1. Electrostatic
Forcesby, FaNtasi’a
the forces between particles that are
caused by their electric charges.

2. • Van der Waals attractive force
• Electrostatic repulsive force
• Electrical double layer

3. COLLOID
• Colloidal particles often carry an electrical
charge and therefore attract or repel each
other.
• The charge of both the continuous and the
dispersed phase, as well as the mobility of the
phases are factors affecting this interaction.

4. Why Lemon Makes
Milk Curdle??

5. Electrostatic coating
• Painting industry
• principle :charge
powder particles
to similar polarity,
charged particles
repel each other,
forming a cloud
across the coating
area.

6. DLVO THEORY
• Boris Derjaguin
• Lev Landau
• Evert Verwey
• Theo Overbeek

7. VT = VA + VR + VS
• Where,
• VT = Total interaction force
• VA = van der Waals attraction
• VR = electrical double layer repulsive

8. • Two types of force in a stable colloid:
van der Waals' force
-attractive and binds particles together
electrostatic repulsion
-The total interaction potential can be calculated
as a function of distance, with colloid stability
being attained when two forces balance each
other.

9. Figure 1: Types of colloidal stabilization
• There are two fundamental mechanisms that
affect dispersion stability (figure 1):
Steric repulsion
Electrostatic or charge stabilization

10. Application of DLVO Theory
• Since 1940s, the DLVO theory has been used
to explain phenomena found in colloidal
science, adsorption and many other fields. Due
to the appearance of nanoparticles, DLVO
theory becomes even more popular. Because
it can be used to explain both general
nanoparticles such as fullerenes particles and
microorganisms.

11. ELECTROSTATIC DOUBLE LAYER:
DEFINITION
 A structure that appears on the surface of
an object when it is placed into a liquid
 Consists of two parallel layers of charge
surrounding the object
 The object might be a solid particle, a gas
bubble, a liquid droplet, or a porous body
 Important in determining the physical
properties of the system as a whole

12. FIRST LAYER SECOND LAYER
 The surface charge
(either positive or
negative)
 Comprises ions
adsorbed directly onto
the object due to a
host of chemical
interactions
 Is firmly adsorbed on
the surface of the
object
 Also called the diffuse
layer
 Composed of free ions
attracted to the surface
charge via the
Coulomb force
 Electrically screens the
first layer
 Is loosely associated
with the object
ELECTROSTATIC DOUBLE LAYER:

14. APPLICATION: ICE-CREAM

15. Zeta potential
• electrical potential that exists at the "shear
plane" of a particle, which is some small
distance from its surface.
• electric potential in the interfacial double
layer (DL) at the location of the slipping plane
versus a point in the bulk fluid away from the
interface
• charge that develops at the interface between
a solid surface and its liquid medium

16. • Zeta potential is considered to be the electric
potential of this inner area including this
conceptual sliding surface.

17. Zeta Potential (Smoluchowski’s Formula)
The Smoluchowski (for high ionic strengths) or Huckel
(for low ionic strengths) equations are used to obtain
the Zeta potential from the measured mobilities.

18. Zeta Potential vs. Surface Potential
The relationship between zeta potential and surface
potential depends on the level of ions in the
solution.

20. Zeta potential [mV] Stability behavior of the
colloid
from 0 to ±5 Rapid coagulation or
flocculation
from ±10 to ±30 Incipient instability
from ±30 to ±40 Moderate stability
from ±40 to ±60 Good stability
more than ±61 Excellent stability

21. • BIOMEDICAL
• EMULSIONS
• CLAY TECHNOLOGY:
(a) SOIL MECHANICS
(b) OIL WELL TECHNOLOGY
(c) CERAMICS
• WATER PURIFICATION AND INDUSTRIAL
WASTE
• MINERALS AND ORE FLOTATION
Zeta Potential Applications

22. Effect of ionic strength and
pH

23. Ionic stabilization…
• charged groups on the surface of the emulsion
droplets
will increase the repulsive forces
- Ionic emulsifier will form an electricity charge
double layer in the aqueous solution surrounding
each oil droplet.

24. • Ionic strength
effect???
- the thickness of the electrical double
layer
• Ionic strength
- electrical repulsion is greater than Van
der Waals attraction
Ionic stabilization…

25. • almost all food formulation will contain some
proteins
–proteins may be neutralpositively charged, or
negatively charged depending of the pH of the
system compared to their isoelectric point, pI
(pH < pI, positive charge; pH > pI, net negative charge).
• The charge on a droplet is important because it
determines the nature of its interactions with other
charged species.
Two droplets charges of opposite sign = attracted toward each other
two droplets charges of similar sign = repelled to each other

26. • properties of emulsions stabilized by;
-ionized emulsifiers
(pH and ionic strength of the aqueous phase)
• pH is adjusted
1. emulsifier loses its charge, or
2. if salt is added to “screen” the
electrostatic interactions between the
droplets
(repulsive forces may no longer be strong
enough to prevent the droplets from
aggregating)

27. Remember!!!
-the energy barrier modified by changing the pH
and pI
-effect directly the forces involved
• Increase pH above the isoelectric point (pI)
• the electrostatic interaction energy
• Decreasing ionic strength
-Increase energy barrier
-stabilizing the suspension
-increase turbidity

28. For example from our previous slide,
• The situation whereby ‘Why Lemon Makes Milk
Curdle??’
• decreases the pH of the emulsion toward the
isoelectric point of the proteins,
• thereby reducing the electrostatic repulsion
between the droplets and causing droplet
aggregation.

29. Prepared by;
FANTASIA