Facet-dependent wettability of Janus Serpentine nanosheets: Direct nanoscale evidence of Amphiphilicity

Facet-dependent wettability is a fundamental yet poorly understood principle governing the stability, aggregation, and performance of 2D Janus materials in diverse separation processes such as oil recovery and pollutants adsorption. However, the direct and quantitative characterization of nanoscale wettability on individual nanosheets remains challenging. Natural serpentine was selected as a representative Janus nanosheet system comprising distinct MgOH, SiO and typical edge facets. A combination of atomic force microscopy (AFM) and extended Derjaguin-Landau-Verwey-Overbeek (EX-DLVO) theory was used to quantitatively characterize the facet-specific hydrophobicity of serpentine nanosheets. Hydrophobic interactions between individual facets and self-assembled monolayers functionalized AFM tips were quantified, followed by EX-DLVO fitting to extract hydrophobic decay lengths. To uncover the molecular origins of facet-dependent wettability, density functional theory (DFT) was performed to evaluate water adsorption configurations and energies. We report the first direct quantification of anisotropic wettability in Janus nanosheets. The MgOH and edge facets were fully hydrophilic, displaying no measurable hydrophobic interaction, consistent with stronger water adsorption energies (−27.62 and − 108.50 kJ mol −1 ). In contrast, the Si O facet exhibited clear hydrophobicity, characterized by hydrophobic decay lengths of 1.00 ± 0.05 nm (pH 5.5) and 1.20 ± 0.05 nm (pH 8.5), which was supported by weaker water adsorption (−18.93 kJ mol −1 ). The insights obtained in this work establish serpentine nanosheets as potential easily exfoliated Janus materials for separation processes involving enhanced oil recovery, emulsion separation, adsorption, and provide guidance for the design of mineral processing reagents.