Teresa Urban

Adsorption and thermodynamic properties of the alumina–polyacrylic acid solution system

Free energies of polyacrylic acid (PAA) adsorption (DeltaG( composite function)) on an alumina (Al(2)O(3)) surface in the temperature range 15-35 degrees C were estimated on the basis of adsorption-desorption measurements of the inorganic radioactive ions (36)Cl, (45)Ca, and (55)Fe. Adsorbing polymer macromolecules caused the desorption process of previously adsorbed radioactive ions. The free energy of Ca-PAA surface complex formation (DeltaG(o)) was estimated to be close to the free energy of Ca(2+) ions adsorption (polymer causes about 50% desorption of these ions). Moreover, a free energy of polymer molecule adsorption increase with the increasing temperature was observed. The obtained values of DeltaG(o) were compared with those calculated from the adsorption data. Additionally, the amount of polymer adsorbed and the thicknesses of polymer adsorption layers were determined in the temperature range 15-35 degrees C. The changes of polymer chain conformation with the temperature increase are responsible for the increase of PAA adsorption as well as thickness of polymer adsorption layers in the studied temperature range.

Impact of polyacrylamide with different contents of carboxyl groups on the chromium (III) oxide adsorption properties in aqueous solution

The main goal of experiments was determination of solution pH and contents of anionic groups in polyacrylamide (PAM) macromolecules on the stability mechanism of chromium (III) oxide suspension. The spectrophotometry, potentiometric titration, microelectrophoresis, viscosimetry and turbidimetry were applied. They enabled determination of polymer adsorbed amount, surface and diffusion charges of solid particles with and without PAM, thickness of polymer adsorption layer, macromolecule dimensions in the solution and stability of the Cr2O3 - polymer systems, respectively. It was found that adsorption of anionic PAM decreases and thickness of polymeric adsorption layer increases with the increasing pH. Slightly higher adsorption was obtained for the PAM samples containing a greater number of carboxyl groups. At pH 3 and 9 insignificant deterioration of stability conditions of Cr2O3 particle covered with polyacrylamide was observed (neutralization of solid positive charge by the adsorbed polymeric chains (pH 3) and single polymeric bridges formation (pH 9)). The electrosteric repulsion between the solid particles covered with PAM layers at pH 6, is the main reason for significant improvement of Cr2O3 suspension stability in the polymer presence.

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.

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

The influence of solution pH (in the range 3–9) on mixed silica-alumina suspension in the absence and presence of polyacrylic acid (PAA) was studied. The composition of the adsorbent was SiO2 (97%) and Al2O3 (3%). The turbidimetry method was applied to record changes in the stability of the investigated systems as a function of time. It was shown that the suspension without the polymer is less stable at pH 3, whereas at pH 6 and 9, the systems were stable. PAA with molecular weights 100 000 and 240 000 at pH 3 (improvement of system stability conditions) and PAA 2 000 at pH 6 (deterioration of suspension stability) have a great effect on the silica-alumina suspension stability. The stabilization-flocculation properties of polyacrylic acid are a result of a specific conformation of its chains on the solid surface where it depends on the solution pH and the polymer molecular weight.

Impact of anionic and cationic polyacrylamide on the stability of aqueous alumina suspension—comparison of adsorption mechanism

In the present study, particular emphasis was put on the effects of the type of functional groups of anionic and cationic polyacrylamide (PAM) and solution pH on the mechanism of polymer adsorption on the surface of dispersed alumina. The polymer-adsorbed amount, surface charge density and zeta potential of solid particles without and with PAM, as well as the stability of Al2O3 suspension containing the polymer, were determined. For this purpose, the spectrophotometry, potentiometric titration, microelectrophoresis and turbidimetry were applied. It was shown that adsorption of anionic PAM decreases with the pH rise, whereas in the case of cationic PAM, it increases. High adsorption level is a result of more coiled structure of adsorbed macromolecules. The anionic PAM has greater impact on the suspension stability deterioration in comparison to the cationic polymer in the whole range of studied pH values. The more pronounced effect of alumina suspension destabilization in the anionic PAM presence was obtained at pH 6, at which solid surface charge neutralization occurs.

Stability of Colloidal Silica Modified by Macromolecular Polyacrylic Acid (PAA) – Application of Turbidymetry Method

The effect of anionic polyacrlic acid (PAA) adsorption on fumed silica (SiO2) surface on suspension stability was studied. The turbidymetry method was applied to monitor the changes in the suspension stability (using apparatus Turbiscan LabExpert with cooling module TLAb Cooler). PAA macromolecules contain dissociable carboxyl groups, therefore, all measurements were carried out at three pH values: 3, 6 and 9. Analysis of obtained transmission and backscattering curves and Turbiscan Stability Indexes (TSI) allowed determination of the most probable mechanism of the stability of the studied systems. The PAA adsorption has the greatest impact on the silica suspension stability at pH 3 (significant improvement of its stability). On the other hand, the presence of polyacrylic acid at pH 6 causes a noticeable deterioration of system stability conditions. At pH 9, polymer minimally influences the stability of SiO2 suspension.

Comparison of adsorption affinity of ionic polyacrylamide for the surfaces of selected metal oxides

The influence of metal oxide type on the adsorption affinity of anionic polyacrylamide for the solid surface was studied. There were selected three metal oxides: chromium(III) oxide, zirconium(IV) oxide and aluminium(III) oxide. The adsorption behaviour of high-molecular weight polymer containing 30% of carboxyl groups was determined based on the results of spectrophotometric, electrokinetic and turbidimetric measurements. The anionic polymer exhibits the greatest adsorption on the surface of chromium(III) oxide whereas PAM affinity for the aluminium(III) oxide is the lowest. The polymer presence has a pronounced impact on the electrokinetic properties of examined suspensions manifesting in changes in pHpzc and pHiep values of PAM-containing systems compared to those without polyacrylamide. The anionic PAM addition at pH 6 has the greatest effect on the stability of metal oxide aqueous suspensions.

The Spectrophotometric Investigation of Nonionic Polymer Adsorption (Polyethylene Glycol (PEG), Polyethylene Oxide (PEO) and Polyvinyl Alcohol (PVA)) Influence on the Alumina Suspension Stability – Effects of Polymer Type, its Molecular Weight and Solution pH

The effect of nonionic polymer adsorption on the stability of alumina (Al2O3) in the pH range 3–9 was examined. The influences of polymer type and its molecular weight, as well as solution pH, were studied. The following macromolecular substances were used: polyethylene glycol (PEG), polyethylene oxide (PEO) and polyvinyl alcohol (PVA). The spectrophotometry method was applied to obtain the stability curves (dependence of suspension absorbance vs. time). The obtained results indicate that the addition of the polymer influences alumina suspension stability. The addition of the polymer at pH 3 improves the stability conditions of investigated systems. At pH = 6 the decrease of Al2O3 suspension stability (except PEG 2 000) was obtained. On the other hand, at pH 9 the presence of polymer improves the stability properties of the alumina. The higher the molecular weight of the polymer, the more pronounced effects were observed. Moreover, adsorption of polyvinyl alcohol whose macromolecules contain ionizable acetate groups causes greater changes in alumina suspension stability in comparison to the systems containing polyethylene glycol and polyethylene oxide.