Presentation Date: Feb 14, 2026
AGSA Abstract
Interfacial water at solid–liquid interfaces plays a central role in catalysis, electrochemistry, and separation science. However, current experimental techniques used to characterize interfacial water structure often rely on ensemble-averaged measurements, which can obscure nanoscale heterogeneity in molecular ordering. As a result, the influence of surface defects and chemical heterogeneities on interfacial water structure, particularly beyond the first solvation layer remains poorly understood. Here, we employ nanoscale Fourier transform infrared spectroscopy (nano-FTIR) to investigate spatially heterogeneous ordering of interfacial water at chemically complex solid-liquid interfaces. By confining broadband infrared excitation to a metallic scanning probe tip, nano-FTIR overcomes the diffraction limit and enables hyperspectral chemical imaging with nanoscale spatial resolution and sensitivity extending tens of nanometers into the aqueous phase through a solid window. Using this approach, we probe variations in the interfacial water H–O–H bending mode as a function of surface chemistry and hydrodynamic conditions, revealing measurable changes in molecular ordering that extend beyond the immediate interfacial layer. When combined with higher-order harmonic demodulation, nano-FTIR provides enhanced sensitivity to interfacial regions while retaining access to subsurface solvation layers inaccessible to conventional surface-specific spectroscopies. Importantly, the observed spectral changes reflect alterations in interfacial water structure rather than bulk-averaged behavior, as demonstrated by flow-dependent modulation of the bending mode response. These results suggest the existence of an intermediate interfacial region that is distinct from both bulk water and the first solvation layer, and which has been largely inaccessible to prior spectroscopic techniques. The study demonstrates a general framework to resolve and understand the complex interfacial water environments at the nanoscale, which are critical to the chemical phenomena at the interface. In addition, this work establishes a new experimental framework for resolving spatially heterogeneous and depth-sensitive interfacial water environments at solid–liquid interfaces.
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