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 acid) (PVOBA) from aqueous solutions onto alpha-Fe2O3 (hematite) was compared with the adsorption of the PVOBA and PVME homopolymers. The effects on the colloidal stabilization in relation to the chemical composition of the polymers were evaluated. The pH was between 7.5 and 9 in all experiments. The PVME homopolymer hardly adsorbs on alpha-Fe2O3, while an adsorbed amount of 0.31 mg/m2 was found for PVOBA, which behaves as a polyelectrolyte at the pH values used. The adsorbed amount of the block copolymers increases with increasing PVME chain length up to 0.95 mg/m2. The high affinity character in the adsorption isotherm is lost above a certain length of the PVME chain in the block copolymer. The adsorbed layer thickness increases with the PVME chain length, while at the same time the chain density on the surface decreases. Adsorption 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 dispersions stabilized with block copolymers with a short PVME chain is mainly due to electrical double-layer repulsion. Full steric stabilization is obtained with sufficiently long PVME chains in the block copolymer, making these dispersions insensitive to the salt concentration.
de Laat AWM
Philips Centre for Manufacturing Technology, SAQ 1314, Eindhoven, 5600 MD, The Netherlands
Schoo
HFM