S. Chibowski

Study of electrokinetic properties and structure of adsorbed layers of polyacrylic acid and polyacrylamide at Fe2O3-polymer solution interface

Abstract Influence of polyacrylic acid (PAA) and polyacrylamide (PAM) molecular weight on adsorption and electrokinetic properties of Fe2O3–polyelectrolyte solution interface was studied. Main factors, responsible for observed changes of zeta potential and surface charge of hematite, were determined on the basic of obtained data. It was demonstrated that number and the distribution of COOH groups in PAA and PAM macromolecules decides on the polymer chain conformation at the interface and directly influences of the adsorption amount of both polyelectrolytes. Using zeta potential the free energies of adsorption of PAA and PAM on surface of Fe2O3 were determined. The thickness of polymer adsorbed layers were calculated basing on measurements of the suspension viscosity, compared to viscosity of polymer solution. It was proved that adsorption layer thickness increases with the increase of the polymer molecular weight, pH and concentration of the polymer solution. Using Scheutjens–Fleer model of polymer adsorption the participation of segments as trains, loops, tails was computed. From the above data a structure of adsorbed polymer layers was proposed. The comparison of determined values of diffuse layer charge with surface charge allow learn main factors responsible for zeta potential changes as a function of polymer molecular weight, pH and concentration of the polymer solution.

Investigation of the influence of the polyvinyl alcohol adsorption on the electrical properties of Al2O3–solution interface, thickness of the adsorption layers of PVA

Abstract The influence of acetate groups contained in polyvinyl alcohol (PVA) and its molecular weight on the electrical properties of the Al 2 O 3 –polymer solution interface were examined. The main factors, having influence on the zeta potential and surface charge changes of Al 2 O 3 , were learned. It was shown that the change of the ion structure in the Stern layer depends considerably on the number of acetate groups (degree of hydrolysis) of the PVA macromolecule and on the conformation of the polymer chain. By the comparison of the determined values of the diffuse layer and surface charges a probable mechanism was proposed, leading to zeta potential changes as a function of pH of the solution and PVA molecular weight. The calculated thickness of the adsorption layers of PVA on the surface of Al 2 O 3 confirmed the essential effect of acetate groups of PVA on its conformation at the surface layer of the adsorbent.

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.

Adsorption of polyethyleneimine and polymethacrylic acid onto synthesized hematite.

An influence of different functional groups of polymer, its molecular weight, polydispersity ratio (M(w)/M(n)) and presence of impurities on its adsorption in different pH values (3, 6 and 9) onto synthesized hematite (Fe(2)O(3)) was measured. A structure of adsorbed macromolecules of PMA and PEI was obtained according to S-F theory. Two polymers were used: polymethacrylic acid (PMA) of 6500 and 75,100 molecular weight as well as polyethyleneimine (PEI) 25,000 commercial and fractionated. Electrokinetic properties of the interface oxide-polymer solution (surface charge density and zeta potential) were also measured as well as adsorption layer thicknesses (with use of viscosimetric measurements). Obtained data show, that all above-mentioned factors do influence not only the adsorption process itself but also a surface charge, zeta potential and structure of adsorbed polymer layers on polymer/hematite interface.

Application of the SAXS method and viscometry for determination of the thickness of adsorbed polymer layers at the ZrO2-polymer solution interface.

The authors studied the influence of the molecular weight of polyacrylic acid (PAA) and polyacrylamide (PAM), solution pH and ionic strength, and the background electrolyte type on adsorption and the thickness of polyelectrolyte adsorption layers formed on ZrO(2) surface. Carboxyl groups distributed along PAA and PAM chains were shown to be responsible for their interface conformation, which directly influences the thickness of the adsorbed polyelectrolyte layers. Bonding of macromolecules with solid surface occurs through the hydrogen bridges of these groups. Two methods were applied to determine the PAA and PAM adsorption layer thickness on ZrO(2), i.e., SAXS (small angle X-ray scattering) and viscometry. Despite some limitations of the SAXS method resulting from the relationship between the size of solid pores, polymer molecular weight, and conformation of the adsorbed macromolecule, all obtained SAXS results were very close to those calculated from viscometry data.

