concluded that the isolated silanol groups act as the principal Adsorption of poly(ethylene oxide) (PEO) on various oxides adsorption sites for PEO. The silica-PEO interaction was and the flocculation behavior of PEO-coated particles was investibelieved to be through a hydrogen bonding mechanism ingated to elucidate the polymer adsorption mechanism(s). It was volving the isolated surface hydroxyls and the ether oxygen determined that strong Bronsted acid sites on the surface interact of the PEO molecule. with the ether oxygen of PEO, a Lewis base, to induce adsorption Hydrogen bonding has generally been assumed to be a and subsequent flocculation of the substrate particles. In general ubiquitous mechanism of polymer adsorption on hydrophilic highly acidic oxides of the type MO 3 , M 2 O 5 , and MO 2 are expected surfaces. Since isolated surface hydroxyls also constitute the to adsorb and flocculate with PEO. Accordingly, MoO 3 , V 2 O 5 , and surface of other oxides such as alumina, titania, and iron SiO 2 were found to strongly adsorb PEO and exhibit flocculation.
On the other hand, no significant adsorption was observed on oxide, interactions similar to that with silica can be expected oxides with a point of zero charge (pzc) greater than that of silica to cause PEO adsorption. However, Shah found negligible such as TiO 2 , Fe 2 O 3 , Al 2 O 3 -and MgO thereby indicating specificity adsorption of PEO on alumina compared to quartz (5). In of PEO-surface bonding site interactions. The other possible a later study, Koksal et al. (6) suggested that the nonfloccumechanisms of PEO adsorption such as complexation with adlation of alumina and hematite with PEO was due to the sorbed ions and electrostatic interactions with a positively charged lack of accessibility of the polymer molecules to the oxide surface were found not to play a major role in the PEO adsorption surfaces. A similar argument was also proposed by Greenonto oxide particles. In this investigation, the adsorption and flocland to explain the unreactivity of aluminol and silanol surculation behavior of oxides with PEO and the underlying adsorpfaces toward PVA (7, 8). tion mechanism(s) are discussed.