Researchers at Christian-Albrechts-University of Kiel (CAU) have now found a way to eliminate this additional polarization step. In thejournal *Science*, Dr. Stefan Schröder, who leads an independent research group at Professor Franz Faupel’s chair, demonstrates how his team can polarize certain polymers during their synthesis using initiated chemical vapor deposition (iCVD). This effect was previously unknown.

Surface potential is generated during coating

The discovery was made as part of research on electret thin films. Electrets are materials that generate a permanent electric field—similar to how a refrigerator magnet is permanently magnetic. The team worked with various molecules that are suitable as starting materials for polymer coatings. 

“Actually, at first we just wanted to understand the electrical polarization properties that the molecules we use exhibit on surfaces,” says Schröder. When he and his colleagues used them to produce polymer films and examined their surface potential, they made an unexpected discovery: The layers generated a surface potential of up to 24 volts, even though no one had applied an external electric field beforehand. Apparently, the polymer films had polarized on their own during their fabrication.

“Polarization occurs as early as the coating stage,” explains Schröder. A key factor here is the structure of the molecules used: Their electrical charge is often distributed unevenly, causing them to adopt a specific electrical orientation. 

Polymerization stabilizes the state

The manufacturing process is equally important: Using iCVD, researchers combine these gaseous molecules into a thin layer of macromolecules or polymers. In this particularly gentle process, polarization occurs spontaneously. In contrast, when the same starting materials were processed into polymers by other means—not via gas-phase deposition—the team was unable to observe any electrical potential.

The researchers can specifically control the strength of the resulting surface potential. They are now able to produce layers with potentials of up to 100 volts. These high surface potentials arise in extremely thin coatings: The layers studied by the researchers are only ten nanometers to one micrometer thick and are therefore invisible to the naked eye. The surface potential increases with the thickness of the polymer layer. Schröder and his colleagues were also able to specifically alter the direction of polarization by selecting the appropriate starting materials.

Another advantage of the process is that polymerization stabilizes the state: Once the molecules have aligned, they cannot simply move freely again and are held in place. As a result, the electrical potential is maintained under ambient conditions. At higher temperatures, such as 90 degrees Celsius, the coating loses its polarization again.

New Functions for Thin Polymer Coatings

The new method opens up a wide range of possibilities for future applications. For example, the self-polarizing polymer films could be used in electronics, sensor technology, energy technology, or at biological interfaces. 

A particular advantage of the process is that it can uniformly coat even complex-shaped surfaces. This could make it possible in the future to generate electrical fields in a targeted manner on three-dimensional surfaces. The team believes that, in the long term, these coatings could help reduce the energy consumption of electronic components.

“For industrial applications, it is very interesting that the polymer films do not need to be externally polarized and that surface potentials can be precisely adjusted,” says materials scientist Dr. Torge Hartig, who is also an author of the study and co-founded the company Conformally with Schröder and other colleagues from the CAU. “Furthermore, previous polarized polymer films typically contain PFAS. With this new effect, more sustainable, PFAS-free polarized polymer films are now possible.”

With Conformally, Hartig and his team are bringing iCVD technology from the research lab into industrial applications. The process makes it possible to apply exceptionally thin and uniform coatings even to complex-shaped surfaces. These self-polarizing polymer films would be in demand wherever electric fields are needed directly on surfaces: for example, in sensors, detectors, or microelectronic components, such as those found in cell phones. The authors also consider applications in solar cells to be a possibility.