Zeta potential is a scientific term for electrokinetic potential (Zeta) in colloidal dispersions. • Electrokinetic potential refers to a potential difference in a liquid characterizing electrochemical equilibrium on interfaces. • Zeta potential is the charge that is located at the slipping point of a particle in the shear plane. • Zeta potential is the Colloidal chemistry. • It is usually denoted using the Greek letter zeta (ζ) hence ζ-potential. • (ζ), is the potential difference between the dispersion medium and the stationary layer of fluid attached to the dispersed particle. • Zeta Potential is the potential difference across an electrostatic double layer of ions that surround a solid particle dispersed in a polar liquid. In short, it is a measure of the surface charge of a particle. • 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

1. Undergraduate Course
Environmental Engineering Materials
(SEE-613) Theory
Course Instructor:
Engr. Shahbaz Hussain
Department of Structures and Environmental Engineering
University of Agriculture, Faisalabad-Pakistan

2. 2
Environmental Engineering Materials; SEE-613
12/24/2023
Nanomaterial; Zeta Potential

3. Historical Background
12/24/2023 Environmental Engineering Materials; SEE-613 3

4. What is Zeta Potential?
• Zeta potential is a scientific term for electrokinetic potential (Zeta) in colloidal
dispersions.
• Electrokinetic potential refers to a potential difference in a liquid characterizing
electrochemical equilibrium on interfaces.
• Zeta potential is the charge that is located at the slipping point of a particle in
the shear plane.
• Zeta potential is the Colloidal chemistry.
• It is usually denoted using the Greek letter zeta (ζ) hence ζ-potential.
• (ζ), is the potential difference between the dispersion medium and the stationary
layer of fluid attached to the dispersed particle.
• Zeta Potential is the potential difference across an electrostatic double layer of
ions that surround a solid particle dispersed in a polar liquid. In short, it is a
measure of the surface charge of a particle.
• 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.
12/24/2023 Environmental Engineering Materials; SEE-613 4

5. What is Zeta Potential?
• If the magnitude of Zeta potential is > 30
mV, then it is in stable suspension.
• The liquid layer surrounding the particle
exists as two parts; an inner region (Stern
layer) where the ions are strongly bound
and an outer (diffuse) region where they are
less firmly associated. Within the diffuse
layer there is a notional boundary inside
which the ions and particles form a stable
entity.
• When a particle moves (e.g. due to gravity),
ions within the boundary move it. Those
ions beyond the boundary stay with the bulk
dispersant. The potential at this boundary
(surface of hydrodynamic shear) is the zeta
potential.
12/24/2023 Environmental Engineering Materials; SEE-613 5
Schematic representation of zeta potential

6. What is Zeta Potential?
• Zeta potential is a physical
property which is exhibited
by any particle in
suspension,
macromolecule or material
surface.
• It can be used to optimize
the formulations of
suspensions, emulsions
and protein solutions,
predict interactions with
surfaces, and optimize the
formation of films and
coatings.
12/24/2023 Environmental Engineering Materials; SEE-613 6
Diagram demonstrating the potential difference
as a function of distance from the surface of a
particle in a dispersion medium

7. What is Zeta Potential?
12/24/2023 Environmental Engineering Materials; SEE-613 7
https://www.youtube.com/watch?v=NJJm_FVV8G0

8. How to measure Zeta-potential
12/24/2023 Environmental Engineering Materials; SEE-613 8
https://www.youtube.com/watch?v=GjpSvKHMPB0&t=18s

9. Colloid Science
• Three of the fundamental states of matter are
solids, liquids and gases. If one of these
states is finely dispersed in another then we
have a 'colloidal system'. These materials
have special properties that are of great
practical importance.
• There are various examples of colloidal
systems that include aerosols, emulsions,
colloidal suspensions and association
colloids.
12/24/2023 Environmental Engineering Materials; SEE-613 9

