1. IMK209
PHYSICAL PROPERTIES OF FOOD
FOOD COLLOIDS
EMULSION & FOAM
HAZWA GROUP MEMBERS:
MOHAMAD ISWANDI B ISHAK (104434)
AISHAH BT MOHD MARSIN (104393)
SITI ZAINUN BT NASIR (104492)
NUR HANISAH BT ISMAIL (104450)
NUR AIN BT AB RAHMAN (104457)

2. TYPE OF
ELECTROSTATIC
(INTERACTIVE /
REPULSIVE) FORCE IN
COLLOIDAL PARTICLE

3.  The stability of particle dispersion will depend upon the
balance of the repulsive and attractive forces that exist
between particles as they approach one another.
 If all the particles have a mutual repulsion then the
dispersion will remain stable.
 However, if the particles have little or no repulsive force
then some instability mechanism will eventually take place
e.g. flocculation, aggregation.

4.  The zeta potential of a particle is the overall charge that the
particle acquires in a particular medium and can be measured
on a Zetasizer instrument.

5.  If all the particles in suspension have a large negative or
positive zeta potential then they will tend to repel each other
and there is no tendency for the particles to come together.
 If the particles have low zeta potential, the particles will come
together since values then there is no force to prevent the
particles together.
 The effect of the pH, concentration of an additive or the ionic
strength of the medium on the zeta potential can give
information in formulating the product to maximize stability.

6. There are two fundamental mechanisms that affect
dispersion stability :
Steric repulsion
this involves polymers added to the system adsorbing onto
the particle surface and preventing the particle surfaces
coming into close contact. If enough polymer adsorbs, the
thickness of the coating is sufficient to keep particles
separated by steric repulsions between the polymer layers,
and at those separations the Van der Waals forces are too
weak to cause the particles to adhere.
Electrostatic or charge stabilization
this is the effect on particle interaction due to the
distribution of charged species in the system.

8. DLVO Theory

9.  DLVO Theory named from 4 scientist that proposed this
theory on 1940s which are :
- Derjaguin.
- Landau.
- Verwey.
- Overbeek.
 DLVO theory suggests that the stability of a particle in
solution is dependent on its total potential energy.

10. VA = -A/(12 π D2
)
Potential Energy Due To The Van der Waals
Attractive Forces
A is the Hamaker constant.
D is the particle separation.
VR = 2 π ε a ξ2
exp(- κD)
Potential Energy Due To The Electrical Double Layer Repulsive
Forces
a is the particle radius.
π is the solvent permeability.
κ is a function of the ionic composition.
ξ is the zeta potential.
VT = VA + VR + VS
VS
Potential Energy Due To The Solvents

11.  The stability of a colloidal system is determined by the sum
of these van der Waals attractive force (VA) and electrical
double layer repulsive force (VR) that exist between particles
as they approach each other due to the Brownian motion
they are undergoing.
 DLVO Theory proposes that an energy barrier resulting
from the repulsive force function to prevent two particles
approaching one another and adhering together

12. Figure 1:
Schematic diagram of the variation of free energy with particle separation according to DLVO
theory. The net energy is given by the sum of the double layer repulsion force and the van der
Waals attractive force that the particles experience as they approach one another

13.  But if the particles collide with sufficient energy to
overcome that barrier, the attractive force will pull them
into contact where they adhere strongly and irreversibly
together.
 Therefore if the particles have a sufficiently high repulsion,
the dispersion will resist flocculation and the colloidal
system will be stable.
 However if a repulsion mechanisms does not exist then
flocculation will eventually take place.

14.  There is a possibility of a
“secondary minimum” where a much
weaker and potentially reversible adhesion
between particles exists together.
 These weak flocs are sufficiently stable not to be broken up
by Brownian motion, but may dissociate under an
externally applied force such as vigorous agitation.
In High Salt
Concentration
Situation

15. Figure 2:
Schematic diagram of the variation of free energy with particle separation at higher salt
concentrations showing the possibility of a secondary minimum.

16. ELECTRICAL
DOUBLE LAYER
(EDL)

17.  A double layer DL, also called an electrical double layer, EDL is a
structure that appears on the surface of an object when it is placed
into a liquid. The object might be a solid particle, a gas bubble, a
liquid droplet or a porous body.
OR
 The electrical double layer (EDL) is a structure which describes the
variation of electric potential near a surface, and has a significant
influence on the behavior of colloids and other surfaces in contact
with solution or solid-state fast ion conducter.

