A molecular model of the ferroelectric copolymer poly(vinylidene fluoride-co-trifluoroethylene). Image: Modified from Kamal Asadi.
A molecular model of the ferroelectric copolymer poly(vinylidene fluoride-co-trifluoroethylene). Image: Modified from Kamal Asadi.

The inability to alter intrinsic piezoelectric behavior in organic polymers hampers their application in flexible, wearable and biocompatible devices, say researchers at Penn State and North Carolina State University. Now, these researchers have come up with a molecular approach, based on a concept known as a morphotropic phase boundary, for improving the piezoelectric properties of organic polymers.

"Morphotropic phase boundary (MPB) is an important concept developed a half-century ago in ceramic materials," explained Qing Wang, professor of materials science and engineering at Penn State. "This concept has never before been realized in organic materials."

The concept of morphotropic phase boundary relates to significant changes in material properties that occur at the boundary between crystalline structures, and which are dependent on a material's composition.

The piezoelectric effect is a reversible process that occurs in some materials. Physically compressing these materials produces an electric charge, while passing an electric current through the materials produces mechanical motion.

The researchers were investigating ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) P(VDF-TrFE) copolymers. They found that tailoring the molecules making up the copolymers so that they adopted specific arrangements around chiral, or asymmetric, centers led to transitions between ordered and disordered structures, and created a region within the material where ferroelectric and relaxor properties compete. Relaxors are disorganized materials, while normal ferroelectric materials are ordered. This caused an MPB-like effect to be induced between the different regions.

"We studied MPB formation in organic materials using a combined experiment and theory approach – first principles calculations of possible configurations, synthesis of new polymers and comprehensive characterization of structures and properties," said Wang. The simulation work was done at North Carolina State University.

The researchers also used a wide variety of analytical methods to investigate the ferroelectric polymer including nuclear magnetic resonance, x-ray powder diffraction and Fourier-transformed infrared spectroscopy. These methods allowed them to study the transition area and boundaries.

"Given flexibility in molecular design and synthesis, this work opens up a new avenue for scalable high-performance piezoelectric polymers," the researchers report in a paper on this work in Nature.

This story is adapted from material from Penn State, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.