• All the molecules or particles carry
out a electric charge due the their
• Electrochemistry and the surface
and colloidal chemistry can be
combine with this phenomena.
5. • An electrical
• Divided into two
• Defined as the
substance by means
of the electric
• Redox reaction was
pushes to the
• Substance that
when dissolved in a
• Solution is
considered as the
• Describes as the
EMF or cell
• The potential
between two cells
• Study of reactions in which
charged particles cross the
interface between two
phases of matter , such as
interface between a solid
and a liquid.
8. Electrical Double Layer Theory
• When electrode immersed in an electrolytic solution, charge
accumulation will occur.
• Particle size should be greater than 1 nm.
• Charge separation always occur at the interface of the electrodes in
• The excess charge on the electrode surface is accumulated by an
accumulation of the excess ions of the opposite charge in the solution.
9. • EDL is a transition region
between two phases consists
1. An inner monomolecular
2. An outer diffuse region
3. A layer intermediate
between inner molecular
layer and the outer diffuse
10. Structure of double layer
• Has 03 structures.
Gouy – Chapman model
Gouy- chapman stern model
11. Helmholtz model
• Described by the Helmholtz in 1879.
• Described that the charge separation at the
interface between metallic electrolyte and an
• The charge of the surface of the metal was
neutralized by the opposite sign of the electrolyte.
12. • The potential in the Helmholtz layer is described by the Poisson’s
φ - Electric potential
ρ - Charge density
x - Distance from the electrode
ε0 - Permittivity of vacuum
εr - Relative permittivity of the medium.
13. • Considering the ions are point charges.
• Electrical double layer act as a capacitor.
14. Drawback of the model
• The model does not account for the dependence of
the measured capacity on potential or electrolyte
• This is the neglect of interactions that occur away
from the OHP.
15. Gouy-Chapman Model
• The thermal motion of the ions near the surface was
• That described that diffuse double layer has an ions which
have the opposite charges with the surface.
• The change in concentration of the counter ions near a
charged surface follows the Boltzmann distribution.
no = bulk concentration
z = charge on the ion
e = charge on a proton
k = Boltzmann constant
16. Gouy- Chapman Stern model
• In 1924 Stern developed this method.
• Combined the two previous models by
adapting the compact layer of ions
used by Helmholtz and next to the
diffuse layer of Gouy Chapman
extending into the bulk solution.
• ions have finite size
• consequently the closest approach of
OHP to the electrode will vary with the
18. Layers of EDL
• Mostly used the Gouy chapman – stern model.
• Two layers can be described.
19. Stern layer
• Also known as the Stationary Layer
• Occurs in next to the surface of the particle.
• Ions are bound to the surface very firmly.
• Occurs due to the absorbing and coulomb interaction.
20. Diffuse Layer
•Occurs next to the stern layer.
•Occurs in between the stern layer and the bulk.
•Both positive and negative charges can be seen.
Boundary Slipping plane
25. Zeta potential
• Term that used in colloidal dispersion for electro kinetic potential.
• Usually denoted using the Greek letter zeta (ζ).
Zeta potential is the potential in the inefficient
double layer at the location of the slipping
plane relative to the point in the bulk away
from the interface.
26. • Depend on the location of the plane.
• Caused by the net electrical charged contained within
the region of bonded by the slipping plane.
• Widely used for quantification of the magnitude of the
• Key indicator of the stability of colloidal dispersions.
• Stern potential ≠ zeta potential
• The value of zeta potential is cannot be measured
directly from experimentally.
27. High ζ
•will confer stability.
•Attractive forces may
exceed this repulsion
•Tend to coagulate or
29. DLVO Theory
• Was named by the scientists named as Derjaguin , Landau, Verwey,
• Very important for suspension of solid.
30. Assumptions of DLVO theory
• Dispersion in dilute.
• Only two forces act on the dispersed particles. Those are
Vanderwaals forces and electrostatic forces.
• The electric charge and other properties are uniformly distributed
over the solid surface.
