Brownian motion: General information.

In the early stages of development of the doctrine of colloidal systems was considered that the molecular-kinetic properties inherent only in true solutions. Years of studies have shown that these properties are inherent to colloidal solutions. It is established that between them there are qualitative differences, and 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.

For the First time (in 1827) the Brownian motion was studied by the English botanist Robert Brown. Watching under ultramicroscope for flower pollen of plants suspended in a drop of water, scientist have discovered that microscopic particles of pollen indiscriminately (randomly) and move continuously. Brownian motion-the irregular, zigzag or chaotic movement of microparticles. Numerous studies have found that chaotic motion of molecules is determined by the particle size, temperature and viscosity of the dispersion medium. The nature of the substance has virtually no effect on their movement.

Brownian motion and a modern, molecular-kinetic theory of liquids

Frankel suggested that the displacement of a molecule is the rearrangement of the nearby, each of them tends to occupy its original position, which is most beneficial in the energy respect.

As a result of abrupt and continuous movement of molecules occurs in the process of self-diffusion. Dissolved in the liquid micro-particles (dispersion phase) travel about the same as the molecules of the solvent (dispersion medium). Due to the continuous chaotic motion, they actively move and do not remain in any place.

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Brownian motion of the particles of colloids and suspensions occur due to thermal motion of the particles of the environment and their chaotic strikes this molecule. As a result of such attacks microparticles are randomly moving in space (dispersion medium). These movements result from the action of blows for a certain time (one second specific molecule can have up to 1020 BPM). Given the fact that the molecules of small size get different number of strokes from different angles, they move in different directions. When the diameter of the microparticles is more than five micrometers, the Brownian motion is almost not observed. The increase in the size and molecular weight compensates them strikes. Therefore, particles with a high molecular weight (up to five microns) make only oscillatory rotation.

Brownian motion and diffusion

As a result of Brownian and thermal motion is equalized concentration of molecules throughout the volume of the solution. Diffusion can occur in colloidal and true solutions.

The Osmotic pressure is caused by the presence of micelles. Due to the large size of the molecules and low concentrations, their pressure is very low. Of course, part of the analysis of the pressure in colloidal solutions depends largely on the presence of impurities of various electrolytes. So, macromolecular solutions — polysaccharides, rubber, proteins — at 10-12% concentration have significant osmotic pressure. Thanks to special devices (osmometry), it was determined the osmotic pressure of blood plasma, which averages about 25 mm Hg. It is proved that the pressure is directly proportional to the concentration of dissolved substances in a colloidal and true solutions.