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A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid , [ 1 ] while others extend the definition to include substances like aerosols and gels .
A colloidal crystal is an ordered array of colloidal particles and fine grained materials analogous to a standard crystal whose repeating subunits are atoms or molecules. [1] A natural example of this phenomenon can be found in the gem opal, where spheres of silica assume a close-packed locally periodic structure under moderate compression.
Quicksand (also known as sinking sand) is a colloid consisting of fine granular material (such as sand, silt or clay) and water. It forms in saturated loose sand when the sand is suddenly agitated. When water in the sand cannot escape, it creates a liquefied soil that loses strength and cannot support weight.
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Schematic representation of the different stages and routes of the sol–gel technology. In this chemical procedure, a "sol" (a colloidal solution) is formed that then gradually evolves towards the formation of a gel-like diphasic system containing both a liquid phase and solid phase whose morphologies range from discrete particles to continuous polymer networks.
Sols are stable, so that they do not settle down when left undisturbed, and exhibit the Tyndall effect, which is the scattering of light by the particles in the colloid. The size of the particles can vary from 1 nm - 100 nm. Examples include amongst others blood, pigmented ink, cell fluids, paint, antacids and mud.
Colloids are formed by phase separation, though not all phase separations forms colloids - for example oil and water can form separated layers under gravity rather than remaining as microscopic droplets in suspension. A common form of spontaneous phase separation is termed spinodal decomposition; it is described by the Cahn–Hilliard equation.
Air is an example of a solution as well: a homogeneous mixture of gaseous nitrogen solvent, in which oxygen and smaller amounts of other gaseous solutes are dissolved. Mixtures are not limited in either their number of substances or the amounts of those substances, though in most solutions, the solute-to-solvent proportion can only reach a ...