This document provides an overview of zeta potential, including: - Zeta potential is the electric potential at the boundary between the double layer and bulk solution surrounding charged particles suspended in a colloidal system. - Factors that affect zeta potential include pH, thickness of the double layer, and concentration of formulation components. - Zeta potential is important for predicting particle interactions and stability in colloidal systems based on DLVO theory of electrostatic repulsion and van der Waals attraction. - Measurement techniques include electrophoresis and electroacoustic methods to determine particle mobility from which zeta potential is calculated.

1. Zeta Potential
By
T.Dilip Kumar
Ms(Pharm.)Pharmaceutics
NIPER,Raebareli

2. Contents
• Introduction.
• Definitions.
• Factors affecting.
• Measurement.
• DLVO Theory.
• Importance .
• Case study.
• Conclusion.
• References.
2

3. 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 particles and has values that
typically range from +100 mV to
-100 mV.
3

4. Definitions
• Nernst potential: It is the potential of the solid surface itself
owing to the presence of potential determining ions.
• Nernst potential or electrothermodynamic potential is
defined as the difference in potential between the actual
surface and the electroneutral region of the solution.
• Zeta potential: It is the potential observed at the shear
plane.
4

5. Cont..
• Zeta potential or electrokinetic potential is defined as the
difference in the potential between shear plane and
electroneutral region of the solution.
• Zeta potential is more important than nernst potential
because the electrical double layer also moves, when the
particle is under motion.
5

6. 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 the
isoelectric point and is very important from a practical
consideration.
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. 6

7. Factors affecting
The higher the ionic strength, the more compressed the
double layer becomes. The valency of the ions will also
influence double layer thickness.
3. Concentration of a formulation component: The effect
of the concentration of a formulation component on the
zeta potential can give information to assist in formulating
a product to give maximum stability.
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8. Zeta Potential Measurement
• Zeta potential is not directly measurable, it can be calculated using
theoretical models like electrokinetic phenomena and electroacoustic
phenomena.
1. Electrokinetic :An important consequence of the existence of
electrical charges on the surface of particles is that they interact
with an applied electric field. These effects are collectively defined
as electrokinetic effects.
• Electrophoresis : 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. 8

9. Cont..
• The velocity is dependent on the strength of electric field
or voltage gradient, the dielectric constant of the medium,
the viscosity of the medium and 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
UE = 2 ε z f(κa)/3η
where UE = electrophoretic mobility, z = zeta potential,
ε =dielectricconstant, η = viscosity and f(κa) =Henry’s
function.
9

10. Cont..
• Electrophoretic light scattering: This method is most
popularly used to determine the velocity of the particles
suspended in a fluid medium under an applied electric field.
• The particles are irradiated with a laser light and the
scattered light emitted from the particles is detected.
• Since the frequency of the scattered light is shifted from
the incident light in proportion to the speed of the particles
movement, the electrophoretic mobility of the particles can
be measured from the frequency shift (Doppler shift) of the
scattered light.
10

11. Cont..
• 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

12. 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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13. Methods for stabilizing colloids
Stability can be obtained by surrounding colloidal particle with:
-an electrical double layer (electrostatic or charge stabilization).
-adsorbed or chemically attached polymeric molecules (steric
stabilization).
-free polymer in the dispersion medium (depletion stabilization).
•The stabilization due to the adsorbed layers on the dispersed
particle is generally called steric stabilization.
•Steric stabilization of colloidal particles is
achieved by attaching (grafting or
chemisorption) macromolecules to the
surfaces of the particles. 13

14. Cont..
The best steric stabilizers are amphiphilic 2-block or graft
copolymers.
Depletion stabilization of colloidal particles is imparted by
macromolecules that are free in solution.
The study of this type of stabilization is
still in its initial stage.
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15. Importance
• Zeta potential governs the degree of repulsion between
the adjacent ions of like charges. Hence it is used to
predict the particle-particle interaction
• Zeta potential can be used to predict the monodispersity
(or agglomeration) of particles.
• Zeta potential can be used to study nanoparticle-cell
interactions.
15

16. Case study
• Y. Zhang , C. S. Ozkan et.al demonstrated the use of
surface Zeta potential measurements as a new tool to
investigate the interactions of iron oxide nanoparticles
and cow pea mosaic virus (CPMV) nanoparticles with
human normal breast epithelial cells (MCF10A) and cancer
breast epithelial cells (MCF7).
• After MCF7 and MCF10A cells were incubated
respectively with two types of nanoparticles, the
significant differences in their surface charge change
indicate the potential role of Zeta potential.
16

17. Cont..
• 50 μg/ml iron oxide and CPMV nanoparticles were incubated
with MCF7 cancer breast epithelial cells and MCF10A normal
breast epithelial cells separately in 25 cm2 flask at 37°C in a
humidified and 5% CO2 atmosphere for specified time periods
of 30 min, 4 and 24h.
• After the incubation procedure, cells were washed with
Dulbecco’s Phosphate Buffered Saline (DPBS) for three times.
MCF10A cells were lifted off using Typsin-EDTA and MCF 7
cells were lifted off using Cell dissociation buffer. After that,
they were pelleted down and suspended into Hepes buffer for
Zeta potential measurements.
17

18. Cont..
time MCF10 A
incubated with
iron oxide
nanoparticles
MCF10 A
incubated with
CPMV
nanoparticles
MCF 7
incubated with
iron oxide
nanoparticles
MCF 7
incubated with
CPMV
nanoparticles
30min −30.47±0.15
mV
−29.93±0.88
mV
−25.17±0.52
mV
−24.51±0.73
mV
4hr −28.05±0.91
mV
−29.31±0.28
mV
−24.63±0.67
mV
−25.44±0.31
mV
24hr −27.05
mV±0.47
−25.49
mV±2.11
−26.55±0.78
mV
−26.29±
0.46 mV
ZETA POTENTIAL
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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
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 interdisciplinary basic research
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20. References
• CVS Subrahmanyam, Textbook of Physical Pharmaceutics.
Chapter 5: Interfacial phenomenon.2nd edition,2000.
Vallabh Prakashan publications, New Delhi.
• Yu Zhang et al., Zeta potential: a surface electrical
characteristic to probe the interaction of nanoparticles
with normal and cancer human breast epithelial cells,
Biomed Microdevices 2008; (10): 321–328.
• Soheyla Honary and Foruhe Zahir, Effect of Zeta
Potential on the Properties of Nano-Drug Delivery
Systems - A Review. Tropical Journal of Pharmaceutical
Research, April 2013; 12 (2): 255-264.
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21. THANK YOU
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