ADSORPTION OF POLYSTYRENE SULFONATE ON POLYOXYMETHYLENE SINGLE-CRYSTALS AT HIGH IONIC-STRENGTH

The adsorption of polystyrene sulfonate (PSS) from aqueous solution on polyoxymethylene (POM) single crystals has been studied systematically as a function of molecular weight and ionic strength. Substantial adsorption occurs only at high ionic strength, as a consequence of the low affinity of the polyelectrolyte segments for the surface. Adsorption isotherms have a rounded shape. The adsorption increases more or less linearly with increasing ionic strength, and depends strongly upon the molecular weight. From a comparison with adsorption results on hematite and with literature data on other systems, clear trends emerge as to the relation between adsorption characteristics and the affinity of the polyelectrolyte segments for the surface. This affinity may have both electrostatic and nonelectrostatic components. With increasing affinity, isotherms have a more pronounced (pseudo)plateau, the molecular weight dependence is weaker, and the effect of ionic strength is smaller. Desorption experiments showed that the adsorption of PSS on POM is essentially reversible.