Ferroelectric materials: High-performance nylon capacitors

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Nylon isn’t bulky and it “polarizes”. The material has been used to make stockings for around eighty years, and now these properties make the wafer-thin plastic also attractive for wearable, transparent electronics.

Whether it’s a smartphone, smart watch, fitness tracker, or data glasses – these days, it seems that almost no one leaves home without some form of electronics. The next step in the area of wearable electronics are smart clothes, which are still to go mainstream. After all, it would surely be simpler to have at least some of the devices integrated into garments. However, this requires materials that are thin and flexible and that are also equipped with the appropriate electrical properties. Ferroelectric materials have emerged as a suitable solution. When an external electrical field is applied, ferroelectric materials form two poles with different charges, which can be maintained or switched. One of the most important materials with these properties are perovskites. The materials are already used in ceramic capacitors, solar cells, sensors, and ceramic high-temperature superconductors.

It is well known that nylon stockings become electrically charged when they come into contact with other materials. The ancient Greeks discovered what we know as the triboelectric effect more than 2000 years ago by rubbing (tribo  = rub) amber with cat’s fur.

In addition, some nylon types, such as nylon-11, also have ferroelectric properties. But compared to other materials they have the advantage that they can be liquefied with suitable solvents. This allows flexible thin layers to be produced inexpensively, which can then be processed to make electronic components, such as capacitors, transistors, and diodes. As a consequence, ferroelectric polymers are a suitable choice for integration into textiles.

Ferroelectric nylon

To date, this has been used only rarely in electronic devices, since high-quality, thin layers of ferroelectric nylon could not be manufactured using solvent processes.

But now, scientists at the Max Planck Institute for Polymer Research, in collaboration with researchers from the Johannes Gutenberg University Mainz, Germany and the University of Lodz in Poland, have solved this forty-year-old problem and developed a process to manufacture ferroelectric thin film capacitors from nylon. To do this, they dissolved nylon in a mixture of trifluoroacetic acid and acetone and then solidified it again in a vacuum. The resulting nylon layers are typically just a few hundred nanometers thick – in other words, several hundred times thinner than a human hair. With this method it is also possible to produce extremely smooth thin films, which prevents electrical breakdowns of capacitors, for example. Because they are so smooth, the thin films are also transparent, which would allow production of transparent electronic devices.

With their newly developed process, the scientists were able to produce high-performance nylon capacitors, which remained stable even with extended stress cycles with millions of charging and discharging processes. In the future, the thin nylon layers could become an important component for use in flexible electronics and be integrated in foldable electronic devices or for wearable electronics. These new findings also point the direction towards multifunctional textiles, which can be used as a fabric for clothes and also generate electricity through body movement.





Transparent nylon (Image: Frank Keller/MPI-P).

Transparent nylon could be an important building block for the development of transparent electronic circuits in the future.(Image: Frank Keller/MPI-P).