Concept of Zeta Potential

By
Mr.Nitin H.Sonar
M. Pharm. (1st Sem.)
Concept of Zeta Potential
Dept. of Pharmaceutics
R. C. Patel Institutes of Pharmaceutical Education and Research, Shirpur 425 405
2015-16

Content
 Introduction.
 Definition.
 Factor Affecting.
 Measurement.
 DLVO Theory.
 Applications.
 Conclusion.
 References.
2

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.
3

Definition
• Zeta potential: It is the potential
observed at the shear plane.
• Zeta potential or electro-kinetic
potential is defined as the difference
in the potential between shear plane
and electro-neutral region of motion
the solution.
4

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.
5

Factors affecting zeta potential
1. pH : In aqueous media, the pH of the
sample is one of the most important
factors 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 important from a practical
consideration.
6

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...
7

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.
8

• 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...
9

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.
10

2. Electroacoustic phenomena: The electroacoustic technique characterizes
the dynamic 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
magnitude and phase angle. The sound wave is detected and analysed to
determine the motion of the particles.
11

Instrumentation
1. LASER
2. Cell
3. Detector
4. Digital signal Processor
5. Attenuator
12

1. Light Amplification by Stimulated Emission Radiation ( LASER ):
a. 632.8 nm Blue colour sample
b. 532 nm Red colour sample
13

Zeta potential Cell
a) Folded Capillary cell: (DTS1060)
solvent : water / alcohol
sample volume : 0.75 mL.
Body of cell : Polycarbonate
Electrodes : Gold plated copper
14

b) Universal Dip cell (ZEN1002):
Solvent: : Water / Alcohol
Sample Volume : approximately 0.7mL
3. Detector :
Avalanche Photodiode
15

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.
16

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
17

Conti...
b) Maintain solvent sheath around the particle:
The solvent layer prevent the particle coming closer and also
maintain Brownian motion
18

Applications
• Flocculate ( stick together )
• Suspension
• Emulsion
• Ceramics
• Waste water
19

Conclusion
• Zeta potential has long been recognized as excellent tool for
characterizing colloidal system.
• In recent years the concept of zeta potential has been applied to are
as 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 interdisciplinary basic research.
20

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
21

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
22

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