Decoding the biphasic effect of polyacrylamide hydrolysis on solution viscosity

Polyacrylamide is widely used in industrial applications such as enhanced oil recovery and water treatment due to its excellent ability to regulate the rheological properties of solutions. However, during these applications, progressive hydrolysis alters the molecular structure of polyacrylamide, leading to a unique biphasic change in viscosity that remains poorly understood. In this study, density functional theory calculations and molecular dynamics simulations were systematically conducted to elucidate the molecular mechanism of polyacrylamide hydrolysis and clarify the origin of its biphasic viscosity response at molecular level. The density functional theory calculations and molecular dynamics simulation results reveal that initial hydrolysis enhances structural viscosity by promoting polymer aggregation, whereas further hydrolysis leads to polymer chain dispersion, resulting in a decrease in structural viscosity and an increase in frictional viscosity. At high hydrolysis levels, chain recoiling driven by salt ion interactions reduces both structural and frictional viscosities. This study not only elucidates the fundamental mechanisms governing polyacrylamide hydrolysis and its biphasic effects on viscosity but also provides valuable insights for designing polymers with optimized rheological properties to meet the demands of diverse industrial applications.