Repulsive forces can be brought into play with the purpose of overcoming the innate attraction between particles and so stabilizing dispersions. Two methods of stabilization are in use: one is electrostatic, based on the repulsion of like charges; the other is steric, based on the repulsion of adsorbed polymers. A mathematical analysis of electrostatic repulsion reveals that it becomes less effective the smaller the particle size and is not significant below a diameter of a few tenths of a micron. Fortunately, the opposite is true of steric repulsion, which at particle diameters greater than a few tenths of a micron would require polymers of too great a length and solubility to be readily found. Both electrostatic and steric stabilities operate in nonpolar media. Combining the two modes into one electrosteric system is possible and allows a wide distribution of particle sizes to be kept in stable dispersion.
Keywords: critical flocculation temperature, Debye-Hückel approximation,
Derjaguin approximation, electrostatic repulsion, electrosteric repulsion,
lyophobic colloid, protective colloid
| text book | other
resources | home