Adsorption-induced remodeling of nanoscale heterogeneity governs the transport of surfactant-modified nanobubbles in porous media

Surfactant-modified nanobubbles (S-NBs) are promising carriers for subsurface remediation, yet their transport in porous media remains insufficiently understood. In this study, the mobility of anionic sodium dodecyl sulfate (SDS)-, cationic cetyltrimethylammonium bromide (CTAB)-, and nonionic Triton X-100 (TX100)-stabilized nanobubbles was systematically evaluated in sand columns under varying groundwater chemistries and media conditions. The transport capacity followed the order SDS-NBs > CTAB-NBs > TX100-NBs > pure NBs. Adsorption of free surfactants on sand altered the interfacial electrical properties and shifted S-NB–collector interactions toward electrostatic repulsion. However, classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory could not explain the lower mobility of CTAB-NBs despite their higher predicted energy barrier relative to SDS-NBs. Straining and surface roughness effects were excluded. Kelvin probe force microscopy and microfluidic visualization showed that surfactant adsorption dynamically remodels nanoscale charge heterogeneity on sand surfaces. SDS preferentially shields positively charged impurity sites, reduces surface heterogeneity, and suppresses localized energy traps, resulting in an effective repulsive barrier stronger than that predicted by DLVO theory. In contrast, CTAB forms hydrophobic hemimicelles that enhance charge heterogeneity and lower the effective barrier to retention. These results identify adsorption-induced remodeling of nanoscale heterogeneity as a key mechanism governing S-NB transport in porous media and provide a basis for screening surfactant formulations for site-specific subsurface delivery.