Water leakage in subsurface structures like tunnels, mines, and oil wells poses significant safety and economic risks. Acrylamide-based copolymers, chemically crosslinked with agents like N,N'-Methylene bisacrylamide (MBA), provide a high-performance solution for controlling such leaks. These polymers form the core of modern water shutoff grouting materials, leveraging controllable gelation and exceptional permeability reduction capabilities. Their unique chemistry and tunable properties make them indispensable for infrastructure protection and resource extraction.  

 1. Chemical Foundations and Polymerization  

Acrylamide (AM) monomers copolymerize with crosslinkers like MBA through free-radical polymerization, typically initiated by potassium persulfate. MBA’s dual vinyl groups create bridges between polyacrylamide chains, transforming the solution into a three-dimensional hydrogel network. Critical variables include:  

- Crosslinker concentration (0.04–0.06% MBA relative to monomers): Optimizes gel elasticity and pore structure.  

- Monomer ratios: Acrylic acid/acrylamide blends enhance ionic strength and swelling.  

- Additives: Clays like bentonite (up to 13%) or kaolin reinforce mechanical strength and thermal stability.  

Reactions occur in aqueous solutions, producing injectable pre-gel mixtures that solidify in situ under ambient temperatures.  

 2. Water-Blocking Mechanisms  

When injected into fractures or high-permeability zones, these formulations undergo targeted gelation:  

- Permeability-guided flow: Low-viscosity solutions penetrate leak paths before crosslinking.  

- Temperature-triggered setting: Subsurface heat accelerates gel formation, creating flexible but resilient seals within 40 minutes.  

- Swelling-driven sealing: Hydrogels expand 390x in water, physically blocking pores and reducing hydraulic conductivity by >90%. This combats both seepage and pressurized water inflows in applications from tunnel stabilization to oilfield conformance control.  

 3. Performance-Enhancing Modifications  

To overcome salinity sensitivity or mechanical degradation, composite designs integrate:  

- Clay-polymer synergy: Bentonite improves water retention and reusability while lowering costs.  

- Saline resistance: Hydrolyzed acrylamide-acrylic acid copolymers maintain >83 g/g absorption even in 0.9% NaCl solutions.  

- Durability enhancements: Surface crosslinking with agents like ethylene glycol diglycidyl ether extends service life beyond 15 years.  

 4. Field Applications and Advantages  

These grouts are used globally for:  

- Oil/gas reservoirs: Diverting floodwater from high-permeability zones to boost oil recovery.  

- Civil engineering: Stabilizing soils and sealing leaks in underground structures like subways or dams.  

- Mine safety: Controlling groundwater influx in shafts or tailings dams.  

Key advantages over cement or silicates include:  

- Adaptive rheology: Flows into micron-scale fractures before gelling.  

- Elasticity: Accommodates subsurface shifts without cracking.  

- Environmental compatibility: Low-toxicity formulations degrade into organic byproducts.  

 5. Sustainability and Future Outlook  

The evolution toward biohybrid systems—like N-succinyl chitosan-g-poly(AM-co-AA)—enhances biodegradability while retaining high absorption. Research focuses on:  

- Smart responsiveness: pH/temperature-triggered gelation for precision deployment.  

- Recycled material use: Integrating waste-derived clays or starches to reduce costs.  

- Long-term stability: Minimizing syneresis (water expulsion) in mature gels through optimized crosslink density.  

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> Acrylamide copolymers exemplify how molecular engineering solves macroscopic challenges. By transforming fluid flows into stable gels, these materials protect infrastructure, conserve water, and enhance resource efficiency—proving that some of the strongest barriers begin as dissolved chains.  

This technology leverages Acrylamide’s reactivity and MBA’s crosslinking efficiency to create hydrogels that balance injectability, durability, and environmental compliance. As water security gains urgency, such customizable polymers will remain vital for sustainable subsurface management.