Nanoscale Surface Roughness Induces Long‐Range Ordering of Interfacial Water Over Tens of Molecular Layers

ABSTRACT

Understanding how far solid surfaces influence the structure of adjacent water remains a central challenge in interfacial science. Here, we demonstrate that nanoscale surface roughness can induce long‐range ordering of interfacial water extending over tens of molecular layers under ambient conditions. We develop an attenuated total reflection infrared (ATR‐FTIR) differential spectroscopy strategy that enables quantitative extraction of interfacial water spectra from the overwhelming bulk‐water background and allows simultaneous determination of interfacial water thickness. Applied to TiO ₂ ‐water interfaces, this approach reveals a clear transition in hydrogen‐bond structure: smooth single‐crystal surfaces exhibit moderately strengthened hydrogen bonding similar to bulk water perturbation, whereas rough surfaces generate pronounced low‐frequency O‐H stretching bands characteristic of strongly hydrogen‐bonded, ice‐like networks. Cluster‐based vibrational analysis indicates that these spectral features originate from highly coordinated hydrogen‐bond motifs. Quantitative analysis further shows that interfacial water extends to 23–41 molecular layers on rough TiO ₂ surfaces, significantly exceeding the 11–15 layers observed on smooth crystals. These results provide direct experimental evidence that nanoscale confinement at realistic solid‐liquid interfaces can stabilize extended hydrogen‐bond networks and establish a quantitative framework for probing interfacial water beyond the limits of conventional surface‐sensitive techniques.