the early stages of development of the theory of colloidal systems, it was thought that the molecular-kinetic properties inherent only true solutions.Long-term studies it was shown that these properties are inherent and colloidal solutions.It was established that between them there is no qualitative differences, but there are only quantitative, which depend mainly on the size and shape of colloidal particles (micelles).Therefore, the discovery of Brownian motion in this sense was of great importance.
the first time (in 1827), Brownian motion was studied English botanist Robert Brown.Watching a ultramicroscope of flower pollen suspended in a drop of water, scientists discovered that microscopic particles of pollen irregularly (randomly), and constantly moved.Brownian motion - it is disorderly, chaotic or zigzag motion of microparticles.Numerous studies have established that the random motion of molecules is caused by particle size, temperature and viscosity of the dispersion medium.At the same time the nature of the substance has virtually no effect on their movement.
Brownian motion and modern molecular-kinetic theory of liquids
Frankel suggested that the displacement of one molecule rearrangement occurs nearby, each of which tends to occupy its former position, which is most advantageous in terms of energy.
a result of abrupt and continuous movement of the process of self-diffusion of molecules.Dissolved in a liquid microparticles (dispersion phase) perform a movement approximately the same as the molecules of the solvent (dispersion medium).Due to the continuous chaotic motion they are actively moving and do not stay in any place.
Brownian motion of particles colloids and suspensions is due to thermal motion of the particles of the environment and their chaotic strokes of the molecule.As a result of such an attack microparticles randomly move in the space (dispersion medium).These movements are obtained as a result of attacks over time studies (one second of certain molecules can experience up to 1020 strokes).Given the small size of the molecules get different amounts of punches from different angles, they are moving in different directions.With a diameter of more than five micrometres of microparticles Brownian motion is practically not observed.Increasing the size and molecular weight of their absorbs shock.Therefore, the particles of high molecular weight (up to five micrometers) perform only rotational vibration.
Brownian motion and diffusion
As a result of Brownian and thermal motion are equalized concentration of molecules in the entire volume of the solution.Diffusion may occur in colloidal and genuine solutions.
osmotic pressure caused by the presence of micelles.Due to the large size of the molecules and low concentrations of pressure is very low.Of course, part of the analyte in the pressure colloidal solutions depends on the presence of impurities different electrolytes.Thus, macromolecular solutions - polysaccharides, rubber, fibers - at a concentration of 10-12 percent have significant osmotic pressure.Thanks to a special device (osmometers), it was determined the osmotic pressure of blood plasma, which is an average of about 25 mm Hg.It is proved, that the pressure is directly proportional to the concentration of dissolved substances in colloidal or true solutions.
