Experimental and theoretical study of phase transitions induced in colloidal dispersions by associative polymers

We present experimental evidence for reversible phase transitions in aqueous dispersions of acrylic lattices upon addition of two types of hydrophobically modified water-soluble polymers: hydroxyethyl cellulose with randomly placed hydrophobes, and poly(ethylene oxide) with hydrophobic end groups. In the limit of very weak polymer-particle associations flocculation occurs via depletion attraction, while strong associations lead to bridging flocculation with restabilization at higher polymer concentrations. Our observations for the end-modified poly(ethylene oxide) agree well with the predictions of our pseudo-one-component model, which we review briefly. This theory predicts the dependence of the phase transition on the polymer molecular weight and hydrophobic substitution, as well as the nature of the phase transition (fluid-fluid or fluid-solid) and the compositions of the resulting phases.