Reversible Thermal Flocculation of Aqueous α-Fe2O3Dispersions Stabilized with Novel Poly(Vinyl Ether) Block Copolymers

The colloidal stability with respect to temperature of aqueous α-Fe₂O₃dispersions stabilized with novel poly(vinylmethylether)-block-poly(vinyloxy-4-butyric acid) diblock copolymers was studied by rheological and turbidimetric measurements. Adsorption of the block copolymers provides the particles with a steric barrier due to the nonadsorbing poly(vinylmethylether) (PVME) blocks. Rheological measurements on concentrated (15 vol %) dispersions showed that flocculation occurred near the θ temperature of PVME in water. For the turbidimetric analysis, the fraction of small particles was used at a very low concentration. With these dispersions, flocculation was found at higher temperatures, corresponding to the lower critical solution temperature of the block copolymer used. The particles spontaneously redispersed when a heated and flocculated dispersion was cooled to below the flocculation temperature.