Adsorption of partially quarternised poly(vinyl imidazoles) onto SiO 2 and Y 2O 3

Abstract

Partially quarternised poly(vinyl imidazoles) (PVIs) were synthesised and their adsorption at pH 10, where only the quarternary groups are charged, was studied. The adsorbed amount is much higher on SiO 2 surfaces than on Y 2O 3 surfaces. Nevertheless, in 10 −2 M KNO 3 solutions the maximum adsorbed amount of PVI on both surfaces, measured as a function of the degree of quarternisation, exhibits a maximum between 4% and 7% positively charged groups. The hydrodynamic layer thickness of adsorbed PVI has a maximum at the same degree of quarternisation. Moreover, the maximum coincides with the isoelectric point of the SiO 2 or Y 2O 3 particles bearing adsorbed PVI. At degrees of quarternisation higher than 7%, the zeta-potentials of PVI-covered SiO 2 and Y 2O 3 particles are identical. The colloidal stabilisation mechanism of these particles is steric at low (< 10%) degrees of PVI quarternisation, and changes to an electrosteric mechanism at higher degrees of quarternisation. Increasing the salt concentration leads to a small shift in the adsorption maximum to higher degrees of quarternisation. At quarternisation degrees of less than 4%, the adsorption decreases markedly with increasing salt concentration, while at higher degrees of quarternisation the adsorption increases only slightly with salt concentration.