Understanding the Behavior of Sodium Polyacrylate in Suspensions of Silica and Monovalent Salts

This study investigated the interaction of monovalent cations with different sizes on quartz surfaces and the rheological impact that this causes in concentrated suspensions when subjected to the action of a rheological modifier, in this case, sodium polyacrylate (NaPA). Yield stress was determined using a rheometer with a vane-in-cup configuration to establish the relationship between shear stress and strain. Experiments were carried out in LiCl, NaCl, KCl, and CsCl solutions. The results show that the yield stress increases following the order Li < Na < K < Cs in the absence of PAA. However, the addition of NaPA significantly reduced the yield stress in all cases. This reduction was more noticeable in the LiCl and NaCl solutions than in the KCl and CsCl solutions, suggesting a more pronounced effect of PA in maker salts. We conducted molecular dynamics simulations to understand how PA interacts with dissolved salts on the quartz surface. Our results showed that Li had the highest adsorption, followed by Na, K, and Cs. As the salt concentration increased, so did the adsorption. We validated these simulation results with rheological experiments, which helped us understand the observed differences. The molecular interactions indicate that, in the lithium system, cationic bridges and the synergy between hydrogen bridges and hydrophobic bridges predominate mainly. This tendency decreases as the type of cation is changed due to the decrease in the electrical density of the cation in the following order: Li < Na < K < Cs. This reduces bridging with the quartz surface and, therefore, directly impacts the system's rheological properties.