kolloids

Colloids are mixtures in which one substance consists of microscopically dispersed particles distributed throughout another substance. The dispersed phase typically contains particles about 1 to 1000 nanometers in diameter. Because of their small size, colloidal particles do not form true solutions and do not settle rapidly under gravity; they often exhibit unique optical and rheological properties, and light scattering by the particles can make the Tyndall effect visible.

Colloids are classified by the state of the dispersed phase and the dispersion medium. Common categories include sols (solid in liquid), gels (colloidal solids in a liquid that behave like solids), emulsions (liquid in liquid), foams (gas in liquid or solid), and aerosols (solid or liquid in a gas). Examples include milk (fat droplets in water), paint (pigment particles in a liquid vehicle), fog (liquid droplets in air), and smoke (solid particles in air). In contrast to true solutions, colloids contain particles large enough to scatter light and interact with surfaces without completely dissolving.

Stability in colloids often arises from electrostatic repulsion between similarly charged particles or from steric stabilization by adsorbed polymers or surfactants. External conditions such as changes in pH, ionic strength, temperature, or the presence of electrolytes can cause coagulation or flocculation, leading to separation or gelation. Brownian motion also helps keep dispersed particles from settling quickly.

Colloids play essential roles in food, medicine, cosmetics, materials science, and environmental processes. They enable controlled textures, consistent dispersions, and advanced materials such as gels, emulsions, and nanostructured coatings. The field studies the behavior, stability, and applications of dispersed systems across chemistry, physics, and engineering.