ByMr.Nitin H.Sonar

M. Pharm. (1st Sem.)

Concept of Zeta Potential

Dept. of PharmaceuticsR. C. Patel Institutes of Pharmaceutical Education and Research, Shirpur 425 405

2015-16

2

Content Introduction.

Definition.

Factor Affecting.

Measurement.

DLVO Theory.

Applications.

Conclusion.

References.

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Introduction

• Zeta potential is a scientific term for electrokinetic potential in colloidal dispersions.

• It is usually denoted using the Greek letter zeta (ζ), hence ζ - potential.

• The electric potential at the boundary of the double layer is known as the Zeta potential of the this particles and has values that typically range from +100 mV to -100 mV.

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Definition

• Zeta potential: It is the potential ob-

served at the shear plane.

• Zeta potential or electro-kinetic po-

tential is defined as the difference in the

potential between shear plane and elec-

tro-neutral region of motion the solution.

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Conti...

• Zeta potential is more important than Nernst potential because the

electrical double layer also moves, when the particle is under motion.

• Nernst potential: It is the potential of the solid surface itself owing to

the presence of potential determining ions.

• Nernst potential or electro thermodynamic potential is defined as

the difference in potential between the actual surface and the

electroneutral region of the solution.

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Factors affecting zeta potential1. pH : In aqueous media, the pH of the

sample is one of the most important fac-

tors that affects its zeta potential.

zeta potential versus pH curve will be

positive at low pH and negative at high pH.

There may be a point where the plot

passes through zero zeta potential.This point

is called isoelectric point and is very impor-

tant from a practical consideration.

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2. Thickness of double layer: The thickness of the double layer

depends upon the concentration of ions in solution and can be

calculated from the ionic strength of the medium.

• The higher the ionic strength, the more compressed the double layer

becomes. The valency of the ions will also influence double layer

thickness.

Conti...

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Zeta Potential Measurement

• Zeta potential is not directly measurable, it can be calculated using

theoretical models like electrokinetic phenomena and electroacoustic

phenomena.1. Electrokinetic Phenomena:a. Electrophoresis: The movement of charged particle relative to the liquid it is suspended

in under the influence of an electric field.

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• Zeta potential of dispersion is measured by applying an electric field

across the dispersion. Particles within the dispersion with a zeta

potential will migrate towards the electrode of opposite charge with

a velocity proportional to the magnitude of the zeta potential.

• The velocity of a particle in a unit electric field is referred to as its

electrophoretic mobility. Zeta potential is related to the

electrophoretic mobility by the Henry equation

Conti...

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Henry equation

UE = 2 ε z f(κa)/3η

Where:

UE = electrophoretic mobility,

z = zeta potential,

ε = dielectric constant,

η = viscosity

f(κa) = Henry’s function.

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2. Electroacoustic phenomena: The electroacoustic technique characterizes the dy-

namic mobility of particles in colloidal systems.

• In this method, a high frequency electric field is applied to the samples, causing

charged particles to oscillate, and to produce a sound wave of the same frequency.

• The oscillation (dynamic mobility) of the particles is described by its magni-

tude and phase angle. The sound wave is detected and analysed to determine the

motion of the particles.

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Instrumentation

1. LASER

2. Cell

3. Detector

4. Digital signal Processor

5. Attenuator

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1. Light Amplification by Stimulated Emission Radiation ( LASER ): a. 632.8 nm Blue colour sampleb. 532 nm Red colour sample

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Zeta potential Cell

a) Folded Capillary cell: (DTS1060)

solvent : water / alcohol sample volume : 0.75 mL. Body of cell : Polycarbonate Electrodes : Gold plated copper

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b) Universal Dip cell (ZEN1002):

Solvent: : Water / Alcohol Sample Volume : approximately 0.7mL

3. Detector : Avalanche Photodiode

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DLVO Theory

• The scientists Derjaguin, Landau, Verwey and Overbeek developed a theory in

the 1940s which dealt with the stability of colloidal systems.

• DVLO theory suggests that, the stability of a colloidal system is determined by

the sum of the Vander Waals attractive (VA) and electrical double layer repulsive

(VR) forces that exist between particles as they approach each other due to the

Brownian motion they are undergoing.

• The Vander waal forces depend on chemical nature and size of particle. The

electrostatic repulsive forces depend on density, surface charge and thickness of

double layer.

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Methods for stabilizing colloids Physical Stability can be achieved by maintaining the particle in

Brownian motion a) Provide Electric charge on surface of dispersed particle: The like charge on the particles will prevent these coming closer

together and thus maintaining a Brownian motion

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Conti...

b) Maintain solvent sheath around the particle: The solvent layer prevent the particle coming closer and also

maintain Brownian motion

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Applications

• Flocculate ( stick together )

• Suspension

• Emulsion

• Ceramics

• Waste water

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Conclusion

• Zeta potential has long been recognized as excellent tool for character-

izing colloidal system.

• In recent years the concept of zeta potential has been applied to areas beyond

classical colloidal sciences and industrial process.

• The expanding role of zeta potential in pharmaceutical sciences is attributable

to the advance in modern instrument of zeta potential measurement, the rapid

development of colloidal drug delivery system and emphasis on interdis-

ciplinary basic research.

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References:

1. CVS Subrahmanyam,(2000)Textbook of Physical Pharmaceutics, 2nd

edition. New Delhi, Vallabh Prakashan publications. page. No.172,356

2. L.chia; li,Y.tian,(2012) Encyclopedia of Pharmaceutical Technology, 2nd

edition.Volume-3.Marcel Dekker Series,page.No.3020-3031.

3. Partick j. Sinko,(2006)Martin’s Physical Pharmacy and Pharmaceutical

Science, 5th edition. Delhi, B.I.Publication PVT.LTD. Page.no.466

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Conti...

4. Dr. Shyamala Bhaskaran (2007)Physical Pharmacy, 1st edition.

Delhi, Birala Publication PVT. LTD. page.No.144

5. Alferd Martin (1991)Physical Pharmacy Indian edition. Bombay,

Varghese Publication House. page. No.482

6. Malvern (2010) User Manual of Zetasizer Nano, MANO317-5.0,

United Kingdom. page.No.15.1-15.12