Molecular dynamics study of polyether polyamino methylene phosphonates as an inhibitor of anhydrite crystal

• MD simulation of the interaction of PAPEMP with anhydrite in presence of water
• The interactions with (010) and (020) surfaces of anhydrite show small differences.
• Phosphonate carboxyl oxygen atom and calcium ion form electrovalence bond.
• The number of functional groups and stereo-hindrance effect influence binding energy.

Molecular dynamics (MD) simulations were employed to investigate the interactions between polyether polyamino methylene phosphonate (PAPEMP) with different degrees of polymerization (n = 1–7) and (010), (020) crystal surfaces of anhydrite. An aqueous environment was added through the introduction of water in the simulation cell. The results showed that PAPEMP molecules attach to the surfaces rather than remain in the bulk water and the interactions of the same PAPEMP molecule with the two surfaces show small differences; under the same mass of PAPEMP (n = 1–7), the order of the binding energy Em of PAPEMP is as follows: PAPEMP (n = 3) > PAPEMP (n = 2) > PAPEMP (n = 1) > PAPEMP (n = 4) > PAPEMP (n = 6) > PAPEMP (n = 5) > PAPEMP (n = 7). The number of the functional groups and the stereo-hindrance effect are two main factors influencing the interactions between PAPEMP and anhydrite. When n ≤ 3, the former is the main factor; while n > 3, the latter is the main factor. The binding energies are mainly provided by the ionic bond and the non-bonding interaction. The structures of the polymers are deformed during the combining processes. Simulation results provide theoretical guidance to judge the performance of scale inhibitors, and synthesize new highly effective scale inhibitor.

The MD simulation result of PAPEMP (n = 3) interacting with the (010) surface of anhydrite crystal indicates that PAPEMP molecule has clung to the surface of anhydrite crystal in presence of water after molecular dynamics, which indicates they have attracted each other no matter how the initial configurations of PAPEMP molecules had been laid. For the same mass of PAPEMP(n = 1–7), PAPEMP exhibits different abilities to inhibit the growth of anhydrite in the order of PAPEMP (n = 3) > PAPEMP (n = 2) > PAPEMP (n = 1) > PAPEMP (n = 4) > PAPEMP (n = 6) > PAPEMP (n = 5) > PAPEMP (n = 7).Figure optionsDownload as PowerPoint slide