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Transparent sunlight-activated antifogging metamaterials

Nature Nanotechnology volume 18, pages 137–144 (2023)Cite this article

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Abstract

Counteracting surface fogging to maintain surface transparency is important for a variety of applications including eyewear, windows and displays. Energy-neutral, passive approaches predominantly rely on engineering the surface wettability, but suffer from non-uniformity, contaminant deposition and lack of robustness, all of which substantially degrade durability and performance. Here, guided by nucleation thermodynamics, we design a transparent, sunlight-activated, photothermal coating to inhibit fogging. The metamaterial coating contains a nanoscopically thin percolating gold layer and is most absorptive in the near-infrared range, where half of the sunlight energy resides, thus maintaining visible transparency. The photoinduced heating effect enables sustained and superior fog prevention (4-fold improvement) and removal (3-fold improvement) compared with uncoated samples, and overall impressive performance, indoors and outdoors, even under cloudy conditions. The extreme thinness (~10 nm) of the coating—which can be produced by standard, readily scalable fabrication processes—enables integration beneath other coatings, rendering it durable even on highly compliant substrates.

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Fig. 1: Design and optical properties of the metamaterial coating.
Fig. 2: Structure of the metamaterial coating and angular dispersion relation.
Fig. 3: Experimental set-up and photothermal performance.
Fig. 4: Antifogging performance.
Fig. 5: Defogging performance and real-world feasibility.

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Data availability

All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Information. Figure source data can be found under https://www.research-collection.ethz.ch/handle/20.500.11850/574061 (Iwan Haechler, extended data for ‘Transparent sunlight-activated antifogging metamaterials’, Eidgenössische Technische Hochschule Zurich Research Collection, https://doi.org/10.3929/ethz-b-000574061, 2022).

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Acknowledgements

We acknowledge the support of the cleanroom team at IBM research in Rüschlikon Switzerland, namely R. Stutz, U. Drechsler and A. Olziersky. Further, we acknowledge the technical assistance of L. Steinmann, J. Vidic, H. Albers, C. Germann, D. Trottmann and P. Feusi, all from ETH Zurich. We also acknowledge H. Lambley for help with condensation modelling and imaging, D. Kim for assistance with SEM imaging, the Scientific Center for Optical and Electron Microscopy (ScopeM) and P. Zeng for TEM imaging, H. Park for graphical assistance and fruitful discussions regarding experimental design, R. Ghosh for photocatalytic tests (all from ETH Zurich), Rodenstock Schweiz AG for providing the eyewear and MeteoSwiss for providing meteorological data. This work was financially supported by the Swiss National Science Foundation under grant number 179062 (D.P. and T.M.S.).

Author information

Authors and Affiliations

  1. Laboratory of Thermodynamics in Emerging Technologies, Department of Mechanical and Process Engineering, ETH Zurich, Zurich, Switzerland

    Iwan Haechler, Nicole Ferru, Gabriel Schnoering, Efstratios Mitridis & Dimos Poulikakos

  2. Laboratory for Multiphase Thermofluidics and Surface Nanoengineering, Department of Mechanical and Process Engineering, ETH Zurich, Zurich, Switzerland

    Thomas M. Schutzius

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  1. Iwan Haechler
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Contributions

G.S., T.M.S. and D.P. designed the study and provided scientific guidance throughout. I.H., G.S. and E.M. designed the metamaterial coating. I.H. and N.F. designed the experimental devices. I.H. fabricated samples. I.H. and G.S. characterized the materials. N.F. and I.H. conducted experiments. I.H., N.F. and G.S. analysed the data. I.H., G.S. and D.P. wrote the paper. All authors have read and approved the final version of the paper.

Corresponding authors

Correspondence to Gabriel Schnoering, Thomas M. Schutzius or Dimos Poulikakos.

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Competing interests

A patent has been filed by ETH Zürich and is pending (EP22161807.7: Heating device for preventing or removing a deposition). The inventors are I.H., D.P., G.S., T.M.S. and E.M. The remaining author (N.F.) has no conflict of interest.

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Peer review information

Nature Nanotechnology thanks Zhiguang Guo, Zuankai Wang and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Notes 1–10 and Figs. 1–10.

Supplementary Video 1

Outdoor test in Walenstadt, Switzerland (I0 ≈ 339 W m−2, Tamb ≈ 4 °C, RH ≈ 80%).

Supplementary Video 2

Visibility test in Davos, Switzerland (I0 ≈ 212 W m−2, Tamb ≈ 4 °C, RH ≈ 46%).

Supplementary Video 3

Outdoor test in Davos, Switzerland (I0 ≈ 212 W m−2, Tamb ≈ 4 °C, RH ≈ 46%).

Source data

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Statistical Source Data Fig.2c

Source Data Fig. 3

Statistical Source Data Fig.3b, c

Source Data Fig. 4

Statistical Source Data Fig.4a, c

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Statistical Source Data Fig.5b

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Haechler, I., Ferru, N., Schnoering, G. et al. Transparent sunlight-activated antifogging metamaterials. Nat. Nanotechnol. 18, 137–144 (2023). https://doi.org/10.1038/s41565-022-01267-1

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