Download - IMK 209 presentation
FORCES BETWEEN COLLOIDAL PARTICLES
Hye everyone.......
Types of electrostatic forces
repulsive and interactive..
Main forces that affect the colloids system…
Van Der Waals attractive forces
electrostatic repulsive forces
VAN DER WAALS ATTRACTIVE FORCES…
interaction between two dipoles (permanent or induced)
temporary dipole induced a dipole particle nearby.
ELECTROSTATIC REPULSIVE FORCES..
Colloidal particles often carry an electrical charge
attract or repel each other
Higher repulsive force – form electrically change double layer
DLVO THEORY
The DLVO theory, named after the two Russian
scientists (Derjaguin and Laudau) and the two
Dutch scientists (Verwey and Overbeek) who
developed it around the 1940’s, is a corner
stone of colloid science.
Lev Davidovich Landau
Boris Vladimirovich Derjaguin
Verwey
Overbeek
It combines the effects of the London dispersion
van der Waals attraction and the electrostatic
repulsion due to the overlap of the double layer of
counterions.
The central concept of the DLVO theory is that the
total interaction energy of two surfaces or particles
is given by the summation of the attractive and
repulsive contributions.
This can be written as:
VT = VA + VR
VT The total interaction energy VR The repulsive double layer interaction
energy VA The attractive London-van der Waals
energy
Suggests that double-layer repulsion will stabilize emulsion, when the electrolyte concentration phase is less than a certain value.
For small distances, the sum of the two energies is always – ve (i.e. net attractive) ⟹ cause aggregation
When the sum of two energies is + ve ⟹ repulsive force
The Electrical Double Layer
Development of a net charge at the particle surface affects the distribution of ions in the surrounding interfacial region, resulting in an increased concentration of counter ions (ions of opposite charge to that of the particle) close to the surface
Thus an electrical double layer exists round each particle
An electrical double layer exists around each particle.
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 this diffuse layer is a notional boundary known as the slipping plane, within which the particle acts as a single entity
The potential at this boundary is known as the zeta potential
Zeta potential is ~~~ Scientific term of eletrokinetic potential in a colloidal system. Denoted as ζ-potential.The potential difference between the dispersion medium and the stationery layer of fluid attached to the dispersed particle.
What is zeta potential???
Zeta potential related to the stability of colloidal dispersion.
Zeta potential indicates the degree of repulsion between adjacent, similarly charged particle in the dispersion.
When the potential is low, attraction exceeds repulsion and the dispersion will break and coagulate. Considered as not stable.
When the potential is high, repulsion force is higher than attraction force, the dispersion is considerable stable.
Zeta potential [mV]Stability behavior of the colloid
from 0 to ±5, Rapid coagulation or flocculation
from ±10 to ±30Incipient instability
from ±30 to ±40 Moderate stability
from ±40 to ±60 Good stability
more than ±61 Excellent stability
Electrostatically stabilized emulsion sensitiveionic strengthpH
Counterions aroud charged particle surface is
compressed by[salt][H+]
Electrical charge in many food emulsifiers-
sensitivepH (aqueous phase) Protein-
stabilized emulsion
decreases as pH
isoelectric point
EFFECTS OF IONIC
STRENGTH & pH IN
COLLOIDAL PARTICLES