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Developing Super-hydrophobic Surfaces

A team from the Sapienza Department of Mechanical and Aerospace Engineering has introduced new principles for the design of super-hydrophobic surfaces that can be used for wide range of technical applications, even in extreme conditions.

The study, which is part of Project “Cavitation Across Scales: Following Bubbles from Inception to Collapse,” funded by the European Research Council, aims to overcome the limits imposed by the fragility of super-hydrophobic surfaces by introducing a new type of surface.

“One of the issues with corrugated hydrophobic surfaces,” explains Simone Meloni, one of the researchers on the team, along with Emanuele Lisi, Matteo Amabili, Alberto Giacomello and Coordinator Carlo Massimo Casciola, “is that if superficial cavities get wet due to sudden change in pressure, temperature or other parameter, they become unusable. Moreover, this issue is further compounded by the irreversible nature of this process. It is not always possible to recreate the air/vapour layer or to recreate it without an external stimulus.”

Materials with corrugated surfaces present nanoscopic imperfections (in the magnitude of a tenth of a millionth of a meter) that can trap air or vapour, reducing the contact area between liquids and solids. These characteristics make the material exceptionally super-hydrophobic that can be employed in a range of technological applications, as for example, blocking the creation of ice on airplane wings, electric cables and wind turbines.

The researchers used computer simulations to develop a new type of cavity: a composite structure with longitudinal channels and 10-20 nanometre-wide square holes that can be used to recreate the air/vapour layer without any external action.

“Engineering geometry through the use of nanotechnology,” concludes Casciola, “allows us to create new functional materials, tools and systems with unique elements deriving from the combination of their chemical and morphological properties. In our case, we developed self-recovery.”

The new surface morphology proposed by the research group, which is defined as “modular texture,” will allow us to solve many issues that have limited the development of super-hydrophobic surfaces: from self-cleaning surfaces (the difficulty for contaminating particles to adhere to the surface in conjunction with the easy flow of water on super-hydrophobic surfaces keeps them clean) to low-friction surfaces for vessels (and corresponding energetic savings), from anti-ice surfaces (with possible applications in aeronautics) to microcondensation materials (i.e., energy scavenging, which is also studied by Casciola’s group).

The results of the study have been published on ACS Nano.