10. Colloid Science
12/24/2023 Environmental Engineering Materials; SEE-613 10

11. Colloid Science
• In certain circumstances, the particles in a dispersion
may adhere to one another and form aggregates of
successively increasing size, which may settle out
under the influence of gravity.
• An initially formed aggregate is called a floc and the
process of its formation flocculation. The floc may or
may not sediment or phase separate. If the aggregate
changes to a much denser form, it is said to undergo
coagulation.
• An aggregate usually separates out either by
sedimentation (if it is more dense than the medium) or
by creaming (if it less dense than the medium). The
terms flocculation and coagulation have often been
used interchangeably.
12/24/2023 Environmental Engineering Materials; SEE-613 11

12. Colloid Science
• Usually, coagulation is
irreversible whereas
flocculation can be
reversed by the process
of deflocculation.
• Figure 1 schematically
represents some of
these processes.
12/24/2023 Environmental Engineering Materials; SEE-613 12
Figure 1: Schematic diagram showing various
mechanisms where stability may be lost in a colloidal dispersion

13. 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.
• Imagine a particle in suspension with a negative zeta potential.
If more alkali is added to this suspension then the particles
tend to acquire more negative charge.
• If acid is added to this suspension then a point will be reached
where the charge will be neutralized.
• Further addition of acid may cause a build up of positive
charge if the ions are specifically adsorbed. In this case a zeta
potential versus pH curve will be positive at low pH and lower
or negative at high pH.
• The point where the plot passes through zero zeta potential is
called the isoelectric point and is very important from a
practical consideration. It is normally the point where
aggregation is most likely and hence the colloidal system is
least stable.
12/24/2023 Environmental Engineering Materials; SEE-613 13

14. Factors Affecting Zeta Potential
A typical plot of zeta potential versus pH is shown in figure. In this
example, the isoelectric point of the sample is at approximately
pH 5.5. In addition, the plot can be used to predict that the
sample should be stable at pH values less than 4 (sufficient
positive charge is present) and greater than pH 7.5 (sufficient
negative charge is present). Problems with dispersion stability
would be expected at pH values between 4 and 7.5 as the zeta
potential values are between +30 and -30mV.
12/24/2023 Environmental Engineering Materials; SEE-613 14
Typical plot of zeta potential versus pH showing the position of the isoelectric point and the pH
values in the green sectors where the dispersion would be expected to be stable

15. Factors Affecting Zeta Potential
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.
12/24/2023 Environmental Engineering Materials; SEE-613 15

16. Factors Affecting Zeta Potential
3. Conductivity
• The thickness of the double layer (K-1) 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. A
trivalent ion such as Al+3 will compress the double layer to a greater
extent in comparison with a monovalent ion such as Na+.
• Inorganic ions can interact with charged surfaces in one of two
distinct ways
i. Non-specific ion adsorption, where they have no effect on the
isoelectric point.
ii. Specific ion adsorption, which will lead to a change in the
value of the isoelectric point.
– The specific adsorption of ions onto a particle surface, even at low
concentrations, can have a dramatic effect on the zeta potential of
the particle dispersion.
– In some cases, specific ion adsorption can lead to charge reversal
of the surface.
12/24/2023 Environmental Engineering Materials; SEE-613 16

17. Factors Affecting Zeta Potential
4. 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. The
influence of known contaminants on the zeta potential of a
sample can be a powerful tool in formulating the product to
resist flocculation for example.
1. Electrokinetic Effects: 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.
There are four distinct effects depending on the way in
which the motion is induced. These are:
12/24/2023 Environmental Engineering Materials; SEE-613 17

18. Factors Affecting Zeta Potential
i. Electrophoresis: the movement of a charged particle
relative to the liquid it is suspended in under the
influence of an applied electric field
ii. Electroosmosis: the movement of a liquid relative to a
stationary charged surface under the influence of an
electric field
iii. Streaming potential: the electric field generated when
a liquid is forced to flow past a stationary charged
surface
iv. Sedimentation potential: the electric field generated
when charged particles sediment
12/24/2023 Environmental Engineering Materials; SEE-613 18

