Colloid chemistry is a science that studies the methods of preparation, composition, internal structure, chemical and physical properties of dispersed systems. Dispersed systems are systems that consist of fragmented particles (dispersed phase) distributed in the surrounding (dispersed) environment: gases, liquids or solids. The particle sizes of the dispersion phase (crystals, droplets, bubbles) differ in the degree of dispersion, the value of which is directly proportional to the size of the particles. In addition, dispersed particles are distinguished by other signs, as a rule, by the aggregate state of the dispersed phase and medium.
Dispersed systems and their classification
All dispersion systems according to the particle size of the dispersion phase can be classified into molecular-ionic (less than one nm), colloidal (from one to one hundred nm), coarsely dispersed (more than one hundred nm).
Molecularly dispersed systems. These systems contain particles whose size does not exceed one nm. This group includes a variety of true solutions of non-electrolytes: glucose, urea, alcohol, sucrose.
Coarse systems are characterized by the largest particles. These include emulsions and suspensions. Dispersed systems in which a solid is localized in a liquid dispersion medium (a solution of starch, clay) are called suspensions. Emulsions are systems that are obtained by mixing two liquids, where one in the form of droplets is dispersed in the other (oil, toluene, benzene in water or droplets of triacylglycerols (fat) in milk.
Colloidal dispersed systems . In them, the sizes of colloidal particles reach up to 100 nm. Such particles easily penetrate through the pores of paper filters, but do not penetrate through the pores of biological membranes of plants and animals. Since colloidal particles (micelles) have an electric charge and solvate ion shells, due to which they remain in suspension, they may not precipitate for a sufficiently long time. A striking example of the colloidal system are solutions of gelatin, albumin, gum arabic, colloidal solutions of gold and silver.
The degree of dispersion makes it possible to distinguish between homogeneous and heterogeneous disperse systems. In homogeneous dispersed systems, 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 table salt in water (ion-dispersed system). They are true solutions. The size of the molecules of the dispersed phase does not exceed one nanometer.
Dispersed systems and solutions
Of all the systems and solutions presented in the life of living organisms, colloidal dispersed systems are of the greatest importance. As you know, the chemical basis for the existence of a living organism is the exchange of proteins in it. On average, the concentration of proteins in the body is from 18 to 21%. Most proteins dissolve in water (the concentration of which in humans and animals is approximately 65%) and form colloidal solutions.
Two groups of colloidal solutions are distinguished: liquid (sols) and gel-like (gels). All vital processes that occur in living organisms are associated with the colloidal state of matter. In every living cell, biopolymers (nucleic acids, proteins, glycosaminoglycans, glycogen) are in the form of dispersed systems.
Colloidal solutions are also widespread in inanimate nature. Such solutions include oil, fabrics, plastics, synthetic fibers. A lot of food products can be attributed to colloidal solutions: kefir, milk, etc. Most drugs (serums, antigens, vaccines) are colloidal solutions. Colloidal solutions include paints.