Molecular Dynamics Study of Interaction between Acrylamide Copolymers and Alumina Crystal

Four acrylamide polymer flocculants, anionic polyacrylamide P (AA-co-AM), cationic polyacrylamide P (DMB-co-AM), nonionic polyacrylamide P (AM), and hydrophobical polyacrylamide 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 with the (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 0 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. Analysis 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 polymers' structures deform when they combine with Al2O3 crystal, but the deformation energies are low and far less than non-bonding energies. Flocculation experiments in suspension 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.