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In this thesis, the use of femtosecond laser surface processing (FLSP) to enhance the anti-icing properties of a commonly used aircraft alloy, Al 7075-O Clad is described. By changing the surface morphology through FLSP and the surface chemistry through siloxane vapor deposition, the wettability of Al 7075-O Clad was altered.
Condensation and the subsequent freezing of condensates on FLSP Al 7075-O Clad was studied. Both structure height and surface wettability were shown to play a role in the delay of freezing. Freezing occurred on the FLSP superhydrophilic surface faster than on the unprocessed Al 7075-O Clad surface, however, freezing was delayed for all superhydrophobic FLSP surfaces. Tall structure height FLSP functionalized surfaces delayed freezing time longer than short structure height FLSP functionalized surfaces although all were superhydrophobic. It was shown that FLSP functionalized surfaces were able to delay freezing by up to 530 seconds compared to unprocessed Al 7075-O Clad. Self-propelled condensate jumping on FLSP surfaces occurs during the condensing process. The self-propelled jumping phenomena provides a means to promote anti-icing of materials, especially where jumping drops can be swept away in flow conditions
The dynamics of supercooled water droplet impact onto FLSP and unprocessed surfaces was also studied. Imaging of supercooled water droplet interaction dynamics on a solid Al 7075-O Clad cold substrate for a droplet diameter below 160 µm is shown for the first time. Results indicate that microscale supercooled water droplets at low velocities will stick and freeze to unprocessed Al 7075-O Clad surfaces, while FLSP surfaces will repel droplets under similar conditions. A method for estimating the cooling of small falling water droplets in an environment of about -16 °C is described. This method gives insights for determining the temperature of supercooled droplets for the range of droplet diameters used in the experimental studies included in this paper. In addition, a way to estimate the nucleation site of a supercooled droplet by extrapolation of dendrite front velocity is provided.
Advisor: Dennis Alexander