Adsorption of PAA on the α-Al₂O₃ surface

The specific system of interest is the polyacrylic acid (PAA) and (0001) α-Al2O3 surface, which was modeled and simulated by Cerius2 4.9 software with empirical potentials. The simulation predicted that the adsorbed conformations of PAA with a molecular weight (Mw) of 5000 were train and tail at pH <4 and >10, respectively. After gradually inserting additional PAA molecular chains, the adsorption reached a saturated amount. Gel permeation chromatography experimental results showed that the adsorption amount at pH 3.6 was three times greater than that at pH 11. Based on the results from simulations and experiments, a successively increasing pH environment was modeled to illustrate the possibility of optimizing electro-steric effects by combining the higher adsorption density at a lower pH and strong steric repulsion of tail-adsorbed configuration at a higher pH.