Reload Index (ZRiChK UMCS)
Studies on adsorption properties of ionic and nonionic polymers at metal oxide ‑ solution interface; structure of adsorbed layer.
CHIBOWSKI, Małgorzata WIŚNIEWSKA,
DEPARTMENT OF RADIOCHEMISTRY AND COLLOID CHEMISTRY
Presented studies aimed on determination of the adsorption mechanism of ionic and nonionic polymers at metal oxide-polymer solution interface. Polyvinyl alcohol (PVA) and polyethylene glycol (PEG) were used as nonionic polymers and polyacrylic acid (PAA) and polyacrylamide (PAM) did as ionic ones. As adsorbents were used Al2O3 (for PVA and PEG) and MnO2 and ZrO2 (for PAA and PAM).
A mechanism of the polymer adsorption in presented systems depends on many factors. The most important are molecular weight, degree of hydrolysis and concentration of the polymer, pH and ionic strength of the solution. Meaningful effect has also the presence of surface active compounds (surfactants). The influence of the above on the adsorption and structure of polymers layers forming on the surface of the solid was determined from adsorption measurements and surface charge and dzeta potential of the solid particles. Using viscometry  and SAXS (small angle x-ray scattering)  a thickness of the adsorbed polymer layer on the oxide surface was measured.
Fig. 1. Presents Porod’s plots obtained by SAXS method for ZrO2 with pores filled with water and PAA 2000 and PAA 60 000 solutions.
Fig. 1. Porod’s plots for systems: ZrO2 ‑ water, ZrO2 ‑ PAA 2 000, ZrO2 ‑ PAA 60 000. CPAA = 100ppm, pH = 6, CNaCl = 1´10-2mol/dm3.
As can be seen from the Fig. 1. PAA 2 000 entered ZrO2 pores and formed uniform adsorption layer (well visible negative slope of Porod’s curve vs. q- axis). For this system determination of the adsorption layer was possible. In the case of PAA 60 000 the Porod’s plot is similar to that of ZrO2 ‑ water (line parallel to q-axis). That suggests polymer did not adsorbed inside pores of the solid due to its macromolecule dimensions but rather developed on the surface of ZrO2 particle.
Surfactants also markedly affect the polymer adsorption. The influence of sodium dodecyl sulphate (SDS) on the adsorption of PVA on the surface of Al2O3 is presented on Fig.2.
Fig. 2. PVA adsorption isotherms on Al2O3 surface for the same molecular weight of PVA but various degree of hydrolysis, with and without SDS. CSDS = 1´10-3mol/dm3, CNaCl = 1´10‑3mol/dm3.
Observed changes in terms of adsorbed PVA were explained on the basis of the studies on polymer‑surfactant mutual interactions in water solutions. In the presence of SDS, the increase of PVA and PEG adsorption on the surface of Al2O3 is promoted by forming polymer‑surfactant complexes.
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