Breakthrough in Synthesis of Elastic Ferroelectric Materials by HLS Users

Wearable electronics with stretchability should possess sufficient elasticity to conform to biological tissues and adapt to body movements involving large and frequent strains. These requirements have gradually become fundamental characteristics for materials used in skin-like elastic electronic devices. Recently, prototypes of wearable sensors and circuits based on intrinsically elastic conductors or semiconductors have been proposed. However, the elastic ferroelectrics produced by ferroelectrics' elasticity, as the key and promising basic materials of modern electronics, still lag behind their intrinsic elastic counterparts, hindering their application in emerging wearable devices. Over the past few years, chemical cross-linking has made significant strides in achieving intrinsic elasticity in semiconductors and conductors. However, from the perspective of elastifying polymer ferroelectrics, traditional chemical cross-linking can still lead to a ferroelectric response-elastic recovery dilemma. More specifically, the ferroelectricity of PVDF-based polymer ferroelectrics originates from the orientation and polarization of ferroelectric (FE) domains within crystalline regions, meaning that excellent FE response requires high crystallinity. Therefore, resolving the FE response-elastic recovery conundrum during FE elastification to achieve both excellent elasticity and high crystallinity is challenging. Recently, researcher Benlin Hu at the Ningbo Institute of Materials Technology and Engineering developed an intrinsically elastic ferroelectric by incorporating both ferroelectric response and elastic rebound into a single material through slight cross-linking of the ferroelectric polymer. Precise micro-cross-linking enables a sophisticated balance between crystallinity and resilience. An elastic ferroelectric was obtained, demonstrating stable ferroelectric response under mechanical deformation of up to 70% strain. This elastic ferroelectric holds potential for applications related to wearable electronics, such as elastic ferroelectric sensors, information storage, and energy transduction.

Figure A. Schematic diagrams illustrating the macroscopic and molecular-scale changes of a polymer ferroelectric under strain and elastic deformation. Figure B. N K-edge NEXAFS spectra of the cross-linker PEG-diamine and P(VDF-TrFE) with different cross-linking densities.

Utilizing the Photoemission End-Station (BL10B) at the Hefei Light Source, the team investigated the soft X-ray absorption spectra of pristine P(VDF-TrFE), P(VDF-TrFE) blended with the cross-linker, the cross-linker PEG-diamine itself, and the cross-linked P(VDF-TrFE). NEXAFS spectra of the F and C elements revealed that the chemical states of F and C remained almost unchanged at low cross-linking density. NEXAFS spectra of the N element showed that the amino peak from the cross-linker (PEG-diamine) disappeared after cross-linking, and an imine peak appeared in the material. These results successfully demonstrated the slight cross-linking between P(VDF-TrFE) and PEG-diamine via imine bonds. Subsequent characterization proved that, compared to other cross-linking methods, using diamine as the cross-linker offered higher reactivity. Low cross-linking intensity could impart elastic resilience (recoverable up to 125% strain) to the linear polymer while maintaining high crystallinity, thereby achieving a good ferroelectric (FE) response. This research outcome provides new insights for the development of wearable electronics. The related findings were published in the renowned international academic journal Science under the title Intrinsically elastic polymer ferroelectric by precise slight cross-linking.

Paper link：https://www.science.org/doi/10.1126/science.adh2509