Daniel Beitner, MSc Candidate
Highly durable outdoor paints consisting of Polyurethane Acryl based polymers are often used in the automotive and aerospace industries. Controlling the Hydrophilic/Hydrophobic properties of such systems can contribute to better adhesion, self-cleaning and/or anti-icing properties.
Paint samples were coated with either titanium oxide, aluminum oxide or hafnium oxide, using an atomic layer deposition (ALD) process, which produces very thin and uniform coatings with high precision and control. A 16-hexadeconic phosphonic acid self-assembling monolayer (SAM) was also grown on a paint-aluminum oxide substrate, to improve the hydrophilic properties of the substrate.
A weather-o-meter was used to test the coatings’ durability while the change in the wetting angle of the surface of the paint was measured using an optical tensiometer. The change in the paint hue after coating and weathering was measured using a photo spectrophotometer. The chemical qualities and topography of the ALD coating were examined using scanning electron microscopy and time-of-flight scanning ion microscopy. The SAM growth time and quality was measured both by the change of the wetting angle over time, and via in situ weight gain utilizing a quartz micro-balance.
The aluminum oxide coating initially reduced the surface contact angle of the paint from 110 ° to 10 °, but the wetting angle returned to its original values within 24 hours of exposure to air. The addition of the SAM produced a more durable effect: samples coated with SAMs showed an initial decrease of the contact angle to 60-70 °, which persisted even after prolonged weathering.
These experimental results show that the combination of ALD layers and SAMs can produce durable coatings with modified hydrophilic/hydrophobic properties. The use of SAMs with different end-groups may allow fine-tuning of the wetting properties of the coating.
Supervisor: Prof. Boaz Pokroy & Dr. Eric Assouline.