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Research on graphene has made great strides in recent years. However, to fully harness its potential in applications such as desalination membranes, sensors, and energy storage and conversion, a deeper understanding of the interaction between graphene and water is required. Until now, it was widely thought that graphene, when supported on a substrate, largely inherits the wetting properties of the underlying material, a phenomenon known as “wetting transparency.” An international research team led by Yongkang Wang and Yair Litman has now shown that, while graphene appears “transparent” on large scales, it exerts a subtle but significant influence on nearby water molecules at the nanoscale.
Graphene, a carbon layer just one atom thick, is considered a wonder material: extremely stable, highly conductive, and optically transparent. For a long time, it appeared just as transparent to water: measurements of the water contact angle — a measure of wettability — showed that graphene on a substrate “lets through” the substrate’s wettability virtually unchanged. This phenomenon of “wetting transparency,” observed for years, seemed to contradict the fact that graphene is highly polarizable and therefore reacts sensitively to charges in the substrate.
An international team led by Yongkang Wang and Yair Litman at the Max Planck Institute for Polymer Research (MPI-P), in collaboration with the University of Cambridge, the Institute for Basic Science (IBS) in Korea, Korea University, and Durham University, has now closed this gap. The researchers show that, on the micrometer scale, graphene appears transparent to the substrate’s wettability—but on the nanoscale, it significantly reshapes the water structure.
To demonstrate this, they combined advanced surface-specific vibrational spectroscopy with molecular dynamics simulations and studied water on calcium fluoride (CaF2) crystals—once in its pure form and once covered with a single layer of graphene. By varying the water solution pH, they specifically adjusted the surface charge of the CaF₂ and directly tracked how the water near the graphene surface aligns. The result at the macroscopic level: the substrate’s electrostatics dominate the orientation and structure of interfacial water, which remain essentially unchanged with and without graphene—confirming wetting transparency.
However, the simulations reveal what happens at the nanoscale: local charges on the CaF₂ induce corresponding “image charges” in the polarizable graphene layer, shifting graphene’s charges via electrostatic attraction. This alters the strength and direction of the electric field experienced by water molecules in the immediate vicinity. Directly above a local charge in CaF₂, the induced graphene charge can partially shield the field or even reverse it, causing water molecules in the first layer to realign unexpectedly. Just a few angstroms farther away, the field can become stronger than in the absence of graphene polarization, enhancing the alignment of the water molecules.
Averaged over many such charge spots, the opposing local effects cancel each other out—the macroscopic wetting transparency remains intact. Graphene thus acts as a “nanoscale mirror” for substrate charges: it reflects and redistributes them, thereby shaping the water structure without altering the overall macroscopic wetting behavior.
“The observed effects are of high technical relevance,” says Yongkang Wang, group leader in Mischa Bonn’s Molecular Spectroscopy Department. “Rather than merely altering graphene’s surface structure or chemistry, engineers can now consider structuring the substrate charge as a design parameter to control interfacial water.”
Yair Litman, group leader and co- first author of the study, adds: “Controlling graphene’s electronic response with such nanoscale precision could be used to influence ion distributions, water flow, and interfacial reactions.”
This multiscale perspective provides new design rules for applications involving graphene layers in aqueous environments—from nanofluidic membranes to electrochemical energy storage devices and neuromorphic components. In the long term, the targeted use of this new control mechanism at the nanoscale could make graphene membranes more selective, energy storage devices more efficient, and neuromorphic components more robust.
The results were published in the journal “Chem.”
Dr. Yair Litman
+49 06131 379-380
litmany@mpip-mainz.mpg.de
Dr. Yongkang Wang
+49 6131 379-613
wangy3@mpip-mainz.mpg.de
Yongkang Wang, Yair Litman, Minhaeng Cho, Stephen J. Cox, Mischa Bonn
Wetting transparency of graphene across length scales: Macroscopic transparency but nanoscopic mirror-like behavior; Chem (2026) 103023
https://dx.doi.org/10.1016/j.chempr.2026.103023
Using surface-specific vibrational spectroscopy, researchers have solved a long-standing puzzle conc ...
Copyright: © Katharina Maisenbacher / MPI-P
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