19. Factors Affecting Zeta Potential
2. Electrophoresis: When an electric field is applied across an
electrolyte, charged particles suspended in the electrolyte are attracted
towards the electrode of opposite charge.
• Viscous forces acting on the particles tend to oppose this movement.
When equilibrium is reached between these two opposing forces, the
particles move with constant velocity.
• 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.
e =
2 εζf(κa)
3η
Where,
e = Electrophoretic mobility,
ζ = Zeta potential,
ε = Dielectric constant,
η = Viscosity and
f(κa) = Henry’s function
12/24/2023 Environmental Engineering Materials; SEE-613 19

20. Zeta Potential Calculations
12/24/2023 Environmental Engineering Materials; SEE-613 20
• Permittivity (r) relative to a vacuum for water
• Permittivity (0) of free space, that is vacuum
f(ka) = 1
e =
2 εζf(κa)
3η
=
2 εζ  1
3η
e =
2 εζf
3η
 = or
f(ka) = 1.5 =
3
2
e =
2 εζf(κa)
3η
=
2 εζ  3
3η  2
e =
εζf
η
 = or

21. Zeta Potential Calculations
12/24/2023 Environmental Engineering Materials; SEE-613 21

22. Zeta Potential Calculations
12/24/2023 Environmental Engineering Materials; SEE-613 22

23. Zeta Potential Calculations
• Zeta potential is related to the electrophoretic mobility by the
Henry equation:-
ζ =
4ηf(κa)

 e
Electrophoretic migration is captured for each single particle
The electrophoretic mobility of charged colloids corresponds to the ratio
between their velocity, v, and the intensity of the electric field, E, under
which they migrate.
Where,
e = Electrophoretic mobility (μm·cm / V·s) , e =
V
E
ζ = Zeta potential (V),
ε = Dielectric constant, farad per meter (F/m)
η = Viscosity of medium, Pascal-second (Pa.s) or N.sm-2
v = Velocity of particle in E-field μm/s
E = Electric field strength (V/m)
f(κa) = Henry’s function or constant
12/24/2023 Environmental Engineering Materials; SEE-613 23

24. Zeta Potential Calculations
The units of κ, termed the Debye length, are reciprocal length and
κ-1 is often taken as a measure of the "thickness" of the electrical
double layer. The parameter 'a’ refers to the radius of the particle
and therefore κa measures the ratio of the particle radius to
electrical double layer thickness (figure). Electrophoretic
determinations of zeta potential are most commonly made in
aqueous media and moderate
12/24/2023 Environmental Engineering Materials; SEE-613 24

25. Numerical
Q. Under potential gradient of 3.5 volt/cm, a particle
suspended in water was found to move with a velocity of 1 
10-3 cm/sec. The medium has viscosity coefficient of 9  10-3
dyn-sec/cm2 and dielectric constant of 78. Calculate the zeta
potential of the particle. (300)2 is a conversion factor to volt
Sol:
12/24/2023 Environmental Engineering Materials; SEE-613 25

26. Numerical Assignment
12/24/2023 Environmental Engineering Materials; SEE-613 26
Question:
In water treatment processes, zeta potential is used
as an indicator of the effective coagulation of particles.
Given that a particle has an electrophoretic mobility of 0.5
gm. S-1 /volt.cm-1 at 25 o C, calculate the zeta potential of
the particle.
Assume that:
Viscosity () of water = 8.90 x 10-4 Pa.s
Permittivity (r) relative to a vacuum for water is 78.54
Permittivity (0) of free space, that is vacuum, is 8.854188 x
10-12 N/V2
f(κa) = 4
Ans: ζ = 7.64 102 V

27. Numerical Assignment Solution

28. Practice Problems
12/24/2023 Environmental Engineering Materials; SEE-613 28

29. Practice Problems
12/24/2023 Environmental Engineering Materials; SEE-613 29

30. Instrumentation
12/24/2023 Environmental Engineering Materials; SEE-613 30
1.Laser
2.Cell
3.Detector
4.Digital signal Processor
5.Computer
6.Attenuator
7.Compensation optics

31. Instrumentation
12/24/2023 Environmental Engineering Materials; SEE-613 31
A zeta potential measurement system comprises of six
main components (figure).
Firstly, a laser is used to provides a light source to
illuminate the particles within the sample. For zeta potential
measurements, this light source is split to provide an
incident and reference beam. The incident laser beam
passes through the center of the sample cell, and the
scattered light at an angle of about 13o is detected. When
an electric field is applied to the cell, any particles moving
through the measurement volume will cause the intensity of
light detected to fluctuate with a frequency proportional to
the particle speed and this information is passed to a digital
signal processor and then to a computer.

