A colloidal suspension consists of a mixture of compounds in which a solid or liquid is suspended in a fluid because of its particle size.
It is possible, for example, for small particles to be held in solution because their size is such that even without added motion (i.e., still air, or an un-mixed liquid), they are too small to settle out in a short period of time. Homogenized milk is a colloidal suspension of fat and other compounds in water, for example. In air, tiny particles of water that are suspended because of their size forms fog or clouds.
Colloid particles typically have sizes between 2 and 1000 nanometers.
In general, a colloid or colloidal dispersion is a substance with components of one or two phases, a type of mixture intermediate between a homogeneous mixture (also called a solution) and a heterogeneous mixture with properties also intermediate between the two.
Colloids may be colored or translucent because of the Tyndall effect, which is the scattering of light by particles in the colloid.
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.
In chemistry, a suspension is a colloidal dispersion (mixture) in which a finely-divided species is combined with another species, with the former being so finely divided and mixed that it doesn't rapidly settle out.
A suspension of liquid droplets or fine solid particles in a gas is called an aerosol.
It is important to distinguish suspensions from solutions which do not separate over any period of time because the intermolecular forces between the different types of molecules are of similar strength to the attraction between molecules of the same type.
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