Effect of functional monomer ratio on the performance of Ni²⁺ coordination-enhanced AA/AM copolymer hydrogels for temporary plugging applications

To address the trade-off between swelling capacity and mechanical strength in conventional temporary plugging hydrogels, the effect of the acrylic acid (AA) and acrylamide (AM) monomer ratio on the Ni²⁺ coordination-crosslinked network and its swelling–mechanical performance was investigated. A Ni²⁺ coordination-enhanced AA/AM copolymer-based hydrogel for temporary plugging applications was prepared via free radical polymerization. The effects of AA/AM monomer ratio on the network structure and the synergistic swelling–mechanical response behavior were systematically investigated by regulating the functional monomer composition. FTIR and XPS analyses confirmed that Ni²⁺ participated in network construction through the formation of dynamic Ni–O coordination bonds with carboxylate groups. On the basis of the copolymer network, an additional ionic crosslinking structure was established, which effectively enhanced the structural integrity and thermal stability of the hydrogel system. With increasing AM content, the swelling ratio of the hydrogel exhibited a non-monotonic variation characterized by an initial increase followed by a subsequent decrease. Meanwhile, a pronounced negative correlation between swelling capacity and compressive strength was observed. This behavior was mainly attributed to the synergistic regulation among coordination crosslinking density, polymer chain flexibility, and chain entanglement degree. By optimizing the monomer composition, a balanced network structure capable of coordinating swelling and mechanical performance was achieved. When the mass ratio of AA to AM was 2∶1, the hydrogel displayed the optimal comprehensive performance. Under 70℃ conditions, the swelling ratio reached 4.469 g·g⁻¹, while the compressive strength after swelling achieved 13 KPa, indicating effective synergistic optimization between water absorption capability and mechanical stability. In addition, the hydrogel exhibited stable rheological behavior and favorable temperature adaptability, demonstrating its suitability for demanding reservoir environments. The developed hydrogel system satisfies the functional requirements of temporary plugging materials, including water absorption and expansion, pressure-bearing plugging, and subsequent degradation or flowback removal. This study provides theoretical guidance for the structural design, performance regulation, and practical development of metal-ion coordination-enhanced polymer hydrogels for temporary plugging applications. These findings provide a theoretical basis for the design and performance regulation of Ni²⁺ coordination-enhanced AA/AM copolymer-based hydrogel.