Abstract
The incipient flocculation properties of aqueous polymer dispersions, which are stabilized solely by poly(ethylene oxide) moieties, have been investigated. Flocculation was induced by decreasing the solvency of the dispersion medium for the stabilizing chains. The influence of such factors as the anchor polymer, the disperse phase, the particle size, the surface coverage, and the molecular weight of the stabilizing moieties was examined. Flocculation occurs in dispersion media which are either Θ-solvents for the stabilizing moieties or of better solvency than Θ-solvents. Both aqueous and nonaqueous dispersions, which are stabilized solely by amphipathic nonionic macromolecules, exhibit remarkably parallel flocculation phenomenology. The stability of both types of dispersions is therefore amenable to a common theoretical approach. However, the phase diagrams for aqueous and nonaqueous polymer solutions may be very different. Measurements of the thermodynamic parameters which govern stability demonstrate that, whereas entropic effects may govern stability in nonaqueous systems, enthalpic interactions provide the stabilization mechanism in the aqueous dispersion studied. A general scheme which distinguishes seventeen different thermodynamic situations in the stability-flocculation domain is presented. Stability is shown to originate in entropic effects, enthalpic interactions, or a combination of both.
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