Effect of functional groups of polyacrylamide and polyacrylic acid on their adsorption onto TiO2 surface

Fractions of polyacrylamide (PAM) and polyacrylic acid (PAA) of different molecular weights obtained by fractionation of polydisperse samples were investigated. The effect of molecular weight and functional groups of the polymers on their adsorption densities and the surface charge of TiO2 were studied using adsorption and potentiometric titration methods. On the basis of experimental data the probable mechanisms of adsorption of segments of PAM and PAA onto TiO2 surface were suggested. The biggest difference in the adsorption mechanisms for polyacrylamide and polyacrylic acid is observed for the acidic range of pH. Adsorption results of PAM in the plateau range were compared with the quantities calculated from Scheutjens—Fleer theory.

The effect of sorption properties of soil minerals on the vertical migration rate of cesium in soil

The vertical distribution of137Cs is shown for two types of soil: silly loamy “supposed” soil and silly lessive one, slightly eroded, occuring in the vicinity of Lublin (Eastern Poland). Based on the distribution data the vertical migration rates of137Cs are calculated for both soils. These rates are found to be 0.045 and 0.3 cm/year respectively. The percent contribution of137Cs originating from the damaged reactor in Chernobyl is also calculated. The kinetics of cesium adsorption and its adsorption isotherms on minerals separated from the tested soils are also studied. The sorption of Cs on soil minerals markedly affects the migration rate of137Cs in soil. The experimental results indicate that, among the extracted mineral fractions, the largest adsorption takes place on marls from the silly loamy soil. This work is supplemented by results of a physicochemical analysis of the studied soils.

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.

Competitive adsorption of Ca2+ and Zn(II) ions at monodispersed SiO2/electrolyte solution interface

A study of competitive adsorption of Ca(2+) and Zn(II) ions at the monodispersed SiO(2)/electrolyte solution interface is presented. Influence of ionic strength, pH, and presence of other ions on adsorption of Ca(2+) and Zn(II) in the mentioned system are investigated. zeta potential, surface charge density, adsorption density, pH(50%), and DeltapH(10-90%) parameters for different concentrations of carrying electrolyte and adsorbed ions are also presented. A high concentration of zinc ions shifts the adsorption edge of Ca(2+) ions adsorbed from solutions with a low initial concentration at the SiO(2)/NaClO(4) solution interface to the higher pH values. This effect disappears with a concentration increase of calcium ions. The presence of Ca(2+) ions in the system slightly affects the adsorption of zinc ions on SiO(2), shifting the adsorption edge toward lower pH values and thereby increasing the adsorption slope.

Study of interaction of proteins with fumed silica in aqueous suspensions by adsorption and photon correlation spectroscopy methods.

The interaction of fumed silica A-300 (S(BET) = 297 m2 g(-1)) with bovine serum albumin (prepared by different methods), ovalbumin, human hemoglobin, and gelatin as a function of pH, salinity, and concentrations of components in aqueous medium was studied by adsorption and photon correlation spectroscopy (PCS) methods. Comparison of equilibrium (incubation time t(i) approximately 1 h) adsorption of proteins on A-300, minute (t(i) approximately 1 min) flocculation rate, and the particle size distributions measured by the PCS method shows different rearrangement of particle swarms depending on pH, salinity, and concentration of proteins, especially at pH close to IEP of silica or proteins. The electrokinetic mobility of protein/silica swarms is greater than that of individual components at pH far from the IEP of proteins. Changes in the Gibbs free energy (DeltaG) on protein adsorption depend on pH (-DeltaG is minimal at pH 2, close to the IEP of silica, and maximal at pH between the IEP of protein and silica), concentration (-DeltaG is maximal at C(p) between 1 and 6 mg/ml), type of proteins, and their preparation technique.