EXPLAINS WHAT IS AN ELECTRICAL DOUBLE LAYER AND HOW IT FORMS INCLUDES DISTRIBUTION OF IONS AROUND A PARTICLE OF SUSPENSION HOW THE IONS GET ADSORBED ON THE SURFACE OF SUSPENDED PARTICLE AND HOW IT AFFECTS DISTRIBUTION OF REST OF THE IONS IN THE LIQUID PHASE EXPLAIN DIFFERENT POTENTIALS ACROSS ZETA POTENTIAL NERNST POTENTIAL ETC.

1. ELECTRICAL
PROPERTIES OF
INTERFACE

2. The Electric Double Layer

3. a-a’ : Solid- Liquid Interface with Potential-determining Ions
b-b’ : Shear Plane (Solvated Layer)
a-a’ to b-b’ : Tightly bound layer with counter ions (Stern Layer)
b-b’ to c-c’ : Gouy Layer (Diffuse Second Layer)
c-c’ : Electroneutral region

4. SOLID- LIQUID INTERFACE WITH POTENTIAL-
DETERMINING IONS
Consider the solid particles in a suspension prefer to adsorb POSITIVE ions on
its surface in an aqueous solution containing both positive and negative ions due
to dissociation of salts
The ions which adsorbed on the surface are called POTENTIAL
DETERMINING IONS
These potential determining ions influence the distribution of the ions in the
solution around the suspended particle
The positive potential determining ions will repel the other positive ions in the
solution and attract negative ions towards it

5. TIGHTLY BOUND LAYER WITH COUNTER IONS
(STERN LAYER)
The negative ions will attracted and held close to the solid surface
These negative ions are called COUNTER IONS or GEGENIONS
This layer is immediately adjacent to the surface
Thermal motion also will try for the equal distribution of the ions in the solution
When particles move relative to the liquid, the tightly bound layer also moves
along
Thus particle surface extend upto b-b’rather than a-a’
The boundary b-b’is called shear plane
The number of anions are less than the adsorbed cations; thus this layer possess
positive charge

6. Gouy Layer (Diffuse Second Layer)
Extends from b-b’to c-c’
Concentration of anions will be more near to b-b’but will gradually decrease as
moves to c-c’
Concentration of cations increases as moves to c-c’
The number of cations and anions will be equal at c-c’and this point is called
ELECTRONEUTRAL REGION

7. Stern Layer (a-a’to –b’) and Gouy layer (b-b’to c-c’) together
called ELECTRICAL DOUBLE LAYER
NERNST POTENTIAL (E): potential of the solid surface due to the presence of
potential determining ions
Also called Electro-thermodynamic Potential
It is the potential difference between the surface and electroneutral region

8. ZETA POTENTIAL : potential observed at the shear plane (surface of the
solvating layer)
Also called Electrokinetic Potential
It is the potential difference between the shear and electroneutral point
Can be determined by using an electrophoretic cell or zeta meter
Based on the movement of particles under the influence of electric field

9. The potential energy will be highest at the surface and decrease
sharply along the STERN LAYER and gradually along GOUY LAYER
and becomes zero at ELECTRONEUTRAL POINT