Defence in the field of engineering physics, Maja Vuckovac, M.Sc.
Exploring liquid droplet behaviour on water-repellent surfaces
Maja Vuckovac, M.Sc., will defend the dissertation "Dynamics of Superhydrophobic Surfaces" on 8 February 2018 at 12 noon at the Aalto University School of Science, lecture hall E, Otakaari 1, Espoo. From the fundamental point of view, this thesis presents an improved understanding of wetting and drop interaction with micro/nanostructures of superhydrophobic surfaces. On the other hand, from the practical point of view, it presents the implementation of these surfaces for viscosity-enhanced drop transport through capillaries as well as mapping of spatial wetting inhomogeneity with extraordinary precision.
Superhydrophobic surfaces are highly water-repellent and shed drops very easily due to their chemical hydrophobicity combined with surface roughness. In the nature, we can find the most prominent example, e.g. lotus leaf, bird feather and butterfly wings. Many intriguing properties of such surfaces originate from the ability of these coatings to support a metastable air layer between the solid and liquid phases leading to fast drop motion with low friction, hydrodynamic slip, and low adhesion. Therefore, there is a wealth of phenomena in this area interesting for physicists.
In this dissertation, the author combines the experimental techniques with analytical modelling and numerical simulations in order to investigate dynamical drop interactions with superhydrophobic surfaces. Firstly was studied the optimization process for synthesis superhydrophobic copper surfaces by measuring dissipation energies and friction forces. The results show that desired sample homogeneity can be obtained using simple fabrication method and served as a starting point for further development of defect-free superhydrophobic surfaces. Next was studied the novel phenomenon of viscosity-enhanced drop motion in superhydrophobic capillaries in tubular geometry. This work not only shows significant viscous flow enhancement, but it also offers insights into new avenues for improving the performance of self-cleaning surfaces and highlights the importance of aerodynamics of the air layer in tubular geometries that are a key component in microfluidics devices. In final part of the thesis was developed a new technique, scanning droplet adhesion microscopy, able to measure small adhesion forces between water drop and superhydrophobic surface with remarkable sensitivity three orders of magnitude higher compared to state-of-the-art techniques allowing to quantify precisely wetting variations on the surface in the form of wetting maps. The results of this work will promote the development of these surfaces by enabling the exploration of microstructure-property relationships.
In general, the understandings obtained in this thesis show the potential for new surface engineering approaches to improve the performance of superhydrophobic surfaces in the wide range of their applications.
Dissertation release (pdf)
Opponent: Prof. Dr. Hans-Jürgen Butt, Max Planck Institute for Polymer Research, Germany
Custos: Professor Robin Ras, Aalto University School of Science, Department of Applied Physics