32. Instrumentation
12/24/2023 Environmental Engineering Materials; SEE-613 32
The Zetasizer Nano software produces a frequency
spectrum from which the electrophoretic mobility and hence
zeta potential is calculated. The intensity of the detected,
scattered light must be within a specific range for the
detector to successfully measure it. This is achieved using
an attenuator, which adjusts the intensity of the light
reaching the sample and hence the intensity of the
scattering. To correct for any differences in the cell wall
thickness and dispersant refraction, compensation optics
are installed to maintain optimum alignment.

33. Experimental Method
12/24/2023 Environmental Engineering Materials; SEE-613 33

34. DLVO Theory
12/24/2023 Environmental Engineering Materials; SEE-613 34
• 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.

35. DLVO Theory
12/24/2023 Environmental Engineering Materials; SEE-613 35
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

36. DLVO Theory
12/24/2023 Environmental Engineering Materials; SEE-613 36
b) Maintain solvent sheath around the
particle: The solvent layer prevent the
particle coming closer and also maintain
Brownian motion.

37. Applications
12/24/2023 Environmental Engineering Materials; SEE-613 37
➢ Coagulation and Flocculation: Zeta potential is used to
optimize the coagulation and flocculation processes in water
treatment. By understanding the surface charge of particles in
water, engineers can determine the most effective coagulants
and flocculants to destabilize particles and facilitate their
removal through sedimentation or filtration.
➢ Colloid Stability: Zeta potential is a crucial parameter in
assessing the stability of colloidal suspensions in water. It
helps in predicting the potential for particle aggregation or
dispersion. Controlling the zeta potential can be important in
preventing the formation of stable colloidal particles that might
be challenging to remove in water treatment processes.
➢ Electrokinetic Remediation: In soil and groundwater
remediation, electrokinetic processes are sometimes used to
mobilize and remove contaminants. Zeta potential
measurements help in understanding the electrokinetic
behavior of particles in the soil, aiding in the design and
optimization of electrokinetic remediation techniques.

38. Applications
12/24/2023 Environmental Engineering Materials; SEE-613 38
➢ Adsorption Processes: Zeta potential is relevant in adsorption
processes where contaminants are removed by adhering to
surfaces. Understanding the zeta potential of both the
contaminants and the adsorbent materials helps in designing
effective adsorption systems for water and wastewater
treatment.
➢ Membrane Filtration: Zeta potential plays a role in membrane
fouling, which is a common issue in membrane filtration
processes. By understanding the electrostatic interactions
between particles and the membrane surface, engineers can
optimize membrane materials and operating conditions to
minimize fouling and improve the efficiency of the filtration
process.
➢ Particle Transport in Porous Media: Zeta potential is
considered in modeling the transport of particles in porous
media. This is relevant in understanding the fate and transport
of contaminants in soil and groundwater and can inform
remediation strategies.

39. Applications
12/24/2023 Environmental Engineering Materials; SEE-613 39
Ceramic filter-Virus removal

40. Applications
12/24/2023 Environmental Engineering Materials; SEE-613 40
Cosmetics

41. Applications
12/24/2023 Environmental Engineering Materials; SEE-613 41
Detergency

42. Video 1
12/24/2023 Environmental Engineering Materials; SEE-613 42

43. Video 2
12/24/2023 Environmental Engineering Materials; SEE-613 43

44. Video 3
12/24/2023 Environmental Engineering Materials; SEE-613 44

45. Video 4
12/24/2023 Environmental Engineering Materials; SEE-613 45

46. Video 5
12/24/2023 Environmental Engineering Materials; SEE-613 46

47. Video 6
12/24/2023 Environmental Engineering Materials; SEE-613 47

48. 48
QUESTIONS???
12/24/2023 Environmental Engineering Materials; SEE-613