Titanium dioxide isoelectric point

The -potential depends on the pH of the liquid phase. The pH at which the -potential is zero is called the isoelectric point. The isoelectric point of each filler depends on its surface structure. In the case of titanium dioxide, the isoelectric point depends on the surface coating. A Si02 coating decreases the isoelectric point whereas AI2O3 increases it. " ... 

The results of the OWLS experiments (see Figure 3) indicate that the PLL-g-PEG polymer spontaneously adsorbed from a pH 7.4 buffered aqueous solution onto metal oxide surfaces. The example shown in Figure 3 involved the adsorption of PLL-g-PEG onto three different metal oxide surfaces, specifically, titanium, niobium, and silicon/titanium. Tbis adsorption process occurred rapidly and resulted in the formation of a layer of adsorbed polymer on the surface. Typically, for Sio4Tio602 smfaces, a layer with an adsorbed areal density of approximately 125 ng/cm formed, and 95% of the final observed mass was reached within the first 5 min. Similar behavior was observed for the two other metal oxide surfaces investigated (that is, niobium pentoxide and titanium dioxide). Although the adsorption kinetics were quite similar, the resulting amount of PLL-g-PEG adsorbed to the surface was different and depended on the characteristic isoelectric point of the metal oxide, as shown in Figme 4 and Table 4. 37,38,46.48,49... 

Maximal polymer adsorption occurs within a pH range between the isoelectric point of the surface and the pA/a of the polymer. Experiments performed at different pH values, as described in section 2.4.2, showed that negligible PLL-g-PEG adsorption is observed at pH values higher than the pA/a of the polymer (pH 10) or lower than the isoelectric point of the metal oxide surface. The experimental data shown in Figure 7 demonstrate that, for a silicon/titanium dioxide surface, PLL-g-PEG adsorption takes place only in the pH range between 3 and 11. Outside of this range, negligible adsorption is observed. 

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