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Thin Film Group's tiny composites research has big industry impacts

News International-French

26 May 2015

The Thin Film Coatings Group at The University of South Australia follow the motto innovation with application. They're a rare breed of research team whose core aim is to collaborate with industry on useful, value-adding techniques and technology.

The group focuses on materials science and surface engineering, with an eye on designing for manufacture. Past collaborations include developing the world's first plastic automotive mirror with SMR Technologies, which is now in mass production.

In October last year, Zuber received the Best Paper Award at the AutoCRC 3rd Technical Conference for his work on transparent hydrophobic coatings for automotive windows - nanocomposites that repel water.

"The concept of hydrophobic or water-repelling coatings is not entirely new. There are products like sprays you can apply on a surface temporarily. Some people have also developed technologies that allow them to apply similar coatings under a vacuum environment."

The difference in Zuber's research is making a permanent coating for transparent materials that can be applied under atmospheric pressure. While the practicality of that might not be immediately obvious, it has far reaching implications.

It could eliminate the need for windscreen wipers, which in turn would eliminate the need for glass windscreens. Lighter plastic windscreens would also require less reinforcement in car bodies, meaning cheaper cars and better fuel economy.

That kind of practical endgame is where interesting meets up with meaningful.

"In our work we always try to look for applications of materials we develop, so in the development process, we always look at ways to make these materials in ways that could be easier to transfer for industrial processes."

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The ability to apply coatings under atmospheric pressure allows for many more materials to be trialled - not everything can stand up to a vacuum. In addition, the whole process is very fast and applies the materials in a single step, critical for an efficient manufacturing environment.

"There are two ways to achieve a hydrophobic or superhydrophobic surface. Firstly, you have to have the right chemistry for your coating. Some chemical groups such as hydrocarbons or fluorocarbons are known to produce hydrophobic properties," Zuber explains.

"Then, making the material or coating rougher enhances the hydrophobic properties. To produce a super-hydrophobic coating, you need to have a combination of both."

Zuber tested a number of coatings under conditions that a car windscreen would typically encounter. In some cases, a superhydrophobic coating performed worse than a less hydrophobic surface.

At a cruising speed of 50 km/h, water droplets are pinned to the surface of a superhydrophobic surface, whereas the airflow over a hydrophobic surface produces enough drag to remove the water.

Rougher surfaces also scatter more light, which dramatically decreases the visibility through a windscreen. A lot of Zuber's work focused on finding a balance.

"The golden point in optical materials is not necessarily to go super hydrophobic with very rough materials, but to find a point between, with no haze.

"Tuning the properties to get them robust also takes some time. Most of these hydrophobic materials are reasonably soft. In my work I started using siloxanes which are materials similar to glass. They are transparent and hard, but can produce hydrophobic properties."

Zuber outlines several methods of synthesising siloxane coatings. They include vulcanisation, sol-gel formulation, thermal and UV curing of siloxane resins, and Plasma Enhanced Chemical Vapour Deposition (PECVD).

The last seems the most promising according to Zuber - PECVD processes allow rapid, one step deposition of nanocomposite coatings of PTFE powder (a fluoropolymer) in a siloxane matrix.

"Some deposition processes we use are already in use in industry in larger scales. In this particular example of my work, it could also be transferred. Basically I developed my materials using atmospheric plasmas. Such systems are maybe not very common, but they are found on an industrial scale."

Of course, more research needs to be done before plastic hydrophobic windscreens can be widely made and used in the automotive industry. Zuber's paper was just one part of his PhD project and provided an initial exploration of the idea, which can be expanded upon if industry partners require it.

Even with a limited scope, he quickly identified the potential of the concept - as well as its issues. While water is no problem for the coatings, condensation and ice provide their own challenges. In addition, it doesn't wholly replace the ability of windscreen wipers to clean dirt from a windscreen, though hydrophobic materials are easier to clean than their counterparts.

In this case, the research doesn't just focus on the scientific details of chemicals and manufacturing techniques, but possible solutions to design hurdles: perhaps a standard windscreen washer can blast contaminants from the surface.

"Developing any product is a very challenging process, but if it was easy, probably someone else would have done it. We have strong experience in this process - our group has examples of successful development," Zuber says.

"That could also be a possible way for the Australian economy, not just to focus on resources, but look at high-tech, high-value products that could solve big problems of high labour costs in the country."

The Thin Film Coatings Group is also a good example of why industry and research cooperation holds so much potential - in fact, why it's a necessity.

"Working on new things gives you a cutting edge in marketing. You develop a brand new product that no one else has on the market, and that gives you great advantages.

"If you don't do it - well, look at Nokia. They weren't so innovative as other mobile phone brands. If you don't move forward, in fact you're going back, because everyone else gets ahead of you."

The intense focus of the research is another indicator of its value. Permanent transparent coatings on an optical surface have plenty of interesting applications beyond windscreens - imagine a pair of spectacles that never got wet or dirty - but the strong direction ties research to more practical, meaningful opportunities, in this case driven by industry supporters SMR Technologies and the AutoCRC.