In the presented paper, the influence of the molecular weight and the type of polyamino acid functional groups on the electrokinetic properties and the stability of chromium (III) oxide suspension were examined. Analysis of the data obtained from the adsorption, potentiometric titration, zeta potential, and stability measurements allows to propose stabilization or destabilization mechanism of the studied systems. In the studies, there were used polyamino acids with different ionic characters: anionic polyaspartic acid and cationic polylysine. The measurements showed that the zeta potential depends on the concentration and molecular weight of the applied polymer. Stability of the chromium (III) oxide suspensions in the presence of ionic polyamino acids increases compared to the results obtained in the absence of polymers. The exception is LYS 4,900 at pH = 10. Under these conditions, the decrease in stability is observed due to formation of polymer bridges between the polymer chains adsorbed on different colloidal particles. Determination of the stabilization/destabilization mechanism of the polyamino acid/chromium (III) oxide system and examination of the effects of polymer molecular weight on the stabilization properties can contribute to a wider use of this group of compounds as potential stabilizers or flocculants in many industrial suspensions.

A new adsorbent consisting of fumed, mixed alumina, silica, and titania in various proportions (AST 50) was investigated. The studied material was prepared by chemical vapor deposition method. The diameter of AST 50 primary particles was equal to about 51 nm which denotes that it can be classified as a nanomaterial. In the presented paper, the adsorption properties of polyvinyl alcohol on the ternary oxide were investigated. The polymer macromolecules were characterized by two different molecular weights and degree of hydrolysis. The polymer adsorption reaches the maximum at pH 3 and decreases with the solution pH rise. The reduction of the adsorbed PVA macromolecules is related to the electrostatic repulsion forces occurring in the studied system. The AST 50 point of zero charge (pH_pzc) obtained from the potentiometric titration is equal to 4.7. Due to the nonionic character of the analyzed macromolecular compound, the polymer attendance has an insignificant effect on the AST 50 surface charge density. In the case of the adsorbent particles zeta potential, the obtained dependencies are different in the absence and presence of PVA. The shift of the slipping plane and displacement of the counter-ions from Stern layer by the adsorbed polymer chains have the greatest effect on the ζ potential value. The stability measurements indicate that the AST 50 suspensions in the presence of the background electrolyte at pH 3 and 6 are unstable. In turn, in an alkaline medium the mixed oxide suspensions exhibit the highest durability, which is a result of a large number of the negative charges on the AST 50 surface. The addition of PVA 100 significantly improves the suspension stability at pH 3 and 6; at higher pH value, the polymer presence does not influence the system durability. It is related to the steric and electrosteric stabilization of the colloidal particles by the adsorbed polyvinyl alcohol macromolecules.

The poly(vinyl alcohol) (PVA) influence on the adsorption and electrokinetic properties of the mixed oxide Mn _x O _y –SiO₂/polymer solution system was examined. Three oxides differing with the Mn _x O _y contents were applied (0.2; 1 and 3 mmol/g SiO₂, respectively). The PVA with the molecular weight 100 kDa was characterized with the acetate groups content equal to 14 %. Adsorption, solid surface charge and zeta potential measurements were made as a function of solution pH (3–10). The obtained results showed that the PVA adsorption amount strongly depends on not only the solution pH, but also manganese oxide content on the mixed oxide surface. The higher solution pH value (or Mn _x O _y content) is, the higher polymer adsorption is obtained. The PVA addition to the solid suspension causes minimal changes of the mixed oxide surface charge density, whereas the zeta potential of solid particles increases significantly in the polymer presence.