Protected lyophobic colloids

The process in which small amounts of added hydrophilic colloidal material make a hydrophobic colloid more sensitive to coagulation by electrolyte. Example the addition of polyelectrolyte to an oil-in-water emulsion to promote demulsification by salting out. Higher additions of the same material usually make the emulsion less sensitive to coagulation, and this is termed protective action or protection . The protected, colloidally stable dispersions that result in the latter case are termed protected lyophobic colloids . 

Lyophobic colloids are inherentiy unstabie with respect to aggregation of the particles and separation Into macroscopic phases, it, therefore, comes as a surprise that a goid sol prepared by Michael Faraday as far back as 1857 still retains its stability (it is kept in the museum of the Royal Society). Subsequent investigations have demonstrated that Faraday s gold sol owes its astonishing longevity to a protective colloid which Faraday must have added. 

Figure 3.6. Illustration of sensitization and protection by a lyophobic colloidal solution.

Rebinder (48) investigated the effect of the surface (adsorption) layers on the properties of colloidal systems. When the lyophobic dispersion systems are stable, the structural-mechanical stabilization occurs where the protecting layers of the micelle-forming surface-active agents or high-molecular compounds are formed at the interface boundary. 

Suspension Lyophobic Polymeric or protective colloid Mainly Batch 10-500 //.m 155,187-191... 

The most conspicuous influence of the addition of lyophilic colloids to lyophobic ones is the protective action" A sufficient (usually not very large) quantity of , for instance, gelatin makes a lyophobic sol much less susceptible to flocculation by electrolytes Electrophoresis measurements show that the electrophoretic velocity of the hydrophobic particles has changed by the addition of the gelatin from the value of the pure hydrophobic sol to a value proper to the pure gelatin soL... 

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