This work aimed to develop SiO 2 nanoparticles functionalized with amine (SiO 2 /amine) to inhibit the chemical degradation of partially hydrolyzed polyacrylamide (HPAM) in the presence of different ionic species through static experiments and molecular simulations. The effect of the SiO 2 /amine on the rheological behavior of HPAM solution was evaluated in the presence of monovalent, divalent, and trivalent cations. To understand the relationships between polymers, ions, and nanostructures, interaction energies and the radii of gyration under all saline scenarios were calculated by molecular dynamics (MD). The SiO 2 /amine was spherical with a size <100 nm. There is a correlation between the ion's valence and the chemical degradation of HPAM: in the presence of polyvalent cations, the viscosity losses of the HPAM solutions reached up to 94%, incorporating SiO 2 /amine at 100 mg L −1 mitigated the viscosity losses by up to 16%. The molecular simulations showed that the self-folding of the HPAM chains increased in brine containing trivalent cations leading to the viscosity loss of the solutions. The presence of SiO 2 /amine increased the radius of gyration of the polymer up to 17%, improving the viscosity of the HPAM solutions. This study opens a broader landscape regarding nanotechnology to improve polymer flooding applied to the oil industry.

The presence of cations on injection fluids used during polymer flooding leads to viscosity losses of the polymeric solution and reduces its drag capacity. Thus, understanding the mechanisms of this chemical degradation is crucial to improving the efficiency of these treatments. This study focused on obtaining physical insights into the mechanisms involved in chemical degradation by molecular dynamics simulations. To do this, the interaction energies between a variety of cations present at polymer flooding (Na + , Ca 2+ , Fe 2+ , and Fe 3+ ) and partially hydrolyzed polyacrylamide (HPAM) were calculated. First, several potentials for ion description were evaluated to guarantee a proper description of the ion hydration. Then, multiple simulations were carried out to understand the effect of each ion individually and the synergic effect of a mixture of ions (brine) on the HPAM chain shrinking. The radius of gyration of the HPAM chain was used as an evaluation parameter of the chain shrinking. The results indicate that multivalent cations have a stronger interaction with the polymer than the monovalent cations, exhibiting smaller interaction distances and higher interaction energies. These interaction energies are related to the ionic radius of the cations and their charge. Smaller cations get close enough to avoid the repulsion between charged monomers, being the Coulombic interactions the most important (two-third of the total interaction energy). Thus, the strongest interaction energies with the HPAM correspond to multivalent cations, which reduce the radius of gyration of the HPAM since they can interact with two carboxylate oxygen simultaneously. Interestingly was found a high dependence of the concentration of Fe 3+ cations in the interaction with HPAM; at high concentrations, the cations cannot get close enough to interact with the polymer, but in low concentrations, the cations present the strongest interaction. These findings contribute to understanding the mechanisms that macroscopically are related to viscosity losses in the solution by the cation effect.