Colloid

In general, a colloid or colloidal dispersion is a two-phase system of matter; a type of mixture intermediate between homogeneous mixtures and heterogeneous mixtures.

Stabilization of colloid suspensions

Stabilization is the means to keep the colloids from all settling on the ground of the container or glueing together.

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Steric stabilization and electrostatic stabilization are the two main mechanisms for colloid stabilization. Electrostatic stabilization is based on the mutual repulsion of like electrical charges. Different phases generally have different charge affinities, so that a charge double-layer forms at any interface. Small particle sizes lead to enormous surface areas, and this effect is greatly amplified in colloids. In a stable colloid, mass of a dispersed phase is so low that its buoyancy or kinetic energy is too little to overcome the electrostatic repulsion between charged layers of the dispersing phase. The charge on the dispersed particles can be observed by applying an electric field: all particles migrate to the same electrode and therefore must all have the same charge.

Related Topics:
Steric stabilization - Buoyancy - Kinetic energy

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The destruction of a colloid, called coagulation, can be accomplished by heating or by adding an electrolyte. Heating increases the velocities of the particles, causing them to collide with enough energy that the barriers are penetrated and the particles can aggregate. Since this is repeated many times, the particle grows to be large enough to form a precipitate. Adding an electrolyte neutralizes the adsorbed ion layers on the surface of the colloidal particles.

Related Topics:
Coagulation - Electrolyte

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