NOVEL POLY(VINYL ETHER) BLOCK-COPOLYMERS - ADSORPTION FROM AQUEOUS-SOLUTIONS ON ALPHA-FE2O3 (HEMATITE) AND THE MECHANISM OF COLLOIDAL STABILIZATION

The adsorption of diblock copolymers containing different block length ratios of polyvinylmethyl ether (PVME) and poly (vinyloxy-4-butyric a cid) (PVOBA) from aqueous solutions onto alpha-Fe2O3 (hematite) was co mpared with the adsorption of the PVOBA and PVME homopolymers, The eff ects on the colloidal stabilization in relation to the chemical compos ition of the polymers were evaluated, The pH was between 7.5 and 9 in all experiments, The PVME homopolymer hardly adsorbs on alpha-Fe2O3, w hile an adsorbed amount of 0.31 mg/m(2) was found for PVOBA, which beh aves as a polyelectrolyte at the pH values used, The adsorbed amount o f the black copolymers increases with increasing PVME chain length up to 0.95 mg/m(2). The high affinity character in the adsorption isother m is lost above a certain length of the PVME chain in the block copoly mer. The adsorbed layer thickness increases with the PVME chain length , while at the same time the chain density on the surface decreases. A dsorption of PVOBA causes a high absolute value of the zeta potential (\zeta\) of the alpha-Fe2O3 particles, The value of \zeta\ drops with an increasing length of the PVME chain, The stability of alpha-Fe2O3 d ispersions stabilized with block copolymers with a short PVME chain is mainly due to electrical double-layer repulsion. Full steric stabiliz ation is obtained with sufficiently long PVME chains in the block copo lymer, making these dispersions insensitive to the salt concentration. (C) 1997 Academic Press.