Abstract
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.
Highlights
The presence of the macromolecular compounds has a significant influence on the colloidal system stability
In order to determine the polymer adsorption influence on the aqueous suspension stability, the following macromolecular compounds from the polyamino acid group were used as the adsorbates:
Changes in the zeta potential in the presence of polymer may be caused by three different effects involving the following:
Summary
The presence of the macromolecular compounds has a significant influence on the colloidal system stability. The adsorption of polymers (natural or synthetic) at the solid–liquid interface is a very sophisticated process determined by many factors such as macromolecule structure, solution pH, temperature, and surface properties of the adsorbent. Polymer chain presence on the solid surface modifies the stability of aqueous suspensions causing increase of their stabilization (steric, electrosteric stabilization) or a complete destabilization (bridging flocculation, depletion interactions, or charge neutralization) [1, 2]. Determination on which of the phenomena has a dominant influence on the studied system behavior is essential in many areas of human activity, where the aqueous suspensions of various solids are used on a large scale. The destabilization of colloidal systems due to the polymer addition is crucial for the purification of drinking water and mineral flotation processes [3–7]
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