Effects of polyion adsorption on surface properties of TiO 2

Adsorption of polyions, strongly charged poly(N-ethyl-4-vinylpyridinium) cation (P4VP) weakly charged poly(allylammonium) cation (PAH) and weakly charged poly(acrylate) anion (PAA) on TiO 2 surface was investigated. The selected polyions have different functional groups and degree of polyion ionization, which affects the interactions with the TiO 2 surface. The effect of polyion adsorption on the inner surface potential and the electrokinetic potential were measured and analyzed. The inner surface potential of TiO 2 was measured by means of single crystal (SCr) electrodes with two different crystal orientation (001) and (100). The electrokinetic potential of titania particles was obtained from electrophoretic measurements. In suspensions, uncoated TiO 2 particles tend to aggregate and aggregation is reduced after polyion adsorption. The process of aggregation was monitored measuring the size of the particles. Since the surface charge of TiO 2 and the degree of polyion ionization depend on the composition of the solution, namely on pH and ionic strength, the adsorption of polyions on TiO 2 also depends on these parameters. The contribution of the surface charge and degree of polyion ionization of the selected polyelectrolytes to the rate of aggregation of TiO 2 particles was examined. It was found that in the case of weak polyelectrolyte the degree of polyanion ionization plays significant role in stabilization of titania suspensions.