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Dr. Dmitri Kopeliovich
Depending on the affinity of the dispersion media for the dispersed phase two types of Colloids exist:
Lyophilic (liquid loving) Colloids are characterized by strong affinity of the dispersion media molecules for the surface molecules of the dispersed phase.
Dispersed phase of lyophilic colloids is wetted by the continuous phase.
Each particle of lyophilic colloids is solvated - coated with a monomolecular layer of the dispersion media.
Dispersed particles of intrinsic shape and some polymer molecules may entrap additional molecules of the dispersion media resulting in higher solvation of the colloid system.
Due to solvation lyophilic colloids are more viscous than the dispersion media.
If the dispersed polymer molecules are cross-linked they form a network structure, in which all the dispersion media is mechanically entrapped. Properties of such colloids (gels) are similar to those of solid.
Formation of lyophilic colloids is spontaneous (mechanical agitation is not required). The colloids are thermodynamically stable. The average size of the dispersed particles is determined by the value of the interfacial tension and the temperature.
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Lyophobic (liquid hating) Colloids consist of the phases, which do not interact between each other.
Dispersed phase in lyophobic colloids is not solvated by the dispersion media.
Lyophobic colloids are prepared by mechanical agitation, which is required because of high interfacial energy of the dispersed particles.
Lyophobic colloids are thermodynamically unstable. Their dispersed particles have a tendency to aggregation or coalescence.
Thermodynamic stability of lypophobic colloids may be increased by an addition of relatively small amount of surface active substances (surfacants) lowering the interfacial energy of the system.
Aerosols and most of water based colloids with inorganic dispersed phase are lyophobic.
Some of lyophobic colloids possess lyophilic properties (eg. hydrosols of silica and alumina).
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