Technical University of Denmark: Read Rafael Taboryski’s doctoral dissertation online

Professor Rafael Taboryski from DTU Nanolab is inspired by the microstructures of nature, including the surface of the lotus flower’s petals. He has now been awarded a doctorate for his scientific work to recreate similar surface structures.

As a scientist, Rafael Taboryski is interested in the naturally occurring microstructures that exist in the world around us. As an example, he highlights the sacred lotus flower and its petals, which have a self-cleaning surface. Here, water settles like small spherical droplets that absorb the dirt and remove it from the petal when they trickle off.

If you look at the surface of the lotus flower under an electron microscope, you can see that the surface has a particularly granulated and hairy structure. You can also see that the hairs consist of nanofibres with a highly water-repellent chemical composition, which is the secret behind the special properties of this flower.

Precisely the properties you would want on surfaces that are to be easy to clean. In other situations, it may be advantageous for water to settle as a thin film on the surface instead of as small dewdrops. For example, this applies to solar cells, where the efficiency deteriorates if light is dispersed in the droplets.

Amazing properties
“What we do is really just to copy the structures we find in nature and reconstruct them on other surfaces. And we’ve demonstrated that we can actually recreate these amazing properties in plastic, for example.”
Rafael Taboryski
“What we do is really just to copy the structures we find in nature and reconstruct them on other surfaces. And we’ve demonstrated that we can actually recreate these amazing properties in plastic, for example,” says the newly appointed Doctor Technices (Dr.techn.).

Where the lotus flower leaf has a surface that is moisture repellent, the surface of rose petals binds the moisture so that the petal does not dry out. These are primarily the two categories of properties in surface structures with which Rafael Taboryski has worked; microstructures and nanostructures which reject certain liquids or are moistened by them, respectively. Both are about the wetting of surfaces, hence the title of the doctoral dissertation: ‘Engineering of wetting properties for solid surfaces’.

Applicable science
The wetting of solid surfaces is relevant for a wide range of products, from windows to solar cells, glasses, and endoscopes.

Dew consists of a myriad of microscopic droplets which disperse the light and ruin visibility when the surface is cooled below the dew point in a humid atmosphere. An anti-dew effect can be achieved if you can ensure that a thin even—and thus transparent—water film is formed on the surface instead of the micro-droplets. Here the challenge is that the coating must be transparent, and any surface structures must be so small that they do not disperse the light themselves, i.e.—in practice—less than approximately 200 nanometres, equal to about half the smallest wavelength of visible light.

The focus is often on controlling wetting with water such as rainwater on windows or solar cells, but the principles for designing surfaces with well-defined wetting properties are the same regardless of which liquid you are interested in repelling or moistening with.

DTU’s clean room essential to research
Rafael Taboryski is motivated by a desire to understand the world that surrounds us and recreate its microstructures where this makes sense. He has developed methods for design and manufacture of solid surfaces with desired wetting properties and has shown that these properties can be greatly enhanced if the chemical composition of a surface is supplemented by surface structuring on a microscale and nanoscale. The interaction between the chemistry of a surface and its texture is thus the decisive instrument and the key to designing surfaces with very distinctive wetting properties.
An important prerequisite for the work is the unique particle-free clean room facilities found at DTU, where—among other activities—Rafael Taboryski has been able to experiment with plastic instead of having to use more expensive or more difficult materials such as silicon or glass.

The doctoral dissertation is based on 15 publications that he has published in recent years. Together, they represent both a very broad and deep insight into the subject according to Professor Hans Jürgen Butt of the Max Planck Institute in Germany, opponent for the doctoral dissertation.

The work has resulted in many new scientific recognitions as well as collaboration with a number of companies—including Lego and Danapak Flexibles—which work with injection moulded plastic components and plastic films, respectively.

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