Breakthrough in Soft Robotics: Ferroelectric Polymer Unleashes Artificial Muscles

Penn State researchers have achieved a significant breakthrough by developing a highly efficient ferroelectric polymer capable of converting electrical energy into mechanical strain. This innovative material overcomes the limitations of traditional piezoelectric polymers and holds immense promise for applications in medical devices, robotics, and precision positioning systems. By creating a polymer nanocomposite, the researchers have drastically reduced the required driving field strength, thus expanding the potential applications of this technology.

The groundbreaking ferroelectric polymer demonstrates exceptional capabilities in converting electrical energy into mechanical strain, making it an ideal candidate for high-performance motion control or “actuation.” This development opens up exciting possibilities for medical devices, advanced robotics, and precision positioning systems. Unlike rigid actuator materials of the past, soft actuators such as ferroelectric polymers offer greater flexibility and adaptability to various environmental conditions.

The research showcased the potential of ferroelectric polymer nanocomposites in overcoming the limitations of conventional piezoelectric polymer composites. This breakthrough provides a promising path for developing soft actuators with enhanced strain performance and mechanical energy density. Robotics researchers, in particular, are intrigued by the strength, power, and flexibility of soft actuators, as they can revolutionize the field.

Qing Wang, a professor of materials science and engineering at Penn State and co-corresponding author of the study published in the journal Nature Materials, envisions the possibility of creating “artificial muscles” using this new soft robotics technology. Wang explains that this advancement would yield a material that closely mimics human muscle, possessing both high load-carrying capacity and a large strain.

However, before these materials can fulfill their potential, a few challenges must be addressed. The study proposes potential solutions to these obstacles. Ferroelectrics are materials that exhibit spontaneous electric polarization when subjected to an external electric charge, causing positive and negative charges to accumulate at different poles. The phase transition in these materials, such as the conversion of electrical energy to mechanical energy, can lead to a significant change in their properties, making them suitable for use as actuators.

A commonly encountered application of ferroelectric actuators is in inkjet printers, where changes in electrical charge alter the actuator’s shape, enabling precise control of the tiny nozzles that deposit ink on paper.

While many ferroelectric materials are ceramics, they can also exist as polymers—a category of natural and synthetic materials composed of similar units bonded together. Ferroelectric polymers offer a remarkable ability to generate the electric-field-induced strain required for actuation. Their strain capabilities exceed those of other ferroelectric materials like ceramics.

This desirable property, combined with their high flexibility, reduced cost compared to other ferroelectric materials, and lightweight nature, has captured the interest of researchers in the burgeoning field of soft robotics, where robots with flexible components and electronics are designed.

Wang explains that the study proposes solutions to two major challenges in the field of soft material actuation. The first challenge is improving the force generated by soft materials. While soft actuation materials like polymers exhibit significant strain, they generally produce less force compared to piezoelectric ceramics.

The second challenge is that ferroelectric polymer actuators typically require a very high driving field—a force that induces a change in the system—to generate the necessary shape change for ferroelectric reactions and actuation. To enhance the performance of ferroelectric polymers, the researchers developed a percolative ferroelectric polymer nanocomposite. By incorporating nanoparticles into a polymer called polyvinylidene fluoride, they created an interconnected network of poles within the polymer structure.

This network facilitated the induction of a ferroelectric phase transition at significantly lower electric fields than conventionally required. The researchers achieved this using an electro-thermal method called Joule heating, which generates heat when an electric current passes through a conductor. By leveraging Joule heating to induce the phase transition in the nanocomposite polymer, they reduced the necessary electric field strength to less than 10% of what is typically needed for ferroelectric phase change.

Wang elaborates that this breakthrough allows for the integration of strain and force into a single material, with the new approach utilizing the advantages of Joule heating. The resulting lower driving field requirement opens up a wide range of applications, including medical devices, optical devices, and soft robotics, where a low driving field is crucial for optimal functionality.

The study, titled “Electro-thermal actuation in percolative ferroelectric polymer nanocomposites,” was authored by a team of researchers including Yang Liu, Yao Zhou, Hancheng Qin, Tiannan Yang, Xin Chen, Li Li, Zhubing Han, Ke Wang, Bing Zhang, Wenchang Lu, Long-Qing Chen, J. Bernholc, and Qing Wang. The research received partial support from the United States Department of Energy.

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More about ferroelectric polymer

• Penn State News – Artificial Muscles Flex for the First Time: Ferroelectric Polymer Innovation in Robotics
• Nature Materials – Electro-thermal actuation in percolative ferroelectric polymer nanocomposites
• ScienceDaily – Artificial Muscles Flex for the First Time: Ferroelectric Polymer Innovation in Robotics