Molecular dynamics simulation on the interaction between polymer inhibitors and anhydrite surface

Investigation on the microscopic interaction between polymer inhibitors and calcium sulfate will be helpful for understanding its scale inhibition mechanism and can provide a theoretical guidance to developing new scale inhibitors. In this work, molecular dynamics simulations with COMPASS force field have been performed to simulate the interaction between hydrolyzed polymaleic anhydride (HPMA), polyaspartic acid (PASP), polyepoxysuccinic acid (PESA), polyacrylic acid (PAA) and the (001) and (020) surfaces of anhydrite (AD) crystal with and without water. The results show that the sequence of binding energies between four polymer inhibitors and AD (001) and (020) with water is PESA>PASP>HPMA>PAA. The binding energy of the same polymer inhibitor on AD (001) is smaller than that on AD (020). Water molecules weaken the deformations of HPMA and PAA but aggravate those of PASP and PESA. Natural bond orbital (NBO) charges of the repeat units of polymer inhibitors were calculated by B3LYP/6-31G* method. The Coulomb interaction is formed between the O atoms of polymer inhibitors and the Ca atoms of AD crystal. The system of polymer-AD is mainly contributed from the non-bonding interaction. Polymer inhibitors do not interact directly with AD crystal, but indirectly through the interactions between inhibitor-H2O and H2O-AD, i.e. water molecules participate in scale inhibition of polymer inhibitors to AD crystal. Water molecules cannot be ignored when the interaction models are constructed, i.e. solvent effect cannot be ignored. Copyright (c) 2015 John Wiley & Sons, Ltd.