Effect of solution pH on the stability of mixed silica -alumina suspension in the presence of polyacrylic acid (PAA) with different molecular weights

Influence of water-soluble nonionic polymers adsorption on colloidal properties of nanosilica dispersions

The relationships between the adsorption of poly(vinyl alcohol) (PVA), poly(ethylene oxide) (PEO), and poly(vinyl pyrrolidone) (PVP) of various molecular weights onto nanosilica and the stability and rheological properties of the aqueous dispersions were analyzed. The adsorption isotherms for the polymers correspond to the Langmuir-type isotherms. The adsorption maximum slightly increases with increasing molecular weight of the polymers. The sedimentation and aggregative stability of the silica dispersion decreased at a low amount of an adsorbed polymer (less than a monolayer). At this polymer content, a significant increase in the viscosity of dispersions is observed due to the formation of polymeric bridges between silica nanoparticles from neighboring aggregates of them. If the amount of adsorbed polymer exceeds the monolayer then the stabilizing effect is observed due to the steric factor preventing the bridge formation and the viscosity of dispersion decreases slightly compared with systems with a low polymer content.

Comparison of stability properties of poly(acrylic acid) adsorbed on the surface of silica, alumina and mixed silica-alumina nanoparticles — application of turbidimetry method

The influence of anionic poly(acrylic acid) — PAA addition on the stability of synthesized silica, alumina and mixed silica-alumina suspensions as a function of solution pH was studied. The turbidimetry method was used to monitor the changes of the examined systems stability over time. The calculated stability coefficients enabled estimation of polymer adsorption influence on stability of metal oxide suspension. It was shown that the alumina suspension without the polymer is the most unstable at the pH values 6 and 9, whereas the silica polymer was most unstable at pH 3. PAA with higher molecular weight (240 000) is a relatively effective stabilizer of all investigated adsorbents (except silica at pH 3). These properties of poly(acrylic acid) are highly desirable in many branches of industry (e.g. production of cosmetics, pharmaceuticals, paints) where polymers are widely used as effective stabilizers of colloidal suspensions.

Comparison of adsorption affinity of polyacrylic acid for surfaces of mixed silica-alumina

The influence of solution pH (in the range 3–9) on the adsorption of polyacrylic acid (PAA) on the mixed silica–alumina surface (SA-3: SiO₂ 97 %–Al₂O₃ 3 % and SA-96: SiO₂ 4 %–Al₂O₃ 96 %) was investigated. The following methods were applied in experiments: spectrophotometry, viscosimetry, potentiometric titration, and microelectrophoresis, which enable determination of adsorbed amount of the polymer, thickness of its adsorption layers, surface charge density, and zeta potential of solid particles in the presence and absence of PAA, respectively. The obtained results indicate that rise of solution pH causes the decrease of PAA adsorption and the increase of its adsorption layer thickness on surfaces of both solids. Moreover, significantly higher adsorption of polyacrylic acid was obtained on the SA-96 surface. This is a result of more favorable electrostatic interactions occurring between the adsorbing polymer chains and the SA-96 surface and formation of a greater number of adsorbate-adsorbent connections through hydrogen bridges.