• The distribution of ions determined by the electrostatic forces,
Brownian motion and the entropic dispersion.
32. VT = VR + VA
VA = Sum of the Vander Waals attractive
VR = Electrical double layer repulsive (VR) forces
VT = Total energy of the double layer
thickness of the double
size of the particle
Electrolyte – ex: water
After dissolving separate into cations and anions
When applying an electric potential to the solution, ions are stared to travel opposite directions. Then electrical current will occurs.
s a structure that appears on the surface of an object when it is exposed to a fluid.
In here object may be a solid particle, a gas bubble, a liquid droplet, or a porous body. The double layer refers to two parallel layers of charge surrounding the object.
The electrode holds a charge density (σM) arising from either an excess (-σM) or deficiency (+σM) of electrons at the electrode surface. The charge on the electrode is balanced by redistribution of the ions in the solution by an equal but oppositely charged amount of ions. The result is two layers of opposite charge separated by some distance and it is limited to the radius d/2 of the attracted ions and a single layer of solvation around each ion.
The line drawn through the center of such ions marks the boundary known as the ‘Outer Helmholtz Plane’ (OHP) and the region within it the electrical double layer. The potential in the Helmholtz layer is described by the Poisson’s equation, which relates the potential with the charge distribution.
Gouy suggested that interfacial potential at the charged surface could be attributed to the presence of a number of ions of given sign attached to its surface, and to an equal number of ions of opposite charge in the solution. In other words, counter ions are not rigidly held, but tend to diffuse into the liquid phase until the counter potential set up by their departure restricts this tendency. The kinetic energy of the counter ions will, in part, affect the thickness of the resulting diffuse double layer. Gouy and, independently, Chapman developed theories of this so called diffuse double layer in which the change in concentration of the counter ions near a charged surface follows the Boltzmann distribution.
Charge opposite to the surface charge
Diffused double layer (DDL) is the result of claywaterelectrolyte interaction. Cations are heldstrongly on the negatively charged surface of dry finegrained soil or clays. These cations are termedas adsorbed cations. Those cations in excess of those needed to neutralize electronegativity of clayparticles and associated anions are present as salt precipitates. When dry clays come in contact withwater, the precipitates can go into solution. The adsorbed cations would try to diffuse away from theclay surface and tries to equalize the concentration throughout pore water. However, this movementof adsorbed cations are restricted or rather minimized by the negative surface charge of clays. Thediffusion tendency of adsorbed cations and electrostatic attraction together would result in cationdistribution adjacent to each clay particle in suspension.
Also it can be defined as the potential difference between the dispersion medium and the stationary layer of fluid attached to the dispersion particle.
At a high zeta potential will confer stability. At the solution or dispersion will resist aggregation. When the potential is small, attractive forces may exceed this repulsion and the dispersion may break and flocculate. So, colloids with high zeta potential (negative or positive) are electrically stabilized while colloids with low zeta potentials tend to coagulate or flocculate.
The stability of a colloidal system will determined by the sumation of the attractive forces and the repulsive forces.
Unlike a ceramic capacitor or aluminum electrolytic capacitor, the Electrical Double Layer Capacitor (EDLC) contains no conventional dielectric.
Triglyceride emulsions are medical products; they are sub micron emulsions of vegetable oils in water, emulsified by phospholipids, which provide a high zeta potential, and a correspondingly long shelf life (2-3 years). The emulsions are used to feed patients intravenously who cannot be fed orally (e.g. due to gastrointestinal surgery).
zeta potential – pH curve for a drug-containing emulsion that is flocculated at pH 7. Data of this type allows a rational selection of formulation pH and emulsifier to maximise zeta potential and hence emulsion stability.zeta potential – pH curve for a drug-containing emulsion that is flocculated at pH 7. Data of this type allows a rational selection of formulation p
H and emulsifier to maximise zeta potential and hence emulsion stability.zeta potential – pH curve for a drug-containing emulsion that is flocculated at pH 7.