A new frontier for anti-icing systems

The University of Trento and Bruno Kessler Foundation have joined forces to fund a joint PhD programme to investigate how to slow down the formation of ice on a surface, searching for a way to repel dew microdroplets before they freeze. The team of researchers is made up of Nicolò Giuseppe Di Novo (PhD) and Nicola Pugno from the Laboratory for Bioinspired, Bionic, Nano, Meta Materials & Mechanics of the Department of Civil, Environmental and Mechanical Engineering (Dicam) of UniTrento, and Alvise Bagolini from the Micro Systems Technology unit of the Center for Sensors and Devices at Fbk.
Their work opens up new perspectives in the field of aeronautics and thermodynamic systems. In these areas, understanding how to change the surface properties of a material has a major impact in terms of energy performance, costs and safety. Think of airplanes, wind turbines, heat pumps and refrigeration systems: here, the presence of ice causes problems that, at the moment, have complex solutions which require energy and the use of polluting products. That is why scientists are exploring ways to prevent the formation of ice or to facilitate its removal. This paper is a contribution in that direction.It is known that the presence of millimetric, micrometric or even nanometric roughness and the intrinsic chemical characteristics of materials affect how fluids interact with the surface. The challenge was to control the microdroplets of water that form below zero, before they turn into ice. The researchers have designed and fabricated silicon truncated microcones, covered by uniformly hydrophobic nanostructures.
The dew microdroplets grow by condensation in a confined space, between the cones, separated from each other, and have a stretched, elongated shape. Before turning into ice, they self-propel from the micro-cones, that is, they jump in the air.
The team examined the drop jump and demonstrated that self-ejection slows down the freezing process. All these jumps create a free zone, a sort of ice-cutting trail that slows down frost propagation.
The rapid self-ejection was observed using a high-frame-rate camera coupled with a microscope. The camera took up to 90,000 photos per second.
The result of the study is that divergent structures with uniform wettability facilitate the self-ejection of liquids. And they can be used to design and build anti-icing systems.
"We have structured the silicon surfaces using the same techniques used to produce chips or sensors. The challenge – explains Nicolò Di Novo, currently postdoc researcher at Dicam – is to provide other materials with these properties, such as aluminium, titanium, steel and polymers."
"These super water-repellent surfaces that blow away the drops – adds Nicola Pugno, Professor of Solids and Structural Mechanics at the University of Trento – go far beyond the well-known superhydrophobic surfaces inspired by the lotus effect (that is, the ability of a material, observed on lotus leaves, to keep itself clean). Their design calls for the formulation of new theories and their microfabrication requires state of the art technologies. Finally, these surfaces are potentially very interesting for the high-tech industrial sector, in line with the third mission of our laboratory."
The possible applications of this study also include the aircraft sector. Ice forms on all aircraft that reach a certain altitude, on airplane wings and helicopter blades or wind turbines or space equipment, it is inevitable. Several studies are underway to find quick and economic solutions to this problem. The researchers of UniTrento and Fbk have given their contribution by thinking of a surface that slows down the formation of ice and facilitates its spontaneous detachment. Other applications may be in the design of heat pumps (e.g. in electric cars), industrial chillers, high-voltage transmission lines in mountain areas. These is equipment where fast defrosting ensures functionality.
The study was funded by the European Commission as part of the "Boheme" project, by the European Regional Development Fund and by the Ministry of University and Research through the STREAM Project.
The article "Single condensation droplet self-ejection from divergent structures with uniform wettability", which describes the self-ejection of water droplets, has been published in the journal ACS Nano and is available at https://pubs.acs.org/doi/full/10.1021/acsnano.3c05981
Paper appeared on the front cover of the journal.
A study on anti-frosting surfaces has been published in Advanced Materials Interfaces and is available at: https://onlinelibrary.wiley.com/doi/full/10.1002/admi.202300759