Unveiling DNAPLs solubilization mechanisms: How hydrophobic chain length governs characteristics in novel sugar-based Gemini surfactants.

Surfactant-enhanced aquifer remediation (SEAR) is an effective strategy for removing dense non-aqueous phase liquids (DNAPLs) from contaminated groundwater. While Gemini surfactants possess unique dimeric structures and excellent physicochemical properties, the role of hydrophobic chain length in governing their solubilization performance has not been systematically clarified. Here, five sugar-based anionic-nonionic Gemini surfactants (SANG 06, 08, 09, 10, and 13) with different hydrophobic chain lengths were synthesized and evaluated. The surface activity, hydrophilic-lipophilic balance, and micellar behaviors were characterized, and the relationship between chain length and DNAPL solubilization was systematically investigated. Results showed that increasing hydrophobic chain length significantly influenced micelle formation and solubilization behavior. Among them, SANG 13, with the longest chain, exhibited the most favorable characteristics, including an extremely low critical micelle concentration (0.086 g/L), an optimal HLB value (16.85), and ultra-low interfacial tension with PCE (0.6 mN/m). It also formed the largest micelles (26.80 nm) and the highest aggregation number (Nagg=15.98 at 10 CMC), resulting in superior solubilization and desorption efficiencies for DNAPLs. This study provides the first systematic evidence of how hydrophobic chain length regulates the physicochemical properties and solubilization mechanisms of Gemini surfactants. The findings offer new insights into surfactant structure-function relationships and provide theoretical support for optimizing SEAR technology in DNAPLs-contaminated groundwater remediation.