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