On the Origin of Amphiphilic Interfaces

Solid/water interfaces are classified based on macroscopic textbook definitions of hydrophobicity and hydrophilicity. However, at the molecular level, increasing evidence reveals that whether an aqueous interface is hydrophobic or hydrophilic is not a binary question. Outlier interfaces that exhibit both hydrophilic and hydrophobic characteristics keep being dug out at a growing rate. These interfaces are strikingly diverse, ranging from metals to oxides, from conductors to insulators. We show that, despite their diversity, they can be united within a single family of systems with well-identified physical-chemical properties. In analogy to amphiphilic solutes, we name this family "amphiphilic interfaces”. Amphiphilic interfaces possess remarkable wetting and solvation properties, with exciting potential applications in heterogeneous catalysis, geochemistry, nanofluidics, and electrochemistry. To unravel the origin of their atypical behavior, we trace the domain of amphiphilic interfaces as a function of relevant surface properties through extensive molecular dynamics simulations. Our findings elucidate why amphiphilic behavior arises across such a broad spectrum of surfaces, providing a unified framework to rationalize — and in the future control — the many intriguing properties that we keep discovering for these unique systems.