Molecular Dynamics Study of Interaction between Acrylamide Copolymers and Alumina Crystal

Four acrylamide polymer flocculants, anionic polyacrylamide P(AA-co-AM), cationic poly-acrylamide P(DMB-co-AM), nonionic polyacrylamide P(AM), and hydrophobical polyacry-lamide P(OA-co-AM) have been prepared by copolymerizing with acrylic acid, cationic monomer dimethylethyl (acryloxyethyl) ammonium bromide (DMB) and hydrophobical monomer octadecyl acrylate with acrylamide. The interactions between the flocculants withthe (012) surface of alumina crystal (Al₂O₃) have been simulated by molecular dynamics method. All the polymers can bind tightly with Al₂O₃ crystal, the interaction between the O of polymers and Al of the (012) surface of Al₂O₃ is significantly strong. The order of binding energy is as follows: P(DMB-co-AM)>P(OA-co-AM)>P(AA-co-AM)>P(AM), implying a better flocculation performance of P(DMB-co-AM) than the others. Analy-sis indicates that binding energy is mainly determined by Coulomb interaction. Bonds are found between the O atoms of the polymers and the Al atoms of Al₂O₃. The poly-mers' structures deform when they combine with Al₂O₃ crystal, but the deformation en-ergies are low and far less than non-bonding energies. Flocculation experiments in sus-pension medium of 1%Kaolin show a transmittancy of 90.8% for 6 mg/L P(DMB-co-AM) and 73.0% for P(AM). The sequence of flocculation performance of four polymers is P(DMB-co-AM)>P(OA-co-AM)>P(AA-co-AM)>P(AM), which is in excellent agreement with the simulation results of binding energy.