@article{liu_zhou_qin_yang_chen_li_han_wang_zhang_lu_et al._2023, title={Electro-thermal actuation in percolative ferroelectric polymer nanocomposites}, volume={5}, ISSN={["1476-4660"]}, DOI={10.1038/s41563-023-01564-7}, abstractNote={The interconversion between electrical and mechanical energies is pivotal to ferroelectrics to enable their applications in transducers, actuators and sensors. Ferroelectric polymers exhibit a giant electric-field-induced strain (>4.0%), markedly exceeding the actuation strain (≤1.7%) of piezoelectric ceramics and crystals. However, their normalized elastic energy densities remain orders of magnitude smaller than those of piezoelectric ceramics and crystals, severely limiting their practical applications in soft actuators. Here we report the use of electro-thermally induced ferroelectric phase transition in percolative ferroelectric polymer nanocomposites to achieve high strain performance in electric-field-driven actuation materials. We demonstrate a strain of over 8% and an output mechanical energy density of 11.3 J cm -3  at an electric field of 40 MV m -1  in the composite, outperforming the benchmark relaxor single-crystal ferroelectrics. This approach overcomes the trade-off between mechanical modulus and electro-strains in conventional piezoelectric polymer composites and opens up an avenue for high-performance ferroelectric actuators.}, journal={NATURE MATERIALS}, author={Liu, Yang and Zhou, Yao and Qin, Hancheng and Yang, Tiannan and Chen, Xin and Li, Li and Han, Zhubing and Wang, Ke and Zhang, Bing and Lu, Wenchang and et al.}, year={2023}, month={May} }
 @article{chen_qin_liu_lin_zhang_lu_kim_bernholc_wang_zhang_2023, title={Interfacial origin of dielectric constant enhancement in high-temperature polymer dilute nanocomposites}, volume={122}, ISSN={["1077-3118"]}, url={https://doi.org/10.1063/5.0143938}, DOI={10.1063/5.0143938}, abstractNote={The origin of dielectric constant enhancement in high-temperature (high glass transition temperature Tg) polymer dilute nanocomposites is investigated via Infrared (IR) Spectroscopy applied through Atomic Force Microscope (AFM) and density functional theory (DFT) calculations. The dielectric constant can be greatly enhanced by trace nanofiller loadings (<0.5 vol. %) in a broad class of high-temperature polymers without affecting or even with a positive influence on breakdown strength and dielectric loss. This avenue provides attractive polymer systems for high-performance polymer-based capacitive energy storage in a wide temperature range. In the dilute nanocomposites, the interface regions between the polymers and trace nanofillers are the key to the observed dielectric constant enhancement. This Letter employs AFM-IR to study chain packing in the interface regions of polyetherimide (PEI) dilute nanocomposites. The experimental results and DFT calculations indicate that flexible linkages, i.e., ether groups in PEI, play a crucial role in inducing heterogeneous morphologies in the interface regions. These results are confirmed by studies of PI(PDMA/ODA) and other dilute polymer nanocomposites in the literature as well as by lack of dielectric constant enhancement in PI(Matrimid® 5218) that does not contain flexible linkages.}, number={21}, journal={APPLIED PHYSICS LETTERS}, author={Chen, Xin and Qin, Hancheng and Liu, Yang and Lin, Yen-Ting and Zhang, Bing and Lu, Wenchang and Kim, Seong H. H. and Bernholc, J. and Wang, Qing and Zhang, Q. M.}, year={2023}, month={May} }
 @article{zhou_xu_zhang_zhang_shen_xu_liu_bertram_bernholc_jiang_et al._2022, title={Curly-Packed Structure Polymers for High-Temperature Capacitive Energy Storage}, volume={34}, ISSN={["1520-5002"]}, url={https://doi.org/10.1021/acs.chemmater.1c04220}, DOI={10.1021/acs.chemmater.1c04220}, abstractNote={Polymer film capacitors are ubiquitous in modern electronics and electric systems, but the relatively low working temperatures of polymer dielectrics limit their application in next-generation capacitors. The currently reported high-temperature polymer dielectrics rely on the construction of nanocomposites with wide band gap fillers and cross-linked networks to achieve high breakdown strength and high efficiencies. However, generating the optimal chain structure with intrinsic great high-temperature capacitive properties using a one-component polymer is still challenging. Herein, a giant discharged energy density in neat polymer has been demonstrated in a series of linear poly(arylene ether amide) (PNFA) at 150 °C, which greatly surpass all the current free-standing dielectric polymer films measured in 10 Hz. The maximum discharged energy density with efficiency above 90% of the PNFA is 2.7 J cm–3, which is about 3 times that of the state-of-the-art commercial high-temperature polymer films. The architectures of the amorphous polymers have been identified by synchrotron X-ray diffraction combined with density functional theory calculations. The origins of superior high-temperature capacitive properties are traced to the increased packing density by the curly-packed chain structure. In addition, the reported polymer could be produced using existing industrial-grade processes, which are economical and practical for large-scale applications.}, number={5}, journal={CHEMISTRY OF MATERIALS}, publisher={American Chemical Society (ACS)}, author={Zhou, Chenyi and Xu, Wenhan and Zhang, Bing and Zhang, Yunhe and Shen, Chen and Xu, Qinfei and Liu, Xin and Bertram, Florian and Bernholc, Jerzy and Jiang, Zhenhua and et al.}, year={2022}, month={Mar}, pages={2333–2341} }
