Public defence in Materials Science, MSc Mehran Mirmohammadi

Title of the thesis: Fabrication of multifunctional superhydrophobic surfaces

Thesis defender: Mehran Mirmohammadi
Opponent: Prof. Kosmas Ellinas, University of the Aegean, Greece
Custos: Prof. Sami Franssila, Aalto University School of Chemical Engineering

Have you noticed how certain vegetables, like leeks or broccoli, repel water during washing? Or wondered how butterflies stay dry in the rain? Nature offers valuable lessons in engineering. This remarkable ability is known as superhydrophobicity, a property that allows surfaces to repel water and stay dry. 

This thesis focuses on the development of multifunctional superhydrophobic surfaces. It investigates a range of fabrication strategies, including replication, lithography, film deposition, and etching, to produce superhydrophobic surfaces that exhibit multiple properties, including conductivity, wetting anisotropy, anti-icing behavior, and antibacterial effects.

Additionally, this thesis examines the durability of superhydrophobic surfaces under mechanical loads, such as abrasion, which significantly impact their anti-wetting properties and, consequently, their lifespan and performance across various applications. It explores various strategies, including the creation of overhanging structures, the shielding of nanostructures with microstructures, and the application of hard coatings to enhance mechanical durability. 

Superhydrophobic materials and surfaces offer multifunctional benefits, including enhanced antibacterial effects. Their nanostructured design minimizes the solid contact area, hindering bacterial adhesion and growth by maintaining a trapped air layer between the surface and bacteria. It demonstrates that combining superhydrophobicity with copper significantly enhances antibacterial properties compared to superhydrophobic-only surfaces and copper-only surfaces, as evidenced by a notable decrease in the number of viable cells. Furthermore, superhydrophobic surfaces exhibit remarkably low ice adhesion, especially in low-humidity conditions during freezing. The air pockets under water droplets slow heat transfer, delay ice formation, and further contribute to their multifunctionality. Surfaces in this thesis exhibit low ice adhesion after a number of icing–shearing cycles; however, after repeated freeze-thaw cycles, some degradation in their properties remained. These results demonstrate that superhydrophobic properties can be integrated into multifunctional surfaces, enabling them to function in practical applications.

Keywords: multifunctional surfaces, robustness, replication, candle soot, plant leaf, anti-icing, antibacterial, superhydrophobicity

Thesis available for public display 7 days prior to the defence at Aaltodoc. 

Contact information: 
mehran.mirmohammadi@aalto.fi