Dirk Hegemann Interview

Greetings from Zurich! It’s travel day for me today, I’m heading to Athens to speak at the iplasmanano conference that starts in a few days. So this is the perfect place to post Dirk Hegemann’s interview. Dirk works at Empa, the Swiss Federal Laboratories for Materials Science and Technology.

Wish I had a longer layover to visit Dirk at his lab! Enjoy his very interesting interview!

Daphne Pappas

 

hegemann-plasma

Dr. Dirk Hegemann, Scientist of the Week

 

1)      What is your personal motto?

“Nil posse creari de nilo” (Lucretius in De Rerum NaturaNatural Science): Nothing can be created from nothing

2)      How much did your mentor influence you?

My mentor during my PhD work and the following years with Fraunhofer IGB was Dr. Christian Oehr, to whom I still have an excellent relationship. I learned from him how to think scientifically and critically. He guided me how to motivate people as well as how to deal with difficult situations. Mainly, I kept the practical approach he pursued: to perform sound science that is also relevant for industry. A prerequisite thus is to know the available literature including older text books.

3)      Describe your latest research work.

One advantage of plasma polymer film growth is its control on the nano scale. Hence, one can play with different layer sequences forming multilayers or vertical gradients. My latest research work deals with hydrophobic-to-hydrophilic vertical gradients: hydrophobic surfaces (i.e. water repellent) which, nonetheless, show water penetration. The resultant hydration of the subsurface induces additional interaction forces on molecules approaching the (still) hydrophobic surface. A better control of adsorption and desorption processes as well as of hydration and evaporation is given – fascinating!

Very recently, I received funding for a PhD work on this topic – thus looking for a PhD candidate.

4)      I consider you a world-renowned expert in the field of Plasma Polymerization. To my knowledge, polymers developed via plasma processing do not possess the structure of chemically grown polymers in the sense that several radicals can contribute to the polymerization process and not a single monomer unit. Based on your expertise and research, do plasma polymers have a promising future for both research and commercialization?

Indeed, small film-forming species determine the film growth in plasma polymerization processes yielding films that are quite different to conventional polymers. Cross-linking of such units during film growth enhances film density and stability, finally yielding hard coatings. Such inorganic “plasma polymers” comprise silica-like (SiOx), diamond-like carbon (DLC) and different nitride (TiN, AlN, CN etc) coatings – nothing in common with polymers. The process is thus often named plasma CVD, but is not different from plasma polymerization. The film properties, however, are entirely controlled by surface processes – its deposition works very well, also in industrial processes.

Functional plasma polymers, on the other hand, require a fine tuning of cross-linking and retention of (e.g. polar) functional groups. Gas phase processes thus become much more important (beside surface processes). Here, current research indicates that the generation of film-forming species, i.e. the plasma chemical reaction pathway, is solely determined by energy per molecule (and, e.g., not by pressure), which is argued for long time and is still up for debate. A minimum set of reactions (typically 1-5) with corresponding rate coefficients would thus be sufficient to describe plasma polymerization (at least the gas phase processes contributing to film growth). The electron energy distribution function, on the other hand, determines the frequency of the reactions taking place. Here, a novel approach for modeling might be possible.

This practical approach so far enables up-scaling and transfer to industry. Among others, we have commercialized ultrathin permanent hydrophilic plasma polymer films used, e.g., for blood filtration.

5)      Several scientists from the Plasma field will read your interview on The Science and Engineering Café. Is there a message that you would like to send to them? Are you interested in new collaborations? Please provide details.

Different communities have different approaches. I like to visit conferences of different communities yet covering the same topic, i.e. Surface Science, Polymer Science, Biointerfaces etc. – which can be very stimulating. Currently, I like to encourage the modeling community to get into discussions about plasma polymerization and possible collaborations.

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