koloids

Koloids, or colloids, are systems in which microscopic particles are dispersed throughout another substance, forming a dispersed phase and a continuous phase. The dispersed particles typically range from about 1 nanometer to 1 micrometer in size. Because the particles are small but not dissolved, colloids are distinct from true solutions and suspensions: they often remain dispersed for extended periods and can scatter light, a phenomenon known as the Tyndall effect. Brownian motion also helps keep colloids from settling rapidly.

Colloids are classified by the nature of the dispersed phase and the continuous medium. Common types include sols (solid particles dispersed in a liquid, such as paint or colloidal gold in water), gels (a liquid dispersed in a solid network, as in gelatin), emulsions (one liquid dispersed in another immiscible liquid, such as milk or mayonnaise), foams (gas dispersed in a liquid or solid, such as whipped cream), and aerosols (solid or liquid particles dispersed in a gas, such as fog or smoke). Colloidal systems can involve liquids, solids, or gases as the dispersed or continuous phases.

Stability in colloids is influenced by interparticle forces and external conditions. They can be stabilized by electrostatic repulsion, adsorption of polymers (steric stabilization), or other surface treatments. If stabilization fails, particles may aggregate through coagulation or flocculation, leading to phase separation or gelation.

Preparation methods include dispersion (breaking larger aggregates into smaller particles) and condensation (forming colloidal particles from dissolved species). Colloids have wide applications in food, medicine, cosmetics, paints and coatings, catalysis, and materials science, as well as in environmental and analytical contexts. The term derives from the Greek kolloid, meaning glue, reflecting early observations of sticky, dispersed systems.