Researchers at Pennsylvania State University said they developed a new ferroelectric polymer that could convert electrical energy into mechanical strain.

Such a polymer could offer potential for applications in medical devices, advanced robotics and precision positioning systems. The team says that mechanical strain represents an important property for an actuator. Traditionally, these actuator materials were rigid, but soft ones like the ferroelectric polymers offer more flexibility and environmental adaptability.

According to a post on the PSU website, the research showcased the potential for these polymers to overcome the limitations of traditional piezoelectric polymer composites. This could enable soft actuators with enhanced strain performance and mechanical energy density.

“Potentially we can now have a type of soft robotics that we refer to as artificial muscle,” said Qing Wang, Penn State professor of materials science and engineering and co-corresponding author of the study recently published in Nature Materials. “This would enable us to have soft matter that can carry a high load in addition to a large strain. So that material would then be more of a mimic of human muscle, one that is close to human muscle.”

What makes this polymer work

The researchers say that the materials used in this research demonstrate a spontaneous electric polarization with an external electric charge. Positive and negative charges in the materials head to different poles. Strain in these materials during this phase transition can completely change properties like shape. This makes the polymers useful as actuators.

One common use comes in inkjet printers. Electrical charge takes the shape of the actuator to control the nozzles that deposit ink on paper.

The researchers say the polymer exhibits a tremendous amount of electric-field-induced strain needed for actuation. Combined with high levels of flexibility, low weight and reduced cost, they offer a high-potential option in soft robotics.

“In this study we proposed solutions to two major challenges in the soft material actuation field,” said Wang. “One is how to improve the force of soft materials. We know soft actuation materials that are polymers have the largest strain, but they generate much less force compared to piezoelectric ceramics.”

How the team integrated it

The team believed the solution to improving the ferroelectric polymer performance came in the form of a nanocomposite. By incorporating nanoparticles into a type of polymer — polyvinylidene fluoride — the researchers created an interconnected network of poles within the polymer. This network enabled a ferroelectric phase transition inducement at much lower electric fields compared to normal requirements.

Using an electro-thermal method using Joule heating, the team induced the phase transition in the nanocomposite polymer. It only required less than 10% of the strength of an electric field typically needed for ferroelectric phase change.

“Typically, this strain and force in ferroelectric materials are correlated with each other, in an inverse relationship,” Wang said. “Now we can integrate them together into one material, and we developed a new approach to drive it using the Joule heating. Since the driving field is going to be much lower, less than 10%, this is why this new material can be used for many applications that require a low driving field to be effective, such as medical devices, optical devices and soft robotics.”