Disperse systems: general characteristics and classification

Colloid chemistry is a science that studies the methods of preparation, composition, internal structure, chemical and physical properties of disperse systems. Disperse systems are systems that consist of fragmented particles (dispersed phase) distributed in the surrounding (disperse) medium: gases, liquids or solids. The particle size of the dispersion phase (crystals, droplets, bubbles) differs in the degree of dispersion, the magnitude of which is directly proportional to the size of the particles. In addition, dispersed particles are distinguished by other characteristics, as a rule, according to the aggregate state of the dispersed phase and the medium.

Disperse systems and their classification

The entire dispersion system can be classified according to the size of the particles of the dispersion phase into molecular-ion (less than one nm), colloidal (from one to one hundred nm), coarsely dispersed (more than one hundred nm).

Molecular dispersed systems. These systems contain particles whose size does not exceed one nm. This group includes a variety of true solutions of nonelectrolytes: glucose, urea, alcohol, sucrose.

Coarse-dispersed systems are characterized by the largest particles. These include emulsions and suspensions. Dispersed systems in which the solid is localized in a liquid dispersion medium (starch solution, clay) are called suspensions. Emulsions are systems that are obtained by mixing two liquids, one in the form of droplets dispersed in another (oil, toluene, benzene in water or droplets of triacylglycerols (fat) in milk.

Colloidal disperse systems . In them, the sizes of colloidal particles reach up to 100 nm. Such particles easily penetrate the pores of paper filters, but do not penetrate the pores of biological membranes of plants and animals. Since colloidal particles (micelles) have electrical charge and solvate ionic shells, due to which they remain suspended, they can not precipitate for a long time. A vivid example of a colloidal system are solutions of gelatin, albumin, gum arabic, colloidal solutions of gold and silver.

The degree of dispersity makes it possible to distinguish between homogeneous and heterogeneous disperse systems. In homogeneous disperse systems, the phase particles are ground to molecules, atoms and ions. An example of such dispersion systems can be a solution of glucose in water (molecular dispersion system) and a kitchen salt in water (ion-dispersed system). They are true solutions. The size of the molecules of the dispersed phase does not exceed one nanometer.

Disperse systems and solutions

Of all the systems and solutions represented in life of living organisms, the most important are colloidal disperse systems. As is known, the chemical basis for the existence of a living organism is the exchange of proteins in it. On average, the protein concentration in the body is from 18 to 21%. Most proteins dissolve in water (the concentration of which in the human body and animals is approximately 65%) and form colloidal solutions.

There are two groups of colloidal solutions: liquid (sols) and gel-like (gels). All life processes that occur in living organisms are associated with the colloidal state of matter. In each living cell, biopolymers (nucleic acids, proteins, glycosaminoglycans, glycogen) are in the form of disperse systems.

Colloidal solutions are also widespread in inanimate nature. Such solutions include oil, fabrics, plastics, synthetic fibers. A variety of food products can be attributed to colloidal solutions: kefir, milk, etc. Most drugs (serums, antigens, vaccines) are colloidal solutions. To the colloidal solutions include paint.