Novel polyethylene glycol-based cationic Gemini surfactants for enhancing oil displacement efficiency of silica nanoparticles fluids

Although silica nanoparticles (NPs) have demonstrated potential for enhanced oil recovery (EOR), their individual application faces significant limitations including poor dispersion stability and elevated interfacial tension. A polyethylene glycol-bridged Gemini surfactant was synthesized and evaluated for its interfacial and emulsifying properties, with particular emphasis on its ability to enhance the oil displacement efficiency of NPs. FTIR and ¹H NMR characterization confirmed the successful synthesis of the novel Gemini surfactants (PEGnC). The results demonstrated an inverse correlation between critical micelle concentration (CMC) and spacer molecular weight, while interfacial activity was enhanced with increasing brine salinity. PEG6C (600 Da spacer) exhibited superior performance, achieving ultra-low interfacial tension (10⁻²-10⁻³ mN/m) at 15–25 % NaCl concentrations while demonstrating optimal interfacial activity and emulsification capacity. The optimal PEG6C surfactant was subsequently combined with NPs to formulate a stable nanocomposite fluid, which maintained low viscosity and turbidity while achieving significantly reduced interfacial tension, indicating excellent dispersion stability and interfacial activity. The addition of PEG6C to NPs fluids could significantly improve the oil recovery efficiency of NPs fluids from 11.82 % to 30.66 %. This work establishes a promising strategy for combining Gemini surfactants with NPs to develop high-performance EOR systems.