Colloid properties particle movement

A colloid is a suspension of particles with diameters between 1 nm and 100 nm. The particles are charged and can be subjected to cataphoresis (electrophoresis). They are subject to Brownian movement and have a large amount of surface activity. Their properties lie between those of true solutions and coarse suspensions. 

Figure 8-39 Flat Plane Projection of the Location of a Colloidal Particle Subject to Brownian Movement. Source From H. Schubert, Food Particle Technology. Part 1 Properties of Particles and Particulate Food Systems, J. Food Eng., Vol. 6, pp. 1-32,1987, Elsevier Applied Science Publishers, Ltd.

Colloidal dispersions may appear either translucent or cloudy, depending on the type of colloid and the degree of particle concentration and dispersion. The colloidal particles cannot be easily distinguished from water. They possess properties that are very different from other solid settable suspensions and from solutions. When the colloidal particles are < 5 pm, they have erratic aleatory movements known as Brownian movements, caused by collisions with molecules from the dispersion medium. When a light beam passes through a colloidal dispersion, this reflects and scatters light (Tyndall effect). 

The nature and properties of common clay minerals found in petroleum reservoirs are briefly discussed to set the stage for a review of the colloidal and hydrodynamic forces acting on the fine particles. This is followed by a review of reported experimental studies of permeability damage by fines movement under purely hydrodynamic forces. 

In a colloidal dispersion, if the particle is a macromolecule of polyelectrolyte nature, additional properties to the general physicochemical properties may arise. The British physicist Donnan, in 1911, showed that when two solutions of electrolytes arc separated by a semlpermeable membrane, potentials arise at the junction. This happens v icn movement of atleast one of the ions through the semlpermeable membrane is hindered. Th<- hindrance may be due to the colloidal nature of the ion or the electroMe may be chcndcimmobile matrix of macromolecular nature like an ion-exchange resin on oiie side. In addition, an osmotic pressure difference between the two compartments is observed at equilibrium. Tlie explanation for these apparent anomalies was provided by Donnan and therefore the phenomenon, Donnan membrane equilibrium bears his name to this day. 

Electrophoresis This system refers to the movement of the colloidal particle under an applied electric field. In biology, different proteins exhibit different charges and thus can be separated nsing this property. 

One of the characteristic properties of colloidal solutions is the more or less energetic movement of the particles. The closer study of this movement has been made possible by the ultramicroscope. The movement of very small particles can be seen with the ordinary microscope, and has been known since 1827. It was discovered by a botanist, Robert Brown, and has been named after him. It has since been thoroughly investigated by a large number of scientists. A short bibliography relative to the earlier experiments will be found in Lehmann s Molekularphysik, 1, 264 (1867). 

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