It is the electrokinetic potential in colloidal dispersions. Zeta potential is the potential difference between the dispersion medium and the stationary layer of fluid attached to the dispersed particle. When a colloidal suspension is placed in an electrical field, the colloidal particles move in one direction (toward the positive pole). The counter ions move is another direction (toward the negative pole). The electric potential developed at the solid liquid interface is called Zeta (ζ )potential. Zeta potential is not equal to surface potential. Zeta potential is less than electro chemical potential. Increasing the concentration of electrolytes in the solution results in the decrease in thickness of double layer. Thickness is also influenced by increasing valency of ions. Isoelectric point: At this point electrolyte concentration is maximum, thickness of double layer becomes neligible . Particle replusive force minimum. Zeta potential is equal to zero.

1. Zeta potential
Presented by
Chitra Devi A
M.Sc. (Ag.) Soil science
TNAU, COIMBATORE

2. Diffuse double layer
 The surface of all dispersed particles surrounded by a thin layer of ions that
have the opposite charge of the particle’s surface called the Stern layer.
 Further from the surface is an additional layer of more loosely-associated ions
of opposite charge to the surface that move with the particle as it travels
through a medium due to Brownian motion or sedimentation is called the
double layer.
 Zeta potential is a physical property exhibited by all solid-liquid and liquid-liquid
colloidal systems.

3. Diffuse double layer

4. Zeta potential
 It is the electrokinetic potential in colloidal dispersions.
 Zeta potential is the potential difference between the dispersion medium and the
stationary layer of fluid attached to the dispersed particle.
 When a colloidal suspension is placed in an electrical field, the colloidal particles move in
one direction (toward the positive pole).
 The counter ions move is another direction (toward the negative pole).
 The electric potential developed at the solid liquid interface is called Zeta (ζ )potential.
 Zeta potential is not equal to surface potential.
 Zeta potential is less than electro chemical potential.

5. 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(equilibrium
condition) of the solution.
Zeta potential:
• It is the potential observed at the shear plane.
• 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.

6. Effect of electrolytes on zeta potential
 Increasing the concentration of electrolytes in the solution results in the
decrease in thickness of double layer.
 Thickness is also influenced by increasing valency of ions.
Isoelectric point:
At this point electrolyte concentration is maximum, thickness of double
layer becomes neligible . Particle replusive force minimum. Zeta potential is equal
to zero.

7. Electrophorosis
 It is determined from the electrophoretic mobility of the suspension using ,
Ve – electrokinetic velocity
D – dielectric constant
ζ -zeta potential
E – applied emf
η –viscosity of the fluid
Ve = Dζ E / 4πη

8. Factors affecting Zeta Potential:
pH : Due to decrease in pH the zeta potential can be reduced resulting from the
reduction of negative charge on the clay micelle and also from the replacement of
sodium or other monovalent ions with hydrogen (H+) ion.
Valency of ion : Divalent (Ca2+, Mg2+) or trivalent (Al3+) can be introduced to exchange
with the monovalent cations and reduces the zeta potential and thereby accelerates the
phenomenon of flocculation.
Concentration of cation : By the addition of simple salts the concentration of cations
will increase around the clay particles and thereby causes flocculation by reducing the
zeta potential.

9. Dispersion:
 When the dilute colloidal particles (suspended in water) tend to repel each
other, allowing each particle to act completely independent of the others. This is
known as the dispersion
 Dispersion is encouraged by higher pH values, where the zeta potential is at a
maximum.
 Highly hydrated monovalent cations like Na+ stabilize the dispersed colloids.
 So the conditions for causing dispersion are high hydration, low electrolyte
content, a pH far from isoelectric point and absence of opposite charge colloids.

10. Hydration
 The sodium-saturated colloidal clay hydrolyzes to form NaOH and
Na2CO3 and is highly dispersed, highly hydrated.
 The sodium-saturated colloidal clay particles will able to move easily
in an electrical field than that of Ca-saturated clay.

11. Flocculation
 Flocculation process is the opposite of dispersion that means colloidal particles
tend to attract each other and coagulate like a bigger particle caused by a decrease
in zeta potential and hydration.
 The condition of flocculation is generally beneficial in the formation of good soil
structure.
 The ability of common cation to flocculate soil colloids is in the order of
Al>Ca & H > Mg > K > Na
 Conditions favourable for flocculation are dehydration, a high electrolyte content,
a pH at the isoelectric point, and the presence of an oppositely charged colloid.

12.  When the zeta potential (double layer potential) is decreased below the
critical value, the repulsion between the approaching colloidal particles is
reduced to such an extent that those colliding with a certain velocity
forming flocules.
 This is the simple mechanism in the formation of flocules resulting from
the decrease of charge density or thickness of the double layer or both.

13. Stability behavior of the colloid particles
with respect to zeta potential
Zeta Potential (mV) Stability behavior of the particles
0 to ±5 Rapid Coagulation or Flocculation
±10 to ±30 Incipient Instability
±30 to ±40 Moderate Stability
±40 to ±60 Good Stability
More than ±61 Excellent Stability

14. Difference between zeta potential and point of zero
charge
Zeta potential Point of zero charge
It is the electrokinetic potential
of the colloidal dispersion
It is the pH at which the overall
charge of a particle is zero
It measures potential
difference in a diffuse double
layer
It measures the pH value