Dr. Dmitri Kopeliovich
Dispersion (dispersed system) is a mixtures of two substances, one of which (dispersed phase) is distributed in form of subdivided particles throughout another substance (continuous phase, dispersion medium).
Molecular dispersion is a true solutions of a solute phase in a solvent. The dispersed phase (solute) is in form of separate molecules homogeneously distributed throughout the dispersion medium(solvent). The molecule size is less than 1 nm (4*10-8 inch). The examples of molecular dispersions: air (a molecular mixture of Oxygen, Nitrogen and some other gases), elctrolytes (aqueous solutions of salts), metal alloys Solid solutions.
Colloids are micro-heterogeneous dispersed systems, in which the size of the dispersed phase particles is within the range 1 - 1000 nm (4*10-8 - 4*10-5 inch). The colloids phases can not be separated under gravity, centrifugal or other forces. Dispersed phase of colloids may be separated from the dispersion medium by micro-filtration. The examples of colloids: milk (emulsion of fat and some other substances in water), fog (aerosol of water micro-droplets in air), opal (colloidal silica), Silica aerogel monolith, Alumina aerogel monolith.
Coarse dispersions are heterogeneous dispersed systems, in which the dispersed phase particles are larger than 1000 nm (4*10-5“). Coarse dispersions are characterized by relatively fast sedimentation of the dispersed phase caused by gravity or other forces. Dispersed phase of coarse dispersions may be easily separated from the continuous phase by filtration.