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Chapter 19

Forces of Repulsion

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









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