Colloïdales

Colloïdales are used in French to refer to colloidal systems, or more generally to substances in which a dispersed phase consists of nanoscale particles distributed within a continuous phase. In English, these systems are called colloids. Particle sizes typically range from about 1 nanometer to several hundred nanometers. Because of their size, colloidal particles scatter light (the Tyndall effect) and undergo Brownian motion, which helps prevent sedimentation and contributes to stability.

In a colloidal system, the dispersed phase is the finely divided material, and the continuous phase is the surrounding medium. Colloids are commonly classified as hydrophilic or hydrophobic, depending on their affinity for the continuous phase. Stabilization mechanisms include electrostatic repulsion, where charged species adsorb on particle surfaces, and steric stabilization, where polymers or surfactants create a physical barrier to aggregation. Colloidal stability can be threatened by changes in pH, ionic strength, or temperature, leading to aggregation or coagulation (flocculation) and sometimes phase separation.

Common categories include sols (solid particles in liquid), gels (networked solid within liquid), emulsions (one liquid dispersed in another immiscible liquid), foams (gas dispersed in liquids or solids), and aerosols (solid or liquid particles dispersed in a gas). Examples include milk (proteins and fats in water), ink, paint suspensions, fog, and clouds.

Formation methods include dispersion of larger particles and condensation of molecules to form discrete particles. Applications span food, medicine, materials science, cosmetics, and environmental science. Colloidal properties are studied in physical chemistry, including stability theories such as electrostatic double layer and steric stabilization.