Specific Hydration on p-Nitroaniline Crystal Studied by Atomic Force Microscopy

The molecular-scale structure of water was studied over the (101) surface of p -nitroaniline crystals using advanced atomic force microscopy. p -Nitroaniline contains two polar groups on opposite ends of the nonpolar benzene ring and presents a surface of controlled heterogeneity. The cross-sectional distribution of force applied to the tip was precisely determined and was related to the local density of the structured water. Force modulations were present on the polar end-groups and absent on the benzene ring, suggesting water localization on the polar end-groups.