Surface chemical studies on the competitive adsorption of poly(ethylene glycol) and ammonium poly(methacrylate) onto zirconia

The surface chemical characteristics of zirconia suspension have been examined in the presence of poly(ethylene glycol) (PEG) and ammonium poly(methacrylate) (APMA), both individually and in combination. The adsorption density of APMA for zirconia was found to be higher, compared to that of PEG. In the competitive adsorption studies, the addition of APMA significantly reduced the uptake of PEG onto zirconia, whereas the reverse was not observed. An increase in the electronegative character of the zirconia suspension and shifts in the isoelectric point (IEP) of the zirconia-APMA system were observed, in proportion with the amount of APMA added. However, the zeta potentials of zirconia were not altered in the presence of PEG. The zirconia suspension could be well dispersed over a wide pH range of 5-11, at and beyond 50 ppm addition of APMA. The trends obtained for the dispersion and electrokinetic tests carried out on zirconia, in the combined presence of PEG and APMA, were akin to those of the zirconia-APMA system. Co-precipitation experiments revealed strong complexation between APMA and zirconium species in the pH range of 3-10 in the bulk solution, but in the case of PEG, the interaction was relatively weaker. The adsorption of PEG onto zirconia has been explained to be governed by Lewis acid-base coordination and hydrogen bonding, while in the case of APMA, chemical forces of interaction have been additionally invoked. FT-IR spectral results have provided evidence in support of the proposed interaction mechanisms.