CLASSIFICATION:


1.THERMOTROPIC: Phase transition depend on temperature Temp increases, first LCs phase is smectic A

&layer like arrangement & rotational motion of molecule.

Further increase temp lead to nematic phase , molecule rapidly diffuse out of initial lattice structure & form layer like arrangement .

At highest Temp, material become isotropic liquid where motion of molecule changes again.


A)Nematic phase: Long range orientation order but no positional order.

Preferred direction is known as director.

Phase Structure change in number way e.g.. electric or magnetic field or treatment of surface of sample container.


B) Cholesteric/chiral nematic LCs : first LC through polarizing microscope is

cholesteryl benzoate.eg cholesteric LC at 147° c & isotropic 186° c.

It great potential uses following drug delivery, sensors, Thermometer, fashion fabrics that change color with Temp, display devices

In cholesteric phase, there is orientation order & no positional order, but director is in helical order.


Structure of this LC depend on pitch, which is distance over director makes one complete turn. one pitch comprises several hundred nanometer.

pitch affected by following :Temp, pressure, electric & magnetic field.


The director rotates about a horizontal axis. The distance for one full rotation is called a pitch.


Types of cholesteric LCs:I. Intrinsic cholesteric:

obtained by adding a chiral amphiphilic molecule to nematic lyotropic LC.

Molecule take part in micellar structure as nonchiral amphiphile.


al. Extrinsic cholesteric

obtained by adding a chiral nonamphiphilic molecule to nematic lyotropic.

Depending on electrostatic characteristics of molecule , it can accommodated either in inner or outer part of micelle.


C) SMECTIC PHASE: Occurs at temp below nematic or

cholesteric phase.

Not positional order are destroyed when crystal melts to form a smectic LC & these are useful in drug delivery.

Different smectic distinguished on basis of arrangements with varying temp.


Phase transitions occurs with increasing temp e.g.. crystalline to smectic C to smectic A to nematic to isotropic or crystalline to nematic to isotropic.

example of phase changes:

Solid 74˚c Smectic C 94˚c. Nematic 124˚c isotropic


Smectic A phase:Director perpendicular to the plane

Smectic C phase:director makes an angle with the plane


2)LYOTROPIC LIQUID CRYSTAL: Phase transition depend on Temp and Conc. When two different substances are mixed together,

the mixture can exhibit different phases not only as the temperature is changed, but also as the concentration of one component of the mixture is varied.

Example: a molecule that has end groups with different properties (one is hydrophobic and the other is hydrophilic).


Lyotropic liquid crystal differ from thermotropic LCs, form by mesogen and by associate hydrate and solvate molecule.

Hydration, solvation are rod shaped

molecule result in different geometries such as cone and cylinder.

Cylindrical arrange in layer, result in laminar

phase by altering polar, non polar layer.


Fig. 1)Cubic Lyotropic LCs 2) Lamellar Lyotropic LCs


Disc-like molecules The axis perpendicular to the molecules tends to

orient along a specific direction

nematicColumar discotic(smectic discotic)The molecules tend to position themselves in column 2405/01/23Sagar Kishor Savale

The molecule must be elongated in shape-length should be significantly greater than its width.

Molecule must have some rigidity in its central region.

The ends of the molecule are somewhat flexible.


1.TRANMISSION ELECTRON MICROSCOPY: Due to high magnification power electron

microscope , microstructure of LCs can be visualized.

Aqueous sample do not survive high vacuum of electron microscope with out loss of water & their microstructure changes.

Therefore special techniques of sample preparation necessary which is freeze fracture.


•

2. X RAY SCATTERING: Interfererences pattern arises due to

distances of Interlayer spacing “d”. Braggs equation ,d calculate :d=n( /2)sin Where d =wavelength of x ray. n=integer & denotes under of

Interference. =angle under which interference

occurs.

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Large ‘d’ in region of long range order are register by small angle x ray diffraction tech.

Small ‘d’ in region of short range order register by wide angle x ray diffraction tech.

SAXD important for exact ‘d’ determination.


3. RHEOLOGY: Different LCs are rheological prop. Which

increase in microstructure LCs, it’s consistency increases & flow become more viscous.

Low flow ability of lyotropic LCs such cubic, hexagonal due to 3&2 dimensional order.

Lamellar mesophases are one dimensional long range has high flowability due to gel character , cubic & hexagonal mesophases exhibit stress until flow occur .


4.DETECTION OF VESICLE SIZE BY LASER LIGHT SCATTERING:

Quick method ,applied for particle >1m.

Rayleigh's theory hold for particles <200nm , which consider scattering intensity to proportional to sixth potency of particle diameter.

Scattering intensity depends on scattering angle, absorption & size of particle as well as refractive indices of both particle & dispersion medium.


1) Liquid crystalline formulation for topical use: Amphilic excipient form lyotropic LCs, surfactant use as emulsifier which form micelles after dissolved in solvent ,conc. Increases form LCs.

2) Surfactant gel: Monophasic system of lyotropic LCs are

used limited to gel. High surfactant conc. form density

packed & identified as cubic LCs.


Gel agitated mechanically , elastic prop. Evident , because of resonance effect in audible range called as ‘ringing gels’.

Ringing gel used in topical NSAID formation.

3)Ointment & cream: Surfactant conc. In this lower than in gel. Ointment non a.q preparation & cream are ointment in

water added. microstructure of both consist of LCs & its network or matrix formed by amphiphilic molecule.


4) Liposome dispersions for installation into lung: Liposomal formation consist of surfactant, which

coats mucosa of bronchi & prevents collapse of alveolar of lung , has developed for patient suffer from infant respiratory distress syndrome.

5) Transdermal patch: Patch contain drug substance in reservoir form

which drug release controlled manner. This patch disadvantage are dose dumping

occur in membrane damage during handling.


LCs vehicle with lamellar structure used reservoir due to high solubilization capacity.

6) Sustained release form solid,semisolis and liquid formulation :

Sustained formulation it have developed reduce application frequency.

LCs excipient appropriate candidate because in LCs vehicle drug diffusion is reduced by factor of 10-1000 in comparison with liquid vehicle such as a solution


Semisolid formulation :o Solubilization of drug substance LCs

vehicles results in semisolid formulation which is used for topical application.

Solid formulation:o For the sustained drug release may contain

mesogenic polymer as excipient which form matrix, which usually compressed into tablet.


7) LCs in Cosmetics: LCs used for decorative purpose in

cosmetic

Cholesteric LCs suitable because of there iridescent color effect and find application for nail varnishes, eye shadow and lipstick.


Encyclopedia of pharnmaceutical technology, second edition Volume three, Edited by James Swarbrick, James C. Boylan page no. 834-851

Physical pharmacy fourth edition edited by Alfred Martin, Pilar Bustamante, page 36-37.

Bentelyes textbook of pharmaceutics forth edition edited by E.A.Rawlins page no.59-69.


The Cooper and Gunn’s “Dispensing Pharmacy”, 6th edition ,CBS publisher and distributors NEW DELHI,page no.126.


Liquid crystalline system

Health & Medicine

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