The interactions between six kinds of water-soluble polymers, polyacrylic acid (PAA), polymethacrylic acid (PMAA), acrylic acid-methyl acrylate copolymer [P(AA-co-MAE)], acrylic acid-2- hydroxypropyl acrylate copolymer [P(AA-co-HPA)], hydrolyzed polymaleic anhydride (HPMA) and acrylic acid-maleic acid copolymer [P(AA-co-MA)] and anhydrite crystal have been simulated by molecular dynamics (MD). The results show that the order of binding energy for the six polymers with anhydrite crystal is as follows: P(AA-co-MA)＞HPMA＞P(AA-co-HPA)＞P(AA-co-MAE)＞PMAA＞PAA, and no distinct difference appears between the scale inhibition efficiencies of the same polymer against two crystal faces of the anhydrite. The analysis of various interactions and pair correlation functions of all systems indicates that binding energies are mainly determined by Coulomb interaction. The polymers were deformed during their combination with anhydrite crystal faces, but all the deformation energies were far less than the respective nonbonding energies. The dynamic behaviors of the carboxyls located in different positions of polymer chains are widely different. The carboxyls at the end of chains oscillate more rapidly than those in the middle, so the middle ones hinder the growth of scale crystal more effectively than end segments because they combine with the anhydrite crystal more firmly.

Key words: molecular dynamics, water-soluble polymer, anhydrite, scale inhibitor, binding energy, pair correlation function, deformation energy