BREAKING! SEUer’s research achievements published in Science!

Dr. Zhang Hanyue, a young faculty member from the School of Biological Science and Medical Engineering, SEU, in collaboration with Prof. Xiong Ren’gen, published a perspective paper entitled “Ferroelectric polymers take a step toward bioelectronics” in Science (Science 2023, 381, 540-544). This publication is supported by the National Natural Science Foundation of China, the Start-up Cultivation Fund of “SEU Top 10 Scientific and Technological Issues”, and the independent programs of Jiangsu Key Laboratory for Biomaterials and Devices. Guided by Prof. Xiong Ren’gen, a pioneer in ferroelectric chemistry, the authors reviewed and discussed the intrinsic elasticity achieved in P(VDF-TrFE)-based flexible ferroelectric polymers in combination with recent progress gained in the field of ferroelectric chemistry. Zhang Hanyue is both the first author and corresponding author of the paper, with SEU listed as the first corresponding institute.

Ferroelectric material, as an important functional material, holds significant implications across various sectors, including national defense, aerospace, information technology, energy, and healthcare, among others. With the progress of this era, there have been greater demands and higher expectations for electronic devices. To fulfill the evolving requisites of bioelectronics applications such as soft robots, health monitoring devices, and wearable electronics, ferroelectric materials are supposed to be soft and flexible, possessing excellent elasticity. These requirements have posed substantial challenges for conventional ferroelectric materials which inherently tend to be rigid and brittle, such as inorganic oxides and ion crystals. Despite their favorable mechanical flexibility, ferroelectric polymers, exemplified by polyvinylidene fluoride (PVDF) and its copolymers, often exhibit irreversible plastic deformation.

This paper introduces rubber, one of the most common elastic materials in our daily life, which is generally an amorphous polymer featuring lower glass-transition temperature. To realize effective elastic recovery, polymer materials should feature lower crystallinity. However, ferroelectricity is commonly observed in crystalline compounds, where long-range ordered polar structures are crucial for ferroelectricity. From this aspect, chemical cross-linking is a common and straightforward method to achieve intrinsic elasticity. However, traditional chemical cross-linking may significantly reduce the crystallinity of the polymer, leading to a weakened ferroelectric response. Therefore, the challenge of achieving both excellent ferroelectricity and high resilience in a single material has been considered as a significant hurdle in the development of ferroelectric materials for over a century.

The paper further elaborated on the research published in the same issue of Science, which concentrated on achieving the intrinsic elasticity in P(VDF-TrFE)-based ferroelectric polymer through chemical modification. Gao et al. proposed a chemical cross-linking method with an exceedingly low cross-linking density (1-2%) to achieve the elasticity in the plastic P(VDF-TrFE)-based polymers (as depicted in the figure below). Their investigation revealed that the copolymer of P(VDF-TrFE) with a VDF molar fraction of 55% exhibited the lowest modulus and the highest elongation at break. Consequently, they chemically modified the P(VDF-TrFE)-based plastic polymer with this specific composition. By using a soft long-chain cross-linking agent, polyethylene glycol (PEG) diamine, they partially cross-linked the P(VDF-TrFE)-based plastic polymer chains (the optimal cross-linking density of 1.44%), thus forming an elastic cross-linked network. Such modification has endowed the P(VDF-TrFE)-based polymer with ideal resilience while retaining high crystallinity for sound ferroelectric performance. The resulting elastic ferroelectric polymer exhibited excellent elastic strain recovery, up to 125%. It is particularly noteworthy that, the chemically modified elastic ferroelectric polymer, even under 70% strain, still displayed a clear ferroelectric hysteresis loop, indicating that it still maintained sound ferroelectric bi-stability under stress and tension.

The conclusion of the paper highlighted the promising prospect of incorporating the single chiral strategy into ferroelectric chemical design, which opens up a wealth of possibilities for the future development of elastic ferroelectric materials. The introduction of single chirality is one of important principles within ferroelectric chemical theory, as proposed by Prof. Xiong Ren’gen, for the design of molecular ferroelectrics. Introducing the chiral monomers into polymers or using chiral cross-linking agents to modify polymers can transmit the asymmetry caused by single chirality to the molecular structure layer by layer. This is vital for the construction of electrically active ferroelectric polymers. At the same time, the chirality will also endow ferroelectric polymers with new functional properties, such as chiroptical properties and catalytic enantioselectivity etc. Taking into account the recent advancements in the field of ferroelectric chemistry, this perspective paper also envisions the profound potential of elastic ferroelectric materials in biomedical applications. In the future, elastic ferroelectric materials will emerge as an important research trajectory in the field of ferroelectricity.

Dr. Zhang Hanyue is currently working at Jiangsu Key Laboratory of Biomedical Materials and Devices, SEU. Her research focuses on the chemical design of molecular ferroelectric materials and their biomedical applications, with a particular emphasis on organic silicon-based ferroelectric materials. She aims to conduct interdisciplinary research in ferroelectric chemistry and biomedical applications to address biomedical challenges. Since starting her independent work, Dr. Zhang has published her research findings in prestigious international journals, including Science, Physical Review Letters, Journal of the American Chemical Society, Angewandte Chemie International Editionetc.