colloidal dispersion otherwise colloid (rus. коллоидная система otherwise дисперсная система) — a system, in which discrete particles, droplets or bubbles of a dispersed phase, whose size at least in one dimension is in the range from 1 to 1,000 nm, are distributed in the other, usually continuous phase (dispersion medium) differing from the dispersed phase in composition or state of aggregation.

Description

Colloidal systems are a kind of dispersed system in which the size of dispersed phase particles is less than 1 micron. In freely dispersed colloidal systems particles of the dispersed phase in gas or liquid freely and independently participate in intense Brownian motion, uniformly filling the entire volume of the dispersion medium; such systems include, for example, sols and aerosols. In the process of Brownian motion and during stirring colloidal particles collide. If this does not result in the enlargement of particles due to their adhesion (coagulation) or fusion (coalescence), the colloidal systems are called aggregately stable. There are also structured (bonded dispersed) systems that are characterised by the presence of an irregular spatial grid formed by particles of the dispersed phase. The mechanical properties of such systems, which primarily include gels, are determined not only by the properties of the dispersion medium, but also by the properties and number of contacts between the particles of the dispersed phase.

Colloidal systems are formed by condensing a substance in a homogeneous medium (supersaturated solution, vapour, supercooled liquid), if the nucleation centres of a new dispersed phase, i.e. tiny droplets or crystals cannot grow to a size exceeding 10–5–10–4 cm. Condensation often accompanies chemical reactions that produce hardly soluble compounds. Another way of obtaining colloidal systems is spontaneous (in case of lyophilic systems) or forced (in case of lyophobic systems) dispersion. The existence of liquid aggregately stable lyophobic colloidal systems is always due to the presence in the dispersion medium of surface-active substances, i.e. stabilizers. These substances produce an adsorption-solvate protective layer on the particle surfaces and prevent the close approach and coagulation of particles under the action of short-range forces of molecular attraction. The close approach of particles may be impeded by the disjoining pressure of the liquid dispersion medium, which is solvated by molecules or ions of the stabilizer in the adsorption layer; by electrostatic repulsion of like-charged ions adsorbed on the particle surfaces; or by enhanced structural viscosity of the surface protective layer, the so-called structural-mechanical barrier. Various types of colloidal systems are presented in the Table.

Dispersed phase

Dispersion medium

Type of colloidal system

Examples

Liquid

Gas

Aerosol of liquid particles

Fog, haze Solid

Solid

Gas

Aerosol of solid particles

Smoke, dust

Gas

Liquid

Foam

Soap bubbles

Liquid

Liquid

Emulsion

Milk, mayonnaise

Solid

Liquid

Sol, suspension

Ink

Gas

Solid

Solid foam

Polyurethane

Liquid

Solid

Gel

Jelly

Solid

Solid

Solid dispersion

Ruby glass, pearl

Authors

  • Goldt Ilya V.
  • Shlyakhtin Oleg A.

Sources

  1. Colloidal dispersion // Chemical encyclopedia (in Russian). V. 2. — Moscow.: Sovetskaja ehnciklopedija, 1990. 80–82pp.
  2. Colloidal dispersion // The Great Soviet Encyclopedia (in Russian). — Moscow.: Sovetskaja ehnciklopedija, 1969– 1978.
  3. Schramm L. Dictionary of Nanotechnology, Colloid and Interface Science. — Wiley, 2008. — 298 p.

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