|M.Sc Student||Amsalem Koby|
|Subject||Characterization of Icephobic Polymer-Coated Surfaces|
|Department||Department of Polymer Engineering||Supervisors||Dr. Orna Breuer|
|Professor Emeritus Abraham Marmur|
|Full Thesis text - in Hebrew|
Ice affects many of the infrastructures of our lives, from power lines, wind mills, airplanes etc. Ice formation on different surfaces harms their functioning by increasing aerodynamic drag and increasing weight, and in some cases may be dangerous and cause acute damage. It is known that 58% of wintertime Unmanned Aerial Vehicles (UAVs) flights in the Kosovo civil war had been affected and damaged by icing.
Static tests in an environmental chamber showed that a super-hydrophobic coating over a surface with controlled morphology prevented ice, down to -30ºC. The impact velocity was approximately 12 km/hr.
In dynamic conditions, in an ice tunnel, a large decrease in ice accumulation was achieved, and in some cases ice formation was even prevented. The most significant decrease in ice accumulation was demonstrated on a surface that combines a controlled non-continuous pattern with chemical modifications. On the reference surface a thick and continuous ice layer was accumulated. On the flat treated surface there was a decrease in ice accumulation. A sharp decrease in ice accumulation was achieved by using a combination between a super hydrophobic coating with a non-continuous pattern. In addition, total ice prevention was achieved on treated surfaces with a wing profile geometry. In cases that ice did accumulate on treated surfaces, a relatively high adhesion reduction was demonstrated.
A theoretical analysis of the stability of a super-hydrophobic non-communicating pattern, built of separated cells, was examined when droplets hit it at high velocity. The analysis considered the pattern's geometry, the water's contact angle on the surface, the droplet hitting velocity and the droplet's volume. The equation of state for water droplets impacting the pattern surface was determined using the Young-Laplace equation, a conservation of mass equation and an adiabatic expansion of gas equation. Calculations were executed with MATLAB. The critical parameters to obtain a stable super hydrophobic surface at high impact velocities were found to be the cell's diameter and the water's contact angle on the surface. Another phenomenon was discovered as well, the water penetration into each examined pattern occurred at a certain critical point, i.e. each pattern has its velocity threshold, after passing this velocity, the penetration to the pattern happens rapidly. In conclusion, in the present work, the surface chemistry and morphology of different materials have been characterized. The ability to delay or prevent ice formation from super-cooled droplets was tested by static and dynamic tests. The critical parameters and characteristics of surfaces that have a potential to repel ice were studied. The results of the research, so far, showed that a superhydrophobic coating over a surface with controlled morphology prevents ice, in static conditions, down to -30ºC. In dynamic conditions, in an ice tunnel, a large decrease in ice accumulation was achieved, and in some cases ice formation was even prevented. In cases that ice did indeed accumulate, a relatively high adhesion reduction was demonstrated qualitatively.