Molecular dynamics simulations of the conformation and diffusion of partially hydrolyzed polyacrylamide in highly saline solutions

Abstract

The impact of salts on partially hydrolyzed polyacrylamide (HPAM) is of great interest in mineral processing, considering that the use of seawater seems to be the only sustainable solution in regions with severe aridity. Here the conformation and transport of an HPAM chain in several saline solutions are studied by means of molecular dynamics simulations. Results indicate that the electrostatic repulsion between anionic acrylate units causes the polymer to adopt diverse and complex expanded tertiary conformations, however in the presence of cations this repulsion is shielded causing the polymer to fold into balled-up conformations. The structure assumed by the HPAM chain depends slightly on the type of cation and much on intramolecular crosslinking. Cations influence the ordering of water structure and orientation of water dipoles reducing the mobility of water, ions, and HPAM. These results are expected to contribute to a better understanding of particle flocculation for sustainable water management.