Suspension
In
chemistry,
a suspension is a heterogenous mixture containing solid particles that
are sufficiently large for sedimentation. Usually they must be larger than
1 micrometer. The internal phase (solid) is dispersed throughout the external
phase (fluid) through mechanical agitation, with the use of certain excipients
or suspending agents. Unlike colloids, suspensions will eventually settle. An example of a
suspension would be sand in water. The suspended particles are visible under a
microscope and will settle over time if left undisturbed. This distinguishes a
suspension from a colloid,
in which the suspended particles are smaller and do not settle. Colloids and
suspensions are different from solutions, in which the dissolved substance (solute) does not
exist as a solid, and solvent and solute are homogeneously mixed.
A
suspension of liquid droplets or fine solid particles in a gas is called an aerosol
or particulate.
In the atmosphere these consist of fine dust and soot particles, sea salt,
biogenic and volcanogenic sulfates, nitrates, and cloud droplets.
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