Flexible reversible drives have great application potential in flexible electronics, soft robots and other fields. Hybrid ion/electronic conductor flexible thin-film drives have gained a lot of attention in recent years. However, since the conduction of ions and electrons depends on mutually exclusive conduction mechanisms, achieving high ionic/electronic conductivity coupling in flexible films or hydrogels with high mechanical strength is a great challenge in the field.
Recently, the team of Professor Lars A. Berglund of the Royal Institute of Technology (KTH) of Sweden, together with Associate Professor KTH Mahiar M. Hamedi, Associate Professor Tian Weiqian of Ocean University of China and Professor Yury Gogotsi of Drexel University in the United States, developed a high-strength composite film material with nanocellulose as the matrix material and high ionic/electronic conductivity. The material produces a reversible electrodialysis actuation effect in a low voltage field (±1 V) with a volumetric strain of more than 85%. The study, titled "Ultrastrong Ionotronic Films Showing Electrochemical Osmotic Actuation," is currently published in Advanced Materials. The research involves the cross-collaboration of scholars in materials science and engineering, electrochemistry, mechanical mechanics and other fields, including Dr. Jowan Rostami, Dr. Chen Bin, Dr. Farsa Ram, Dr. Tobias Benselfelt from the Royal Institute of Technology in Sweden, Associate Professor Torbjörn Pettersson, Professor Lars Wågberg, and Armin of Drexel University Dr. Vahid Mohammadi (now at Tesla) and Dr. Kyle Matthews participated in the study.
This work proposes a self-assembling composite membrane based on charged, high aspect ratio flexible nanocellulose fiber (CNF) and two-dimensional titanium carbide (MXene) nanosheets, with CNF and MXene arranged into layer structures during liquid-phase self-assembly and highly oriented within the membrane plane (Figure 1). MXene nanosheets have good electronic conductivity, and combine with CNF to form sheet structures and ion channels to achieve mixed ion/electronic conductivity, mechanical strength and water absorption. When the composite film is immersed in water or other solutions, a composite hydrogel with excellent mechanical properties can be formed (Figure 2). This work uses digital pattern correlation technology (DIC) to analyze the stress concentration phenomenon of composite films and their hydrogels, and explore the enhancement mechanism, which has a larger tensile strain at break and a more uniform strain distribution than composite films (Figure 3). The composite hydrogel can achieve reversible expansion/contraction by rapid electrochemical charge and discharge in NaCl solution, and the expansion rate can reach 85% when the potential difference is ±1 V and the charge and discharge time is 120 seconds. The mechanism of this phenomenon is explained by the change in osmotic pressure caused by the transport of electrons/ions in the hydrogel, which drives the water molecules to inhale or expel the hydrogel, resulting in reversible volume deformation (Figure 4).
Figure 1: (a) Schematic diagram of MXene-CNF composite film preparation; (b) AFM topography of the surface of the composite film; (c) Composite film SEM cross-sectional structure; (d) Two-dimensional spectra of X-ray diffraction; (e) One-dimensional X-ray diffraction peaks; (f) MXene aggregate sheet structure in composite films, apparent Scheller size.
Figure 2: Mechanical properties and mixed electron/ionic conductivity of composite films before and after expansion: (a) stress-strain curves of pure MXene film, pure CNF film, MXene-60% CNF composite film, and small size MXene-60% CNF composite film samples; (b) the proportion of liquid contained in the complex hydrogel after adequate expansion in water and 1 M NaCl solution; (c) Stress-strain curve of MXene-CNF composite hydrogel; (d) Ionic conductivity and electronic conductivity of composite hydrogels; (e) Comparison of this work with relevant research data of previous studies: ionic/electron hybrid conductivity and tensile strength of hydrogels; (f) Comparison of this work with previous related research data: electronic conductivity and tensile strength of hydrogels.
Figure 3: DIC analysis results: (a) stress distribution of MXene and CNF films in the initial tensile state and approaching fracture; (b) Stress distribution of MXene-40% CNF and MXene-60% CNF composite films in the initial tensile state and approaching fracture; (c) Stress distribution of MXene-40% CNF and MXene-60% CNF composite hydrogels in the initial tensile state and approaching fracture; The black arrows in the figure indicate where the material was finally fractured. (d) The degree of anisotropy in the stretching process, the film sample is labeled pure MXene film (1), MXene-20% CNF (2), MXene-40% CNF (3), MXene-60% CNF (4), MXene-20% CNF (5), pure CNF film (6); Composite hydrogel samples were labeled MXene-40% CNF (3-wet), MXene-60% CNF (4-wet), CNF (6-wet). (e) (f) Cross-sectional morphology of composite film and composite hydrogel SEM.
Figure 4: Electrochemical drive performance: (a) three-electrode device and electrochemical osmotic drive schematic; (b) Thickness change diagram of MXene-CNF composite hydrogel after charging and discharging; (c) the expansion ratio of hydrogel under different charge and discharge time conditions; (d) The molecular weight of water inhaled/discharged during the charging and discharging process. The new composite film combines good mechanical strength and electronic/ionic conductivity, and has potential applications in soft robots, artificial muscles and other fields. The authors of the paper are Associate Professor Tian Weiqian, Professor Lars A. Berglund and Associate Professor Max Hamedi, and the first authors are Dr. Li Laowan and Associate Professor Tian Weiqian. Professor Lars A. Berglund is currently a professor at the Department of Fiber and Polymer Engineering at the Royal Swedish Institute of Technology (KTH), an academician of the Royal Swedish Academy of Engineering, a well-known expert in the field of international bionanocomposites, and won the Anselme Payen Award, the highest international award in the field of cellulose and renewable resource materials in 2023. So far, he has supervised more than 30 doctoral students, published more than 150 papers in internationally renowned journals, and cited nearly 40,000 times. Dr. Li is currently a postdoctoral fellow in the team of Professor Lars A. Berglund of the Royal Institute of Technology in Sweden, focusing on polymer/nanocellulose matrix composites and X-ray diffraction. He has published more than 30 SCI papers, cited more than 600 times, and published more than 10 papers in internationally renowned journals such as Advanced Materials, ACS Nano, Carbohydrate Polymers as the first author/corresponding author. Dr. Tian Weiqian is currently an associate professor at the School of Materials Science and Engineering, Ocean University of China, and has been selected as a young expert of Taishan Scholars, a young youth of Shandong Province (overseas), and a second-level young talent project of Ocean University of China. Engaged in cellulose nanofibril-based flexible structure (electro-coupling) electrode self-assembly and application. He has published more than 60 SCI academic papers, which have been published in Advanced Materials (3 papers, 1 ESI highly cited, 1 front cover), Nature Communications, Chemical Engineering Journal (2 papers), Journal of Materials Chemistry A (2 papers, 1 ESI highly cited), Carbon (2 articles) and other journals, the H-index is 25, cited more than 2700 times, and the Chinese invention patent is 1. Some of the research results have been featured in Nature Reviews Materials 2019, 4(10), 625, and KTH News, Phys.org and other news. He has presided over 5 projects such as the National Natural Science Foundation of China, served as a reviewer for more than 10 international journals such as Science Advances, Matter, Advanced Functional Materials, and Carbon, and served as a young editorial board member of Rare Metals and Battery Energy. --Cellulose Recommended ---- Recommendation Number--
Paper Link:
https://doi.org/10.1002/adma.202301163 Source: Frontiers in Polymer Science