Małgorzata Wiśniewska

Application of the zeta potential measurements to explanation of colloidal Cr2O3 stability mechanism in the presence of the ionic polyamino acids

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.

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.

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.

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.

Removal possibilities of colloidal chromium (III) oxide from water using polyacrylic acid

The lack of water is the most serious threat to humanity that leads to more efficient water and sewage treatment. Currently, many scientists are looking for new coagulants, flocculants and physicochemical methods allowing for sufficient removal of pollutants from water. The presence of various types of pigments, including chromium (III) oxide, poses the major problem. Even small amounts of these substances inhibit life processes in water. In this paper, the stability of Cr2O3 suspension in the absence and the presence of polyacrylic acid (PAA) was determined. To explain the changes in the system stability, the adsorption and electrokinetic measurements were performed. The chromium (III) oxide suspension not containing PAA is the most stable at pH = 3. Under these conditions, each positively charged solid particle is surrounded by a negatively charged diffusion layer which protects from particle collision and aggregates formation (electrostatic stabilization). In turn, the Cr2O3 suspension containing the PAA is most unstable also at pH = 3. In this case, the polymer causes destabilization of the colloidal suspension, which results from charge neutralization of solid particles by adsorbed PAA.

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.

Adsorption and thermal properties of the bovine serum albumin-silicon dioxide system

The adsorption, electrokinetic, thermal and stability properties of the silicon dioxide (silica, SiO2)/bovine serum albumin (BSA) system were determined. All measurements were carried out as a function of solution pH value. The highest amount of BSA absorbed on the silica surface was observed at pH 4.6 [the value close to the BSA isoelectric point (pI)], which is primarily related to the packed albumin conformation and the lack of adsorbent–adsorbate electrostatic repulsion. At pH 4.6, largest mass decrease was also noticed (thermogravimetric measurements). At pH 3, 7.6 and 9, the adsorption levels were much lower. This phenomenon is associated with the electrostatic repulsion between the BSA macromolecules and the silica particles as well as the expanded BSA structure. During biopolymer adsorption, the whole solid surface is coated with the albumin macromolecules. Then, the properties of the silica particles become similar to those of the BSA macromolecules. In the presence of albumin, the silica pHiep point is identical to the BSA pI value. It should also be noted that the albumin adsorption affects the SiO2 suspension stability. The greatest change was observed at pH 3. Under these conditions, the BSA addition causes electrosteric system stabilization.

Study of the Adsorption Mechanism and the Structure of Adsorbed Layers of Polyelectrolytes at the Metal Oxide/Solution Interface

The influence of the molecular weight of polyacrylic acid (PAA) and polyacrylamide (PAM) as well as of inorganic contaminants on the ZrO2 surface on the adsorption and electrokinetic properties of the metal oxide/polyelectrolyte solution interface were studied for ZrO2 and Fe2O3 solid particles. The calculated concentrations of the various surface groups on ZrO2 and Fe2O3 enabled an investigation of the possible mechanism for the bonding of the studied polyelectrolytes with the surfaces of both oxides. PAA and PAM macromolecules bond with the solid surface mainly via the –OH groups of the oxides, which may interact with the carboxy groups of polyelectrolytes through hydrogen bridging. A comparison of the change in values of the diffuse layer charge with the surface charge enabled the principal factors responsible for the changes in the zeta potential of the oxides, e.g. pH, polymer molecular weight and concentration of the polymer solutions, to be evaluated. From such zeta potential values, it was possible to determine the free energies of adsorption of PAA and PAM on the surfaces of both oxides. The thicknesses of adsorbed polymer layers on Fe2O3 and ZrO2 were calculated on the basis of measurements of their suspension viscosities in the absence and presence of adsorbed polymer. It was shown that the thickness of the adsorption layer increased with increasing polymer molecular weight, pH and concentration of the polymer solution. Because the experimental determination of the number and the length of trains, loops and tails in such polyelectrolytes was not possible, the participation of such segments of polymer structure at the interface was computed using the Scheutjens–Fleer model of polymer adsorption. The polymer adsorption expressed as the number of equivalent monolayers was calculated and compared with the experimental data.

Investigation of the colloidal Cr2O3 removal possibilities from aqueous solution using the ionic polyamino acid block copolymers

Disposal of the environmentally dangerous metal oxide suspensions from the waste water is an essential problem. The polymers adsorption can be one of the most effective and suitable methods. In the presented paper the ionic diblock copolymers impact on the Cr2O3 suspensions was investigated. The copolymer adsorption layers structure was determined on the basis of the adsorption and electrokinetic (surface charge density and zeta potential) tests. The polymers adsorption amount was measured using the static method from aqueous solutions. Additionally, the application of the turbidimetric method enabled determination of the interactions between the system constituents. Analysis of this data allows the estimation of the most probable stabilization (or destabilization) mechanism of the Cr2O3 suspensions in the presence of the studied macromolecular compounds. Hence, the Cr2O3 suspensions are unstable in the presence of the anionic copolymer at pH 3 and the cationic one in the alkaline medium.

Influence of Temperature and Purity of Polyacrylic Acid on its Adsorption and Surface Structures at the ZrO2/Polymer Solution Interface

The influence of temperature and the effect of the purity of polyacrylic acid (PAA) on its conformation on the zirconium oxide surface were studied. Spectrophotometric measurements, potentiometric titrations, electro-kinetic and viscosity measurements allowed the determination of the amounts of polymer adsorbed, the surface charge and the zeta potential of solid particles in the absence and presence of the polymer together with the thickness of the polymer adsorption layers. All measurements were carried out over the temperature range 15—40°C. The occurrence of a minimum in the adsorption of PAA between 25–30°C was caused by conformational changes of the polymer macromolecules. For non-filtered PAA, a decrease in polymer adsorption and an increase in the thickness of the adsorbed polymer layers were observed. These result from changes in the polydispersity index of filtered PAA and the blocking of some active sites on the oxide surface by inorganic contamination present in the non-filtered PAA samples. The free energy of PAA adsorption was calculated from the zeta potential data. Some parameters characterizing the conformation of PAA chains in the bulk liquid phase and on the ZrO2 surface were determined.