nylmethylether) (PVME) are reported to have a cloud point, The colloidal stability with respect to temperature of aqueous or a lower critical solution temperature (LCST), between a-Fe 2 O 3 dispersions stabilized with novel poly(vinylmethylether)-32 and 35ЊC (4-8). The u temperature, which corresponds block-poly(vinyloxy-4-butyric acid) diblock copolymers was studto the LCST for a chain of infinite length, was estimated to ied by rheological and turbidimetric measurements. Adsorption of be close to 30ЊC (4). This temperature-dependent solubility the block copolymers provides the particles with a steric barrier of PVME in water can be used for the present purpose.
due to the nonadsorbing poly(vinylmethylether) (PVME) blocks.
Incipient flocculation of sterically stabilized particles is ex-
Rheological measurements on concentrated (15 vol %) dispersions
pected to occur close to the u temperature of the polymer showed that flocculation occurred near the u temperature of that makes up the steric barrier (3).
PVME in water. For the turbidimetric analysis, the fraction of small particles was used at a very low concentration. With these
Novel poly ( vinylmethylether ) -block-poly ( vinyloxydispersions, flocculation was found at higher temperatures, corre-4-butyric acid ) ( PVME-b-PVOBA ) diblock copolymers sponding to the lower critical solution temperature of the block were synthesized for the steric stabilization of particles copolymer used. The particles spontaneously redispersed when a ( 9 ) . A set of polymers with different block-length ratios heated and flocculated dispersion was cooled to below the floccuwas made. The objective was to use the PVOBA block lation temperature. ᭧ 1998 Academic Press for adsorption, and the PVME block for making up the Key Words: poly(vinyl ether) block copolymers; a-Fe 2 O 3 ; aquesteric barrier. ous dispersions; reversible thermal flocculation.
The principle of operation was studied with a-Fe 2 O 3 particles. The polymers were tested for their ability to stabilize a-Fe 2 O 3 particles in water (9). Using a block copolymer 1. The Block Copolymers.