Friday, December 13, 2013

Properties Of Colloids


  • Kinetic property
  • Optical property
  • Electrical property
Kinetic Property: ( Brownian movement )
          In 1827 botanist Robert Brown observe the movement of plant spores floating in water.The molecules of the dispersion medium constantly colloid with the colloidal particles thereby passing kinetic energy to them. The continuous rapid zig-zag motion of the colloidal particle in the dispersion medium is called Brownian movement. This is due to the bombardment of colloidal particles by molecules of the dispersion medium. the particle motion depends on the size of the particle and viscosity of the dispersion medium. This phenomenon was latterly found in the case of colloidal solution, when observed ultra-microscopically. It is otherwise known as Brownian motion or Pedesis.


Optical property: ( Tyndall effect )
           A British physicist John Tyndall in 1869 first observed this phenomenon and hence it is known as Tyndall effect.
           A beam of light is passed through a true solution, the light beam is not visible in this case. But in the case of colloidal solution light beam is visible. This is due to the colloidal particles absorb light energy and then emit it in all directions. It illuminates the path of the beam. This phenomenon of illuminated beam formed by the particles is called Tyndall effect. The amount of scattering depends on the frequency of the light and density of particles. It is otherwise known as Tyndall scattering.
Example:
  • Illumination of light beam from projector in smoke filled theater's.
  • Visible beam of headlights in fog. 

Electrical Properties:
Electrophoresis:
        The movement of the colloidal particles under the influence of an applied electric potential is called as Electrophoresis. If the sol particles are negatively charged, they migrate towards the positive electrodes. this is called Cataphoresis. If the sol particles are positively charged, they migrate towards the negative electrode. This is called Anaphoresis.

Process:
  • Placing the colloidal solution in 'U' tube.
  • Two platinum electrodes are dipped into deionized water.
  • Electric current is passed, the charged colloidal particles move towards the positive electrode side.

Electro-osmosis:
       The dispersion medium itself begins to move under the influence of an electric current. This phenomenon is known as Electro-osmosis. 

Process:
  • Placing the colloidal solution in 'U' tube.
  • Two platinum electrodes are dipped into deionized water.
  • Electric current is applied, the movement of the medium towards the negative electrode.