Depletion flocculation limitations

It is noteworthy that the maximum of the particle number curve was observed in our experiments also at such concentrations of emulsifier at which the polymerizing system is not depleted of emulsifier vJSlat )[cmc) which was the case for the Experiment 2 (Figure b). Therefore, flocculation of particles is not the consequence of emulsifier lack in the system, as was suggested by Brooks ( ), but is due to the limited capability of its adsorption. 

In HEC-thickened formulations, low-shear-rate viscosities increase with decreasing latex particle size. This effect has been a major limitation in formulating small-particle latices. The phenomenon appears to arise from electro viscous, hydration, or flocculation effects, not a depletion layer mechanism. Associative thickeners achieve efficient viscosity in coating formulations via participation in synthesis and formulation surfactant micelles to form pseudo macromolecules and via an ion-dipole interaction between the cations of surface carboxylate groups on the latex and the ether linkages of the associative thickener. Generally, an excess of synthesis surfactant is found in the production of small-particle latices. The achievement of lower viscosities in small-particle ( 100 nm) latex coatings thickened with associative thickener appears to occur by extensive disruption of the polymer hydrophobe s participation in intermicellar networks. 

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