Fluorine-Free Polymer Redefines Wearable Tech

The device worn on your wrist may measure your heart rate, track your sleep, or count your steps, but it likely contains fluorine, a harmful forever chemical. However, researchers at Case Western Reserve University’s (CWRU) School of Engineering have developed a fluorine-free plastic option: ferroelectric polymer.   

This new option has the potential to revolutionize wearable electronics, sensors, and other electrical technologies while also protecting the environment, according to the research team.
 

Designing a new generation of polymers

Lei Zhu, a professor of Macromolecular Science and Engineering at CWRU, has spent the past decade advancing polymer research, from high-dielectric materials for energy storage to semicrystalline and liquid-crystalline sulfonated polymers, and most recently, ferroelectric polymers. His work explores next-generation plastics and polymeric systems designed to tackle global challenges in energy, sustainability, electronics, health, and the environment. 

Polymers are large molecules made of repeating units. They can be synthetic, like plastic, or they can come from nature. By adjusting their molecular makeup, it’s possible to realize and fine-tune their ferroelectricity—a long-awaited breakthrough to a “perplexing problem” during the last three years of the team’s study, recently published in Science.

“In the past, ferroelectric polymers were mostly discovered. They were not made by design,” Zhu said. “The way these new polymers produce their ferroelectric properties is fundamentally different [from the discovered polymers]. Unlike existing ferroelectric materials, they don’t need to crystalize to lock in the polarity that enables the ferroelectrical behavior.”

Jiahao Huang, who is working on post-doctoral research in dielectric polymers said, “The original idea was proposed in discussions between me and Professor Zhu.”

Huang also took a leading role in the synthesis and molecular design of the various deployments of ferroelectric polymers.  

Describing the design process, Huang explained that “the key is molecular design. What kind of molecular unit do you need in polymer to introduce ferroelectricity? So, I introduced two very polar molecular groups in the polymers to achieve ferroelectricity in the polymers.”  

Huang continued: “You need to start with very simple chemicals—by doing several steps of organic synthesis to finally get this polymer. I did about ten steps of organic synthesis, including substitution and chain elongation, to achieve ferroelectricity in the polymers.”

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There was a moment of suspense for the researchers as they did their final dielectric measurements and waited to see if their hypothesis would be confirmed.  

“I didn’t know what would happen before that,” Huang said. “But after we confirmed that it’s a new deployment we felt surprised and very happy.”  

“We worked together,” Zhu added. “We discussed it day and night. But Professor Zhu made it. He realized it. It was hard work. And then, all of a sudden, it happened.”  
 

Unlocking new properties

The organic synthesis process, Zhu noted, required no special equipment except a standard flask, which they scaled up in 10-gram scales. From there, they were able to examine a wide range of self-assembled structures and their electroactive behaviors by creating polymers with varying molecular arrangements.

Adjusting the position of the methyl group within the polymer chain significantly altered its properties, resulting in a diverse set of ferroelectric characteristics. The work has since expanded to include piezoelectric materials, representing a major step forward in polymer science. 

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While Zhu does not foresee the immediate commercialization or scaling up of the ferroelectric polymer, this work has opened a “gold mine” of knowledge that will open the door to more scientific knowledge, he said.  

“If you open a new area then there are many things to do,” Zhu said. “You don’t just dig this thing out then throw it away. You dig and there’s a gold mine beneath where you need to go deeper and do more.”  

The new polymer is both flexible and has tunable electronic properties, which means it can switch on and off. It’s well suited to applications such as infrared sensors and wearable devices that require materials that are soft, stretchable, and compatible with the human body.  
 

Toward smarter, sustainable electronics

Other areas where it shows promise are in ultrasound diagnostic tools, where compatibility with biological tissues is crucial and in augmented or virtual reality technologies.  

Huang also believes it will also be useful in energy harnessing and solid-state cooling.  

“You wouldn’t need a refrigerant for cooling in an air conditioner,” he said. “You could use polymers to cool a room or your cell phone.”  

The team has filed a provisional patent and is in discussions with several companies regarding areas such as wearable electronics. These piezoelectric and electric polymer materials are of interest in the technology, Zhu added.  

There are many promising uses, but there is still work to be done.  

“We are still synthesizing small batches and learning more about the properties. But we’re very optimistic about replacing environmentally harmful plastics in future flexible electronics,” Zhu said. 

Annemarie Mannion is a technology writer in Chicago.