Influence of the solid type on the adsorption mechanism of nonionic polymers in the metal oxide/water solution system—temperature effect

Abstract

Abstract The main purpose of the study was to determine the effect of adsorbent type (surface characteristics and pore size) on nonionic polymers adsorption mechanism on the solid surface in the temperature range 15–40 °C. Polyethylene glycol (PEG) and polyvinyl alcohol (PVA) were used in the experiments as adsorbates. The following metal oxides were applied: aluminum (III) oxide, silicon (IV) oxide, zirconium (IV) oxide and controlled porosity glass (CPG). Polymer adsorption mechanism and structure of its adsorption layer at the metal oxide-aqueous solution interface were proposed based on the data obtained from the techniques: spectrophotometry, viscometry, microelectrophoresis and potentiometric titration. They allowed the determination of the amount of adsorbed polymer, the linear dimensions of polymer chains in the solution, the thickness of the polymer adsorption layer, the free energy of polymer adsorption and the surface charge density of the adsorbent in the absence and presence of PEG and PVA. It was indicated that the polymer adsorption on the metal oxide surface increases with the rise of temperature. It is caused by conformational changes of adsorbing macromolecules expressed in the increase of linear dimension of polymer chain. Such specific conformation of the macromolecular compound influences the structure of its adsorption layer. Both PEG (containing only hydroxyl groups) and PVA (containing 2% of acetate groups besides hydroxyl ones) show the smallest adsorption on the silica surface. In the case of the other examined oxides, polymers demonstrate different behavior. PEG adsorption is the greatest on the CPG surface, whereas PVA is the highest on the zirconia surface. It can be caused by various pore sizes of the applied metal oxides whose adsorbing PEG and PVA chains are able to penetrate or not (depending on a macromolecule diameter).