Effect of salt-resistant monomers on viscosity of modified polymers based on the hydrolyzed poly-acrylamide (HPAM): A molecular dynamics study

Abstract

In this work, the viscosity and the aggregation behavior of partially hydrolyzed poly-acrylamide (HPAM), 2-acryloylamino-2-methyl-1-propanesulfonic acid (AMPS) and acrylamide-N-vinypyrrolidone (AM-NVP) in aqueous solution and salt solutions were investigated by molecular dynamics simulation. The results show that: (i) The order of the viscosity of different polymer solutions is AMPS > HPAM > AM-NVP. With the aggregation and curling of the polymer chains, a spatial network structure among the polymer chains is formed by the occurrence of the intermolecular and intramolecular cross-links through hydrogen bonds, increasing the rigidity of polymer chains. Simultaneously, due to the number of electronegative atoms and steric stabilization, the order of the number of hydrogen bonds in three polymer solutions is AMPS> HPAM> AM-NVP. (ii) The synergistic stabilizing effects of the surrounding cations around different monomers in three polymers can increase the viscosities of three systems, and negatively charged groups tend to be transfer from the inside of polymer chains to the outside of the chains because of the electrostatic attraction, reducing the electrostatic repulsion and maintaining the number of hydrogen bonds. (iii) Different ions (Na+, Mg2+, Ca2+, Cl−) have different effects on the groups of three polymers. For COO− and SO3− groups, Mg2+ basically cannot enter the hydration layer around the groups, while Na+ and Ca2+ can enter the hydration layer of both groups and tend to be distributed between two oxygen atoms. Moreover, Mg2+ and Ca2+ ions have the main influence on the C5H9NO group.