MechE Colloquium: Making and measuring the most slippery water-repellent surfaces
Event details
| Date | 24.02.2026 |
| Hour | 12:00 › 13:00 |
| Speaker | Prof. Robin Ras, Department of Applied Physics, Aalto University |
| Location | Online |
| Category | Conferences - Seminars |
| Event Language | English |
Abstract: Water-repellent surfaces have the attractive property of staying dry, and find applications in self-cleaning, anti-icing, anti-fogging and much more. These surfaces stay dry because water droplets experience low friction and slide off easily at low tilt angles.[1]
Surface heterogeneity is generally acknowledged as the major cause of contact angle hysteresis and friction of droplets. Here we evaluate this long-standing premise for chemical heterogeneity at the molecular length scale. It is often assumed that achieving low sliding angles on water-repellent surfaces requires hydrophobicity, in other words high water contact angle like for example teflon. We challenge this assumption and demonstrate a hydrophilic alkyltrichlorosilane self-assembled monolayer featuring the unusual combination of low sliding angle and low contact angle. By coating a nanotextured surface with hydrophobic self-assembled monolayer, we obtain extraordinarily low droplet friction.[2]
A major bottleneck to real-world applications of superhydrophobic surfaces has been their fragility. By suitable design of surface textures, we demonstrate extreme mechanical durability of superhydrophobic surfaces.[3]
Finally, because contact angle goniometry has inherent limitations in accuracy [4], we have developed highly sensitive methods to study droplet friction and adhesion.[5,6]
References
1. L. Chen, S. Huang, R. H. A. Ras, X. Tian, Omniphobic liquid-like surfaces, Nature Chemistry Reviews, (2023) 123-137. https://doi.org/10.1038/s41570-022-00455-w
2. S. Lepikko, Y. Morais Jaques, M. Junaid, M. Backholm, J. Lahtinen, J. Julin, V. Jokinen, T. Sajavaara, M. Sammalkorpi, A. S. Foster, R. H. A. Ras, Droplet slipperiness despite surface heterogeneity at molecular scale, Nature Chemistry (2024). https://doi.org/10.1038/s41557-023-01346-3
3. Wang D., Sun Q., Hokkanen M.J., Zhang C., Lin F.-Y., Liu Q., Zhu S.-P., Zhou T., Chang Q., He B., Zhou Q., Chen L., Wang Z., Ras R.H.A., Deng X., Design of Robust Superhydrophobic Surfaces, Nature 582, 55–59 (2020). https://www.nature.com/articles/s41586-020-2331-8
4. Liu K., Vuckovac M., Latikka M., Huhtamäki T., Ras R.H.A., Improving surface-wetting characterization, Science 363, 1147−1148 (2019). https://doi.org/10.1126/science.aav5388
5. Liimatainen V., Vuckovac M., Jokinen V., Sariola V., Hokkanen M., Zhou Q., Ras R.H.A., Mapping microscale wetting variations on biological and synthetic water-repellent surfaces, Nature Communications 8, 1798 (2017). http://dx.doi.org/10.1038/s41467-017-01510-7
6. Daniel D., Vuckovac M., Backholm M., Latikka M., Karyappa R., Koh X. Q., Timonen J. V. I., Tomczak N., Ras R. H. A., Probing surface wetting across multiple force, length and time scales, Communications Physics 6, 152 (2023). https://doi.org/10.1038/s42005-023-01268-z
Biography: Robin Ras heads the Soft Matter and Wetting research group at Department of Applied Physics, Aalto University (Finland). His research area is situated at the interface between physics, chemistry and materials science, dealing with fundamental scientific problems and technological applications. He has authored over 170 scientific publications. Robin Ras received the ERC Consolidator grant for research on extremely water-repellent surfaces (2017-2022). He received the Anton Paar Research Award for Instrumental Analytics & Characterization (2018) for the invention Scanning Droplet Adhesion Microscopy. He obtained his Ph.D. degree in Bioscience Engineering – Chemistry at the University of Leuven, Belgium in 2003.
Surface heterogeneity is generally acknowledged as the major cause of contact angle hysteresis and friction of droplets. Here we evaluate this long-standing premise for chemical heterogeneity at the molecular length scale. It is often assumed that achieving low sliding angles on water-repellent surfaces requires hydrophobicity, in other words high water contact angle like for example teflon. We challenge this assumption and demonstrate a hydrophilic alkyltrichlorosilane self-assembled monolayer featuring the unusual combination of low sliding angle and low contact angle. By coating a nanotextured surface with hydrophobic self-assembled monolayer, we obtain extraordinarily low droplet friction.[2]
A major bottleneck to real-world applications of superhydrophobic surfaces has been their fragility. By suitable design of surface textures, we demonstrate extreme mechanical durability of superhydrophobic surfaces.[3]
Finally, because contact angle goniometry has inherent limitations in accuracy [4], we have developed highly sensitive methods to study droplet friction and adhesion.[5,6]
References
1. L. Chen, S. Huang, R. H. A. Ras, X. Tian, Omniphobic liquid-like surfaces, Nature Chemistry Reviews, (2023) 123-137. https://doi.org/10.1038/s41570-022-00455-w
2. S. Lepikko, Y. Morais Jaques, M. Junaid, M. Backholm, J. Lahtinen, J. Julin, V. Jokinen, T. Sajavaara, M. Sammalkorpi, A. S. Foster, R. H. A. Ras, Droplet slipperiness despite surface heterogeneity at molecular scale, Nature Chemistry (2024). https://doi.org/10.1038/s41557-023-01346-3
3. Wang D., Sun Q., Hokkanen M.J., Zhang C., Lin F.-Y., Liu Q., Zhu S.-P., Zhou T., Chang Q., He B., Zhou Q., Chen L., Wang Z., Ras R.H.A., Deng X., Design of Robust Superhydrophobic Surfaces, Nature 582, 55–59 (2020). https://www.nature.com/articles/s41586-020-2331-8
4. Liu K., Vuckovac M., Latikka M., Huhtamäki T., Ras R.H.A., Improving surface-wetting characterization, Science 363, 1147−1148 (2019). https://doi.org/10.1126/science.aav5388
5. Liimatainen V., Vuckovac M., Jokinen V., Sariola V., Hokkanen M., Zhou Q., Ras R.H.A., Mapping microscale wetting variations on biological and synthetic water-repellent surfaces, Nature Communications 8, 1798 (2017). http://dx.doi.org/10.1038/s41467-017-01510-7
6. Daniel D., Vuckovac M., Backholm M., Latikka M., Karyappa R., Koh X. Q., Timonen J. V. I., Tomczak N., Ras R. H. A., Probing surface wetting across multiple force, length and time scales, Communications Physics 6, 152 (2023). https://doi.org/10.1038/s42005-023-01268-z
Biography: Robin Ras heads the Soft Matter and Wetting research group at Department of Applied Physics, Aalto University (Finland). His research area is situated at the interface between physics, chemistry and materials science, dealing with fundamental scientific problems and technological applications. He has authored over 170 scientific publications. Robin Ras received the ERC Consolidator grant for research on extremely water-repellent surfaces (2017-2022). He received the Anton Paar Research Award for Instrumental Analytics & Characterization (2018) for the invention Scanning Droplet Adhesion Microscopy. He obtained his Ph.D. degree in Bioscience Engineering – Chemistry at the University of Leuven, Belgium in 2003.
Practical information
- General public
- Free