Until the chemistry is right
At Empa, Dorina Opris is researching how to synthesise complex electroactive polymers for robotic components, sensors or batteries - a promising project that the European Research Council is currently funding with one of its prestigious "ERC Consolidator Grants". This is not the Empa chemist's first success - but the road to it was not easy.
The fact that she has mastered her field from A to Z is, as she points out, also thanks to know-how built up by colleagues at Empa – such as engineer Gabor Kovac. He pushed the production of stack actuators with expandable silicone discs for many years and developed them to operational maturity with his partner Lukas Düring until their spin-off “CTsystems” was recently taken over by the Daetwyler Group.
“The devices for measuring how actuators stretch in different electric fields were developed by them,” Opris says, “we were early on this topic, and that helped me enormously.” Unlike her colleagues, however, the chemist is working less on the technology for printing such components, but one “floor below” – on the synthesis of novel polymers that are suitable as non-conductive layers for stacked transistors, elastic films for power generation and other elements.
The desired profile: as thin as possible, with the long-term goal of many layers only ten micrometres thick; easily stretchable, sensitive to low current voltage and robust at the same time. And above all: printable, i.e. without solvents for the conductive layers between which the polymers lie. “Solvents can damage the polymer layers. Besides, the material would have to dry for a long time in order not to give off harmful vapours,” explains Opris, “so we try to do without them – with the right chemistry.”
There are many different requirements that researchers all over the world are dealing with. Suitable compounds that raise hopes are polysiloxanes, which the Empa specialist is also working on. An important advantage of these polymers: they are relatively easy to synthesise; the “backbone” of their strands is very mobile – and they can be specifically manipulated with polar groups, i.e. plus-minus charged molecules.
Snake-like molecules
What is difficult for laypeople to understand, Dorina Opris explains with a vivid image: “You can imagine these polysiloxanes like a pot full of snakes that want to move all the time.” The polar groups have a twofold effect on them. On the one hand, they make the molecular snakes more sensitive to electric fields so that they respond to low voltages. On the other hand, they act like a kind of glue between the molecules; this “stiffens” them and thus reduces the important elasticity. It is necessary to fine-tune both effects to achieve maximum success. For a practical application, the transition from the solid to the elastic state at low temperatures is important so that the technology can later be used at room temperature. In addition, such polymer structures still have to be chemically “cross-linked” so that they can become elastic layers – for example by UV light and with the help of so-called end groups: quasi molecular “hats” that the snakes wear at their ends. But in laboratory practice, it has so far proved tricky to reliably provide these polymers with defined end groups. “That annoys me already!” admits Opris with a smile.
Healthy ambition is needed for the TRANS project, which the chemist herself calls “very, very ambitious”. The team is optimistic because earlier work has already produced encouraging results; for example, a polysiloxane compound that reacted to a voltage of only 300 volts and deformed strongly – an extremely low value. Printing capacitor layers without solvents has also already been achieved. And a doctoral student recently developed a piezo-electric elastomer that, when stretched, shows a significantly higher electrical response than other compounds currently in use.
Creativity and team spirit for success
Of course, many more steps are needed to achieve usable successes – and those qualities that have brought Dorina Opris to Empa and ETH Zurich. Not only stamina and the ability to turn failed attempts into progress, but also to create an inspiring environment for employees that allows open debate and also mistakes so that good ideas emerge.
And above all: optimism. The boss believes that young researchers should be given exciting and challenging projects and then be allowed to work independently so that they remain motivated. Her advice to talented women based on her own biography: “Don’t wait until someone pushes you to do research. You have to be self-motivated and strong, and go for it! And also take a risk sometimes.”