Colloids dispersed Systems


Sedimentation Potential Streaming Potential



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COLLOIDS Kholmirzayev

Sedimentation Potential

Streaming Potential

  • Differs from electro-osmosis in that the potential is created by forcing a liquid to flow through a bed or plug of particles.

Stability of colloids

Stability of colloids

  • Stabilization serves to prevent colloids from aggregation.
  • The presence and magnitude, or absence of a charge on a colloidal particle is an important factor in the stability of colloids.
  • Two main mechanisms for colloid stabilization:
  • 1-Steric stabilization i.e. surrounding each particle with a protective solvent sheath which prevent adherence due to Brownian movement

    2-electrostatic stabilization i.e. providing the particles with electric charge

Stability of colloids

A- Lyophobic sols:

  • Unstable.
  • The particles stabilized only by the presence of electrical charges on their surfaces through the addition of small amount of electrolytes.
  • The like charges produce repulsion which prevent coagulation of the particles and subsequent settling.
  • Addition of electrolytes beyond necessary for maximum stability results in accumulation of opposite ions and decrease zeta potential coagulation precipitation of colloids.

Stability of colloids

Stability of colloids

  • Coagulation also result from mixing of oppositely charged colloids.
  • B- Lyophilic sols and association colloids:

  • Stable
  • Present as true solution
  • Addition of moderate amounts of electrolytes not cause coagulation (opposite lyophobic)
  • ** Salting out:

    Definition: agglomeration and precipitation of lyophilic colloids.

Stability of colloids

  • This is obtained by:
  • 1- Addition of large amounts of electrolytes

  • Anions arranged in a decreasing order of precipitating power: citrate > tartrate > sulfate > acetate > chloride> nitrate > bromide > iodide
  • The precipitation power is directly related to the hydration of the ion and its ability to separate water molecules from colloidal particles

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