This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A research team from Toyohashi University of Technology, the Institute for Molecular Science and the Institute of Science Tokyo, led by Yu Kinjo and professor Ryugo Tero of Toyohashi University of Technology, has developed a new method to investigate the state of water near material surfaces using X-rays. By combining X-ray absorption spectroscopy with data analysis, the researchers separated the weak signals of interfacial water from those of the much larger amount of surrounding water.
They also revealed differences in the state of interfacial water between inorganic material surfaces and lipid bilayers that mimic biological membranes. This method is expected to contribute to understanding various phenomena occurring at interfaces between materials and water. The study was published online in Applied Physics Express on Oct. 1, 2026.
Water is essential for our daily lives and biological activities. Near the surfaces of materials in contact with water, water molecules can exhibit structures and properties different from those of ordinary liquid water due to their interactions with the materials. Such water is called "interfacial water" and plays important roles in various phenomena, including molecular adsorption onto materials, chemical reactions and biological molecular functions.
Investigating the state of interfacial water at the molecular level is important for understanding material properties and biological processes. One method for investigating the state of water molecules is X-ray absorption spectroscopy (XAS). This technique uses X-rays to probe the electronic states of water molecules and their surrounding hydrogen-bonding environments by measuring how much X-ray radiation is absorbed at different energies.
However, interfacial water near material surfaces accounts for only a small fraction of the total water. Consequently, in conventional measurements, its weak signal is overwhelmed by that of the much larger amount of ordinary water, known as bulk water, making it difficult to extract information specifically from interfacial water. To overcome this difficulty, the research team developed a method that combines X-ray absorption measurements at different water-layer thicknesses with numerical data analysis.
Using a liquid sample cell, the researchers varied the thickness of the water layer through which the X-rays passed. As the water layer becomes thicker, the amount of bulk water increases, whereas the amount of interfacial water near the material surface remains nearly constant. By taking advantage of this difference, the researchers measured a series of X-ray absorption spectra at different water-layer thicknesses.
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