Enhancing ultrahigh-temperature resistant performance of fracturing fluid: a dynamically crosslinked hydrogel based on zirconium doped β-cyclodextrin - carbon quantum dots and its rheological properties

To enhance the hydrogel performance under ultra-high temperature conditions, this study developed a novel β-cyclodextrin composite crosslinker (β-CCs) through the synthesis of carbon dots, mono-(6-amino-6-deoxy)-β-cyclodextrin (β-CD), and zirconium oxychloride octahydrate. The β-CCs was subsequently employed to crosslink acrylamide-acrylic acid copolymers (P(AM-AA)), yielding the β-CCs-P(AM-AA) hydrogel. Systematic investigations revealed exceptional thermal stability of the hydrogel, maintaining a viscosity of 122 mPa·s after 147 min of shear treatment at 200°C. Comparative analysis with CDs-crosslink P(AM-AA) hydrogel (without β-CD modification) demonstrated a distinctive secondary crosslinking phenomenon occurring specifically at 100°C in β-CCs-P(AM-AA), attributed to the unique β-CD-zirconium ion chelation mechanism. Rheological characterization at elevated temperatures (80-100°C) combined with post-treatment TEM analysis confirmed that the secondary crosslinking at approximately 100°C significantly reinforced the hydrogel network integrity. This temperature-responsive crosslinking behavior substantially improved the hydrogel's structural stability under extreme thermal conditions. The developed β-CCs-P(AM-AA) hydrogel presents a groundbreaking strategy for designing adaptive polymeric materials capable of functioning in extreme temperature environments, offering new perspectives for high-temperature applications in fields such as enhanced oil recovery and geothermal engineering.