Atomic Insight into the Interfacial Effect on the Molecular Solvation

The solvation of amphiphile molecules plays a crucial role in a broad range of physical, chemical, and biological processes. Although we have gained some insights into those processes of bulk solution, the interfacial effects on the molecular solvation are still poorly understood. Here, using qPlus-based noncontact atomic force microscopy, we report the formation of ordered water-methanol clusters composed of hexamers and pentamers on both Cu(110) and Cu(111) surfaces. Interestingly, water and methanol are incompletely mixed on the Cu(110) surface, with methanol residing at the periphery of the water network. In contrast, the amphiphile methanol could be solvated within the water hydrogen-bonding network on the Cu(111) surface, resulting in molecular-scale complete mixing. Density functional theory calculations indicate that the complete mixing is mainly induced by the more facile collective adjustment of the hydrogen-bonding network due to the weaker interaction between the complex and the Cu(111) substrate. This work provides the possibility of fine-tuning the molecular solvation behavior by proper interfacial engineering.