colloïdals

Colloids are mixtures in which a dispersed phase consists of very small particles that are distributed within a continuous phase. The particles are larger than typical molecules but small enough to remain suspended rather than forming a true solution, usually ranging from about 1 nanometer to 1000 nanometers in size. The dispersed and continuous phases can be solids, liquids, or gases, leading to a variety of colloidal systems.

Common colloidal systems include sols (solid in liquid, for example gelatin in water), gels (a solid-like network that holds liquid), emulsions (one liquid dispersed in another immiscible liquid, such as milk), aerosols (tiny particles in a gas, such as fog), and foams (gas dispersed in a liquid or solid). Emulsions and suspensions are related concepts but differ in stability and particle size.

Key properties of colloids include light scattering known as the Tyndall effect, and Brownian motion which helps keep particles from settling quickly. The stability of a colloid depends on the interactions between particles; electrostatic or steric stabilization can prevent aggregation, while changes in ionic strength or pH can lead to coagulation or flocculation. Techniques such as filtration and ultrafiltration can separate colloidal particles based on size.

Colloids appear in many contexts, including foods (dressings, milk), medicines (drug suspensions), materials science (colloidal crystals, pigments), and environmental science (aerosols, colloidal contaminants). The term was introduced in the 19th century by Thomas Graham, from the Greek kolla meaning glue, to describe substances with a glue-like, intermediary state between solutions and suspensions.