18. The DL refers to the layers of charge surrounding the object.
 Surface charge
- charged ions (commonly negative) adsorbed on the particle surface.
 Stern layer,SL (either positive or negative),
-comprises ions adsorbed directly onto the object due to a host of chemical
interactions.
-counterions (charged opposite to the surface charge) attracted to the particle surface
and closely attached to it by the electrostatic force.
 Diffuse layer.
- composed of ions attracted to the surface charge via the coulomb force, electrically
screening the first layer.
- loosely associated with the object, because it is made of free ions which move in the
fluid under the influence of electric attraction and thermal motion rather than
being firmly anchored.

20.  EDL is usually most apparent in systems with a large ratio of surface area to
volume, such as colloids or porous bodies with particles or pores
(respectively) on the scale of micrometers to nanometers.
 Colloidal particles gain negative electric charge when negatively charged ions
of the dispersion medium are adsorbed on the particles surface.
 A negatively charged particle attracts the positive counterions surrounding
the particle.
 Electric Double Layer is the layer surrounding a particle of the dispersed
phase and including the ions adsorbed on the particle surface and a film of
the countercharged dispersion medium.The Electric Double Layer is
electrically neutral.

22.  The electrical potential within the Electric Double Layer has the maximum value on the
particle surface (Stern layer). The potential drops with the increase of distance from the
surface and reaches 0 at the boundary of the Electric Double Layer.
 When a colloidal particle moves in the dispersion medium, a layer of the surrounding
liquid remains attached to the particle.
 The boundary of this layer is called slipping plane (shear plane).
 The value of the electric potential at the slipping plane is called Zeta potential, which is
very important parameter in the theory of interaction of colloidal particles.
 The EDL is sensitive to electrolyte and also temperature.
 This mean that the stability of the colloid may be manipulated by adding electrolites or
changing the temperature.

24. The following methods are used for the destabilization of the colloidal particles by
neutralization:
Addition of an electrolyte to the colloid.
- The colloidal particles are neutralized by the oppositely charged electrolyte
ions. The destabilization of an lyophobic colloid occurs at the electrolyte
concentrations exceeding the value of the critical coagulation concentration.
- The critical coagulation concentration is strongly dependent on the valence of
the electrolyte ions. The higher the valence the lower the critical concentration
of the electrolyte required for the coagulation of the colloid.

25. Addition of another colloid, particles of which are charged oppositely to the particles
of the first colloid.
- The oppositely charged particles of the colloids attract each
other and neutralize the electric charge.
-The best results of the destabilization by this method are
achieved when the second colloid is added at a concentration
precisely required for full neutralization.
-Too low and too high concentrations of the second colloid do
not result in complete destabilization.

26. ZETA
POTENTIAL

27. Figure 1: Schematic representation of zeta potential
What is Zeta Potential ?
Zeta potential is the electrical potential at the hydrodynamic
plane of shear.

28. Significant of Zeta Potential
• Zeta potential measurements can be used to predict dispersion stability.
• Particles interact according to the magnitude of the zeta potential, not their
surface charge.
• Zeta potential can determine the magnitude of the electrostatic interaction
between particles.
• It can be effected by small change in pH and ionic strength of the medium.
Zeta potential
(large negative or positive )
Zeta potential =
Stable dispersion
(will tend particles to repel each other)
=
Unstable dispersion
(no force to prevent the particles
coming together)

29. How to Measure Zeta Potential
 It is measured in mV.
 Measurement are made in a Zetasizer Nano Instrument
using laser Doppler electrophoresis.
 The nano series incorporates the patented technique of
M3-PALS(Mixed Mode Measurement Phase Analysis
Light Scattering)
 Electrophoresis is the movement of a charged particle
relative to the liquid it is suspended in under the influence
of applied electric field.

30.  The particles move with a characteristic velocity which is dependent
on:
 Field strength
 Dielectric constant of medium these parameters are known
 Viscosity of the medium
 Zeta potential thus, this can be determined
 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 z f( a)ε κ
3η
where UE = electrophoretic mobility, z= zeta potential, =ε dielectric
constant, = viscosity and f( a) =η κ Henry’s function.

31. FACTORS THAT AFFECTING
ZETA POTENTIAL
pHIonic
Strength

32. PH
 Acid is a positive charge.
 Alkali is a negative charge.
 Imagine a particle in suspension with a negative zeta potential. If
more alkali is added to 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 neutralised.
 Further addition of acid will cause a build up of positive charge.

33.  So, a zeta potential versus pH curve will be positive at low
pH and lower or negative at high pH.
 Isoelectric point is the pH at which a particular molecule or
surface carries no net electrical charge.

34.  Thickness of the double layer ( -1) depends upon theκ
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 valence of the ions will also influence double
layer thickness.
IONIC STRENGTH

35. Inorganic ions can interact with charged surface in one of two
distinct ways
I) 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.
II) non-specific ion adsorption
where they have no effect on the isoelectric point.

36. THANK YOU
FROM:
HAZWA GROUP