 @article{chen_qin_qian_zhu_li_zhang_lu_li_zhang_zhu_et al._2022, title={Relaxor ferroelectric polymer exhibits ultrahigh electromechanical coupling at low electric field}, volume={375}, ISSN={["1095-9203"]}, DOI={10.1126/science.abn0936}, abstractNote={
            Electromechanical (EM) coupling—the conversion of energy between electric and mechanical forms—in ferroelectrics has been used for a broad range of applications. Ferroelectric polymers have weak EM coupling that severely limits their usefulness for applications. We introduced a small amount of fluorinated alkyne (FA) monomers (<2 mol %) in relaxor ferroelectric poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (PVDF-TrFE-CFE) terpolymer that markedly enhances the polarization change with strong EM coupling while suppressing other polarization changes that do not contribute to it. Under a low–dc bias field of 40 megavolts per meter, the relaxor tetrapolymer has an EM coupling factor (
            k
            33
            ) of 88% and a piezoelectric coefficient (
            d
            33
            ) >1000 picometers per volt. These values make this solution-processed polymer competitive with ceramic oxide piezoelectrics, with the potential for use in distinct applications.
          }, number={6587}, journal={SCIENCE}, author={Chen, Xin and Qin, Hancheng and Qian, Xiaoshi and Zhu, Wenyi and Li, Bo and Zhang, Bing and Lu, Wenchang and Li, Ruipeng and Zhang, Shihai and Zhu, Lei and et al.}, year={2022}, month={Mar}, pages={1418-+} }
 @article{zhang_chen_zhang_zhang_lu_chen_liu_kim_donovan_warzoha_et al._2021, title={High-temperature polymers with record-high breakdown strength enabled by rationally designed chain-packing behavior in blends}, volume={4}, ISSN={["2590-2385"]}, DOI={10.1016/j.matt.2021.04.026}, abstractNote={Polymers with high dielectric breakdown strength (Eb) over a broad temperature range are vital for many applications. The presence of weak points, such as voids and free volume, severely limit the Eb of many high-temperature polymers. Here, we present a general strategy to reduce these weak points by exploiting interchain electrostatic forces in polymer blends. We show that the strong interchain electrostatic interaction between two high-temperature polymers in blends of polyimide (PI) with poly(ether imide) (PEI) yields an extended polymer chain conformation, resulting in dense chain packing and a corresponding decrease in weak spots in the polymers. This leads to a greater than 65% enhancement of Eb at room temperature and 35% enhancement at 200°C. In conjunction with results from blends of PI/poly(1,4-phenylene ether-sulfone) (PSU) and blends of PEI/PSU, we show that this previously unexplored molecular engineering strategy is efficient and straightforward in minimizing weak points in dielectric polymers.}, number={7}, journal={MATTER}, author={Zhang, Qiyan and Chen, Xin and Zhang, Bing and Zhang, Tian and Lu, Wengchang and Chen, Zhe and Liu, Ziyu and Kim, Seong H. and Donovan, Brian and Warzoha, Ronald J. and et al.}, year={2021}, month={Jul}, pages={2448–2459} }
 @article{zhang_chen_lu_zhang_bernholc_2021, title={Morphology-induced dielectric enhancement in polymer nanocomposites}, volume={13}, ISSN={["2040-3372"]}, url={https://doi.org/10.1039/D1NR00165E}, DOI={10.1039/d1nr00165e}, abstractNote={Admixture of dilute nanoparticles into dipolar polymer dielectrics enlarges free volume and increases permittivity by over 50%.}, number={24}, journal={NANOSCALE}, publisher={Royal Society of Chemistry (RSC)}, author={Zhang, Bing and Chen, Xin and Lu, Wenchang and Zhang, Q. M. and Bernholc, J.}, year={2021}, month={Jun} }
 @article{liu_yang_zhang_williams_lin_li_zhou_lu_kim_chen_et al._2020, title={Structural Insight in the Interfacial Effect in Ferroelectric Polymer Nanocomposites}, volume={32}, ISSN={["1521-4095"]}, DOI={10.1002/adma.202005431}, abstractNote={Abstract}, number={49}, journal={ADVANCED MATERIALS}, author={Liu, Yang and Yang, Tiannan and Zhang, Bing and Williams, Teague and Lin, Yen-Ting and Li, Li and Zhou, Yao and Lu, Wenchang and Kim, Seong H. and Chen, Long-Qing and et al.}, year={2020}, month={Dec} }
