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ICEphobicity for severe ICing Environments

Final Report Summary - ICE^2 (ICEphobicity for severe ICing Environments)

The present report briefly summarizes the research project achievements, which are discussed in more details in the two periodic reports for the two periods: 1) September 2012 - November 2013, and 2) November 2013 – November 2014.
• WP1: Supercooled drop impact on dry, pre-wetted and iced surfaces. A new state-of the-art icing apparatus has been developed at LTNT (Laboratory of Thermodynamics in Emerging Technologies) headed by Prof. Poulikakos (scientist in charge), to study impact of supercooled drops in severely supercooling conditions. The problem of supercooled water drops impacting on superhydrophobic textures for drop supercooling down to −17 °C was investigated, to find that increased viscous effects significantly influence all stages of impact dynamics, and in particular, the impact and meniscus impalement behavior, with severe implications to water retention by the textures (sticky versus rebounding drop) and possible icing. In addition, a specific study on liquid meniscus penetration into the microtexture was also performed using X-ray during a test campaign at the Paul Scherrer Institute (Switzerland) synchrotron.

• WP2: Ice crystal impact on dry, pre-wetted and iced surfaces. An innovative drop handling system, based on acoustic levitation, was recently developed, optimized and integrated in the icing apparatus to generate not only extremely supercooled drops, even below -20°C (thus extending the test conditions reached using a classical pendant drop dispenser as developed in WP1), but also ice crystals and ice-liquid mixtures. Impact tests were conducted on superhydrophobic surfaces to observe different scenarios, including ice crystal formation at the moment of impact due to instantaneous nucleation of extremely supercooled drops, as well as inhibition of drop rebound in case of partially frozen drop (i.e. liquid-ice mixture) on superhydrophobic surfaces, identifying that ice crystals can stick to surfaces in the presence of liquid water, due to capillary adhesion effects.

• WP3: Design and production of functionalized surfaces. Together with specific micro- and nano-engineered surfaces, which were specifically designed and fabricated on silicon based surfaces to conduct supercooled drop and ice crystal experiment, the problem of surface durability under adverse conditions was addressed. By superposing selected hydrophobic layers (i.e. self-assembled monolayers, thin films, or nanofibrous coatings) on hierarchically textured aluminum surfaces, a surface that simultaneously exhibit excellent chemical stability, mechanical durability and droplet impalement resistance was developed and fabricated. Additional multi-functional superhydrophobic surfaces were developed using polymer nano-composites, providing to the solid surface not only the non-wetting properties, but also high electrical conductivity.

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