Colloid

A colloid is a substance in the form of Liquide or of Gel which contains in suspension of the sufficiently small particles so that the mixture is homogeneous. It does not diffuse through the hémi-permeable membranes, and, in a fluid, it forms a homogeneous dispersion of particles whose dimensions go from 2 to 200 nanometers. The Adhesive S and the Gel S are colloids and form suspensions known as colloidal. The colloidal suspensions are intermediate between the suspension S (particles of size higher than 200 Nm) and the true solution S (particles of size lower than 2 Nm).

One distinguishes:

  • the ground S: solid in liquids;
  • the emulsion S: liquids in liquids;
  • the Aerosol S: solids or liquids in gases;
  • the Freezing S: network of giant molecules or Micelle S.

The Pectin (polysaccharide), some Protein S, the such Egg albumin or the Gelatin, forms solutions colloidal, known as macromolecular and makes it possible to manufacture blanks and frosts. Others Glucid S of high molecular weight, the such Starch or the Cellulose, can also form colloids. The Painting S without odor, the Milk or the blood plasma are colloidal solutions. The metals, like the money ( Collargol ) or the Gold, can be presented in the form of colloidal solution, although it is rather about microphone-suspension. The compounds Tensio-actif S (Detergent S) form colloidal solutions known as micellar. The photographic films are gel.

The stability of a colloidal solution results from balance between the gravitational interactions and the repulsive interactions which are exerted on the particles. These interactions depend in particular on the Température, the '' p '' H and on the electrolyte S dissolved: the Clay S and Limon S form colloidal solutions which flocculate in the presence of metals or of Sel S, which explains the silting of the Estuaire S.

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