Iwona Ostolska

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.

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.

The impact of polymer structure on the adsorption of ionic polyamino acid homopolymers and their diblock copolymers on colloidal chromium(III) oxide

The aim of the presented study was to investigate the influence of the structure and ionic nature of polymers on the adsorption layer architecture. Chromium(III) oxide was used as an adsorbent. The surface behaviour with the addition of different polyamino acids or polyethylene glycol diblock copolymers was analyzed as a function of the solution pH. The analysis of the data obtained from the adsorption and electrokinetic measurements allowed for the proposal of the most probable structures of the polymer adsorption layers found at the solid particle–aqueous polymer solution interface. Moreover, the application of stability measurements enabled the determination of the interactions between the system constituents. Additionally, investigating the architecture of the adsorbed polymer chains on the solid particles is essential for the further applications of the studied macromolecular compounds.

Adsorption and Stability Properties of Aqueous Suspension of Chromium (III) Oxide in the Presence of Synthetic and Natural Polymers: Possibilities of Solid Removal

The effects of type and content of polymer functional groups on the adsorption mechanism on the chromium (III) oxide surface were studied. Both synthetic [poly(acrylic acid) (PAA), anionic polyacrylamide (PAM), poly(aspartic acid) (ASP), block co-polymer of ASP with poly(ethylene glycol) (ASP-b-PEG)] and natural [bovine serum albumin, ovalbumin, human serum albumin, bacterial polysaccharide (exopolysaccharide EPS)] polymers were applied. For this purpose, adsorption, surface charge, zeta potential and stability measurements were carried out. The largest adsorption was found for the ASP-b-PEG (synthetic polymer) and EPS (natural polymer). The most effective destabilizers for Cr2O3 removal from the aqueous suspension were PAA 240,000 and ASP 6800.

Impact of adsorption of poly(aspartic acid) and its copolymers with polyethylene glycol on thermal characteristic of Cr2O3

Abstract The polymer structure impact on the adsorption layer conformation formed on the chromium (III) oxide surface was investigated. As adsorbates, three macromolecular compounds were tested: poly(l-aspartic acid) homopolymer and two block copolymers containing the poly(amino acid) segments as well as the poly(ethylene glycol) ones in the chain structure. Due to the ionic nature of the poly(amino acid), all measurements were carried out as a function of solution pH value. The most probable polymer chain binding mechanism was determined on the basis of the values obtained from the adsorption, potentiometric titration, turbidimetry and thermogravimetry experiments. The acquired results indicate that the solution pH has a great influence on the adsorbed macromolecule conformation. Additionally, in the case of the block copolymers, the individual structural unit affinity for the solid particles can be modified by the pH changes. Therefore, a significant difference in the mass decrement measured for the systems at pH 3 and 10 can be explained by the contribution of electrostatic forces and hydrogen bond formation to the polymer adsorption mechanism. Structure of the adsorbed polymer layer determines also the suspension stability. The solid surface charge neutralization by the macromolecules bound to the Cr2O3 surface at pH 3 impairs the sample stability, whereas the presence of the extended polymer chains in the basic solution leads to the durability improvement.

Influence of Solution pH on the Nanostructure of Adsorption Layer of Selected Ionic Polyamino Acids and Their Copolymers at the Solid-Liquid Interface

Polymers adsorption at the solid–liquid interface is a very sophisticated process depending on various factors, but at the same time this phenomenon finds numerous applications in many industrial branches as well as in human activities (Wiśniewska et al. React Funct Polym 72:791–798, 2012). The interactions between the adsorbent and the particular copolymer blocks are decisive for macromolecular substance binding on the solid particles surface. The structure of the polymer adsorption layer formed at the solid–liquid interface also depends on the forces present between the segments belonging to different macromolecules. As a result, complex aggregates may be formed on the solid surface (Louget et al. J Colloid Interface Sci 359:413–422, 2011). Additionally, the key role in the ionic copolymers adsorption phenomena is played by the solution pH, which affects the binding mechanism (Hoogeveen et al. Faraday Discuss 98:161–172, 1994).

Influence of the Electrolyte Type on the Adsorption and Electrokinetic Properties of the Ionic Polyamino Acids – Cr2O3 System

Abstract The influence of a kind of support electrolyte on the ionic polyamino acids adsorption at the chromium (III) oxide – polymer solution interface was investigated. The NaCl and CaCl2 were used as the background electrolytes. In order to determine the effect of the electrolyte, the same value of ionic strength of the test solutions were taken. It was proved that formation of intermolecular and intramolecular complexes in the presence of divalent calcium ions is responsible for essential changes in polymer adsorption. Related to the ionic character of polyamino acid two different adsorption behaviours can be observed. The increase of the ASP adsorption amount in the presence of calcium ions may be explained by formation of complexes between the dissociated carboxylic groups and Ca2+ ions. The opposite situation takes place in the case of polylysine – the application of CaCl2 results in the dramatic decrease in the polymer adsorption caused by blocking the active sites available for LYS macromolecules. In order to make a comprehensive analysis, the zeta potential and surface charge density measurements were performed taking into account the kind of the background electrolyte. The above-mentioned tests were carried out in the absence and presence of the polyamino acid at two different concentrations – 10 and 100 ppm respectively.