Photografting of perfluoroalkanes onto polyethylene surfaces via azide/nitrene chemistry

Significance Statement

Hydrophobic surfaces are needed for an array of applications, for instance, as water, dirt and oil repellant outfit of polymeric materials. Polyethylene is a common plastic with a range of uses. Therefore, the current study focuses on modifying polyethylene surfaces to become strongly hydrophobic. Above all, the hydrophobicity must be resistant to abrasion.

Polyethylene is an interesting polymer since it only consists of carbo-hydrogen and carbon-carbon bonds making it quite inert and challenging to modify. In case polyethylene surfaces are rendered permanently hydrophobic, then other plastics can be treated similarly. Perfluorinated alkyl chains possess high water and oil repellency making them good candidates for hydrophobic surfaces. The main aim, therefore, is to graft polyethylene with perfluorinated alkyl chains.

The desired oleophobic and hydrophobic effects can be attained by a highly water repellent perfluorinated carbon chain. This chain must be attached to the perfluorophenyl azide so that to obtain a photo reactive surface modifier. Therefore, researchers at Zurich University of Applied Sciences focused on developing strongly and permanently hydrophobic polyethylene surfaces. They chose polyethylene owing to its unique and model character. Photografting was adopted as a grafting method. Their work is now published in Applied Surface Science.

A photo reactive surface modifier consists of three segments: The azide as the reactive group, which upon activation splits off dinitrogen forming a highly reactive nitrene intermediate that is able to insert into a C-H bond of the polyethylene substrate. The aromatic moiety serves as antenna for the UV-light, activating the azide, and the perfluoroalkane is responsible for the hydrophobic effect. Synthesis of the photoreactive surface modifiers is described. In two steps, starting from commercially available compounds, the modifiers were prepared in high yield and purity. The synthesis is simple, efficient and clean. The preparation of the surface modifiers can easily be scaled up.

Steady-state photo physical investigations showed that the photoreactive surface modifiers possess a strong absorbance in the UV at 266 nm wavelength, and some of them crystallize when brought onto a quartz surface.

The authors were able to come with four fluorinated compounds that were characterized to serve as photo reactive surface modifiers when photografted to polyethylene. The four compounds were photografted to polyethylene. They also determined the water contact angle as well as the surface’s fluorine concentration on the grafted polyethylene and was found to correlate linearly for low coverage.

The researchers performed abrasion and solubility tests on the photografted polyethylene. Washing with acetone exhibited ambiguous outcomes. The surface concentration of the grafted surface modifier decreased with time and didn’t reach a steady state. Abrasion results indicated sufficient abrasion resistance of all the grafted surface modifiers when compared to results of surfaces coated with long chain perfluoroalkene. An abrasion model was developed. This study found that the larger the photo grafted surface modifier, the higher the abrasion resistance.

Photografting of perfluoroalkanes onto polyethylene surfaces via azide/nitrene chemistry

About The Author

Diego Villamaina obtained his Bachelor in Chemistry at University of Perugia, Italy in 2005 and his Master in Physical Chemistry at University of Bologna, Italy in 2008. After that he got involved in a 6 months project at Dublin City University, Ireland working on the synthesis and characterization of dyes used for cellular imaging. He started a PhD in Ultrafast Laser Spectroscopy at the University of Geneva, Switzerland, in the lab of Prof. Eric Vauthey. He studied photo-induced reactions in liquid solution, on a solid state and in prototype devices for solar-energy conversion until 2014. He then did a Postdoc at ETH Zürich, in the field of photoelectron spectroscopy. During this time he became interested in developing computational tools and software for scientific data processing and visualization. In the same area he also worked at ZHAW in Winterthur, and in the private sector.

He is now responsible for the IT infrastructure and development of computational frameworks for interactive visualization and distributed analysis of large-scale microscopy image datasets in the group of Prof. Lucas Pelkmans at the University of Zurich.

About The Author

Jan Inauen obtained a certificate of competence as Plastic Technologist from Hürner AG, Switzerland in 2010. In 2014 he earned his Bachelor in machine engineering with focus material and process engineering from Zurich University of Applied Sciences (ZHAW). After completing his Bachelor, he worked as a Scientific Assistant at ZHAW on photografting of perfluoroalkanes onto polyethylene surfaces via azide/nitrene chemistry in the group for Polymeric Coatings.

In 2017 he started working on a project about lightfast pigments. Also in 2017 he was promoted to scientific staff at the Institute of Materials and Process Engineering (IMPE).

About The Author

Konstantin Siegmann earned his diploma in Organic Chemistry from the Swiss Federal Institute of Technology (ETH Zurich) in 1984. After completing his PhD at ETH with Prof. L. M. Venanzi with a thesis on organo-platinum complexes in 1989, he was awarded a grant for a Post-Doc in Prof. B. H. Lipshutz’ group at the University of California Santa Barbara, where he worked on unsymmetrical biaryl couplings. In 1992 he joined the Laboratory for Combustion Aerosols and Suspended Particles at ETH Zurich and completed his Habilitation with a thesis titled: Nano-Particles in Gas Suspension.

Since 2006 he works at the former Zürcher Hochschule Winterthur (which later became the Zurich University of Applied Sciences, ZHAW) as Senior Scientist and researches in the field of Polymeric Coatings at the Institute of Materials and Process Engineering (IMPE). Konstantin Siegmann’s professional interests are, for example, monomolecular coatings, biocidal coatings, icephobic coatings and other functional coatings. He is author of over 50 scientific papers and inventor of 6 patents.

About The Author

Martin Winkler received his diploma in Chemistry from the University of Konstanz, Germany, in 1994, and his PhD from the same University in 2000. From 2001 – 2007 he was project manager in research and development at Industrielack AG, Lachen, Switzerland. From 2007 – 2010 he led the development of paper and coating at Landqart AG, Landquart, Switzerland. He then became scientific advisor for innovation at Petroplast Vinora AG, Switzerland until 2012.

Since then he is senior lecturer and head of the Laboratory of Polymeric Coatings at the Institute of Materials and Process Engineering (IMPE) at the Zurich University of Applied Sciences (ZHAW). Martin Winkler teaches undergraduate courses in general and organic chemistry, as well as lectures on polymeric coatings.

His focus areas in research are: lacquer technology, coatings technology, sol-gel chemistry, functional surfaces, surface modifications and adhesion promotion.

Reference

Konstantin Siegmann, Jan Inauen, Diego Villamaina, Martin Winkler. Photografting of perfluoroalkanes onto polyethylene surfaces via azide/nitrene chemistry. Applied Surface Science, volume 396 (2017), pages 672–680.

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