Association Colloid

Association Colloid

 

a binary or multicomponent system whose structure and properties are between those of liquid solutions and sols. Association colloids are microheterogeneous systems in which the particles of the colloidal dispersed phase (micelles) are formed by the agglomeration of molecules or ions of the substance dissolved in the dispersion medium. The micelles, or associates, are in thermodynamic equilibrium with the surrounding solution; therefore, a change in the external conditions, the composition of the dissolving medium, or the concentration of the dissolved (dispersed) substance causes redistribution of the substance between the micelles and the solution. Strong dilution or a rise in temperature may cause complete decomposition of all the micelles into their constituent molecules (ions), in which case the system becomes homogeneous, or single-phase. Restoration of the previous conditions returns the system to its original microheterogeneous state. Thus, the characteristic feature of association colloidal systems is the reversibility of the true solution ⇄ sol transformation.

Association colloidal systems include solutions of micelle-forming surface-active substances, such as soap and synthetic detergents, and also certain organic dyes, tanning agents (tannins), and alkaloids.

REFERENCES

Voiutskii, S. S. Kurs kolloidnoi khimii. Moscow, 1964. Page 425.
Peskov, N. P. Fiziko-khimicheskie osnovy kolloidnoi nauki, 2nd ed. Moscow-Leningrad, 1934. Page 431.

L. A. SHITS

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The main fraction of milk proteins, the caseins, occurs in milk as sterically-stabilized association colloids, called casein micelles.

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