2.KINETIC PROPERTY
a)Brownian Movement-: The colloidal in dispersion are always in a state of random motion.*This random motion can be abserved under ultra microsocpe.
*It was first observed by Robert Brown.
*The velocity of the partiles increase with the decrease in particle size.
b) Diffusion-: Particle diffusion from a region of higher concentrations to lower concentration until the system is uniform.
*The rate of diffusion is experessed by FICKED'S FIRST LAW –
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C) Sedimentation-: the colloidal dispersion, the brownian movement tend to disterb sedimentation.
*There force stronger force must be applied for sedimentation.
*Ultra centrifuge is used for studying sedimentation.
d) Viscosity-: Viscosity is an expression of resistance to flow under applied street (pressure).
*The more viscous a liquid, the grater the applied force to make it flow.
*Viscosity study provide shape of particle in solution.
3. Electrical property
When an electric is applied to a colloidal dispersion, the particle carrieing charge move toword opposite charge electrode.
The negative charged particle (such as kaoline and sulphur) move towards anode.
The positive charged particle ( such as metal hydroxide and ferric hydroxide) move toword cathode.
The rate of particle movement is observed by ultra microscope.
The rate of movement is a function of charge on the particle and related to zeta potential.
Zeta potential can be calculate by
Where ---:
S = Zeta potential in volt
V = Velocity of movement of colloidal particle
E = Applied potential
n = Viscosity of the medium
e = Dielectric constant
EFFECT OF ELECTROLYTES
Consider a solid surface carrying a negative charge and is in contact with Aqous solution containg both positive and negative ion.
The positively charged solid surface will influence distribution of ions.
The thermal mostion also influence distribution of charges.
The resulting effect will be formation of electric double layers.
Ex- AgVo3 +Na I ------------- Ag I + Na Vo3
The surface of AgI contains more I ions than Ag+ ion.
Aqours solution contain large amount of Na+ ion and No3 and tracks of H+ and oH-.
AgI surface is negative charge due to I ions.
It attract positive ions( Na+) towards it surface.
The thermal motion cavses equal distribution of ion.
Na+ concentration is high over I ion surface and from compact as stern layer.
An other layer of Na3- ion forms called as gally chaman layer.
Thus combination of 2 layer opposite charge are called os electrical double layer.
Protective Action
Large concentration of hydrophilic colloids increase the stability of hydrophilic colloids towards precipitation by electrolyte.The hydrophilic colloids adsorb on the surface of hydrophobic colloids and from a protective layer.
This layer prevent them from precipitation on addition of electrolyte.
The phenomenon is constant as protection or protection action.
Most stable ion not reach the colloidal particle no coagulation.
When bismuth sub nitrate is suspended in Tragaenth dispersion.
These phenomena involve coagulation of gum by bismuth ion.
The flocculated gum aggregation with the bismuth ion to from gel or hard cake.
If phosphate citrate or tartrate aded.
The protect from coagulation influence of bismuth ion.
PEPTIZATION
Some ionic material get adserbed on the surface of finally divided solid and convert it into colloidal dispersion.
COACERVATION (phase separation)
The phenomena in which a micro molecule dispersion on mixing separation into two layer is called as coacervation.
Ex. Creative is positively charged below pH 4.7 .
Acacia is negative change at this pH.
When they 2 are mixed together, two layer are formed.
The upper layer of low viscosity have poor concentration of colloidal material.
The lower layer hae thighs viscosity contain high concentration material.