 @article{liu_zhang_haibibu_xu_han_lu_bernholc_wang_2019, title={Insights into the Morphotropic Phase Boundary in Ferroelectric Polymers from the Molecular Perspective}, volume={123}, ISSN={1932-7447 1932-7455}, url={http://dx.doi.org/10.1021/acs.jpcc.9b01220}, DOI={10.1021/acs.jpcc.9b01220}, abstractNote={Significantly enhanced electromechanical responses are inherent to piezoelectric materials at the morphotropic phase boundary (MPB). Here we reveal that conformational competition between the trans-planar and 3/1-helical phases of poly(vinylidene fluoride–trifluoroethylene) P(VDF-TrFE) occurs intramolecularly rather than intermolecularly to induce the formation of MPB. We attribute significantly enhanced piezoelectric properties observed near MPB to the polarization rotation between energetically degenerate trans-planar and 3/1-helical phases. Our results offer design principles to search for new MPB polymers from a molecular perspective.}, number={14}, journal={The Journal of Physical Chemistry C}, publisher={American Chemical Society (ACS)}, author={Liu, Yang and Zhang, Bing and Haibibu, Aziguli and Xu, Wenhan and Han, Zhubing and Lu, Wenchang and Bernholc, J. and Wang, Qing}, year={2019}, month={Mar}, pages={8727–8730} }
 @article{liu_aziguli_zhang_xu_lu_bernholc_wang_2018, title={Ferroelectric polymers exhibiting behaviour reminiscent of a morphotropic phase boundary}, volume={562}, ISSN={0028-0836 1476-4687}, url={http://dx.doi.org/10.1038/s41586-018-0550-z}, DOI={10.1038/s41586-018-0550-z}, abstractNote={Piezoelectricity-the direct interconversion between mechanical and electrical energies-is usually remarkably enhanced at the morphotropic phase boundary of ferroelectric materials 1-4 , which marks a transition region in the phase diagram of piezoelectric materials and bridges two competing phases with distinct symmetries 1,5 . Such enhancement has enabled the recent development of various lead and lead-free piezoelectric perovskites with outstanding piezoelectric properties for use in actuators, transducers, sensors and energy-harvesting applications 5-8 . However, the morphotropic phase boundary has never been observed in organic materials, and the absence of effective approaches to improving the intrinsic piezoelectric responses of polymers 9,10  considerably hampers their application to flexible, wearable and biocompatible devices. Here we report stereochemically induced behaviour in ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) copolymers, which is similar to that observed at morphotropic phase boundaries in perovskites. We reveal that compositionally tailored tacticity (the stereochemical arrangement of chiral centres related to the TrFE monomers 11,12 ) can lead to intramolecular order-to-disorder evolution in the crystalline phase and thus to an intermediate transition region that is reminiscent of the morphotropic phase boundary, where competing ferroelectric and relaxor properties appear simultaneously. Our first-principles calculations confirm the crucial role of chain tacticity in driving the formation of this transition region via structural competition between the trans-planar and 3/1-helical phases. We show that the P(VDF-TrFE) copolymer with the morphotropic composition exhibits a longitudinal piezoelectric coefficient of -63.5 picocoulombs per newton, outperforming state-of-the-art piezoelectric polymers 10 . Given the flexibility in the molecular design and synthesis of organic ferroelectric materials, this work opens up the way for the development of scalable, high-performance piezoelectric polymers.}, number={7725}, journal={Nature}, publisher={Springer Nature}, author={Liu, Yang and Aziguli, Haibibu and Zhang, Bing and Xu, Wenhan and Lu, Wenchang and Bernholc, J. and Wang, Qing}, year={2018}, month={Oct}, pages={96–100} }
 @article{thakur_zhang_dong_lu_iacob_runt_bernholc_zhang_2017, title={Generating high dielectric constant blends from lower dielectric constant dipolar polymers using nanostructure engineering}, volume={32}, ISSN={2211-2855}, url={http://dx.doi.org/10.1016/j.nanoen.2016.12.021}, DOI={10.1016/j.nanoen.2016.12.021}, abstractNote={It is a great challenge in dielectric polymers to achieve a high dielectric constant while maintaining low dielectric loss and high operating temperatures. Here we report that by blending two glassy state dipolar polymers i.e., poly(arylene ether urea) (PEEU, K=4.7) and an aromatic polythiourea (ArPTU, K=4.4) to form a nanomixture, the resulting blend exhibits a very high dielectric constant, K=7.5, while maintaining low dielectric loss (<1%). The experimental and computer simulation results demonstrate that blending these dissimilar dipolar polymers causes a slight increase in the interchain spacing of the blend in its glassy state, thus reducing the barriers for reorientation of dipoles in the polymer chains along the applied electric field and generating a much higher dielectric response than the neat polymers.}, journal={Nano Energy}, publisher={Elsevier BV}, author={Thakur, Yash and Zhang, Bing and Dong, Rui and Lu, Wenchang and Iacob, C. and Runt, J. and Bernholc, J. and Zhang, Q.M.}, year={2017}, month={Feb}, pages={73–79} }