Researchers from Penn State used the approach of Morphotropic Phase Boundary (MPB) to enhance piezoelectric properties in organic polymers
The inability to alter intrinsic piezoelectric behavior in organic polymers restrains the application of these polymers in flexible, wearable, and biocompatible devices. Now, a team of researchers at Penn State and North Carolina State University, suggested that a molecular approach can improve those piezoelectric properties in organic polymers. The concept of Morphotropic Phase Boundary (MPB) was developed in ceramic materials. However, the concept was not identified in organic materials. MPB refers to significant changes in material properties that occur at the boundary between crystalline structures. Moreover, it is dependent on a material’s composition. The piezoelectric effect is a reversible process that occurs in some materials. Physical compression of a material leads to generation of an electrical charge and the flow of an electric current results in mechanical motion.
The team observed ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) — P(VDF-TrFE) — copolymers and found that these molecules can be altered to specific arrangements around chiral, or asymmetric. This causes transitions between ordered and disordered structures at the centers and creates a region within the material where ferroelectric and relaxor properties compete. Relaxors are disorganized materials, whereas normal ferroelectric materials are uniform and ordered. An MPB-like effect in ferroelectric polymers is induced by the molecular chain conformations that are tailored by chemical compositions. The team used a combined experiment and theory approach to study MPB formation in organic materials.
The approach included first principles calculations of possible configurations and synthesis of new polymers and comprehensive characterization of structures and properties. The approach was simulated at North Carolina State University and the team also used a wide variety of methods to investigate the polymer such as nuclear magnetic resonance, x-ray powder diffraction, and Fourier-transformed infrared spectroscopy that observed the transition area and boundaries. According to the researchers, the flexibility in molecular design and synthesis found in the research facilitates a new avenue for scalable high-performance piezoelectric polymers. The research was published in the journal Nature on October 04, 2018.