Mechanical robust and highly conductive composite hydrogel reinforced by a combination of cellulose nanofibrils/polypyrrole toward high-performance strain sensor

• Published in: Composites. Part B, Engineering Engineering, 2023-11, Vol.266, p.111022, Article 111022
• Main Authors: He, Xiao-Feng, Zeng, Zi-Fan, Ni, Qing-Yue, Xu, Zhi-Chao, Mao, Peng-Fei, Jiang, Baiyu, Wu, Qiang, Wang, Ben, Gong, Li-Xiu, Tang, Long-Cheng, Li, Shi-Neng
• Format: Article
• Language: English
• Subjects: Cellulose nanofibrils; Conductive hydrogel; Ionic/electronic conductive mechanism; Mechanical properties; Strain sensor
• ISSN: 1359-8368; 1879-1069
• DOI: 10.1016/j.compositesb.2023.111022

Although conductive and elastic materials are increasingly required for strain or stress sensing application in wearable electronic devices, it remains a great challenge to achieve outstanding and balanced mechanical performance while retaining high conductivity. Herein, the development of an ionic/electronic conductive hydrogel with mechanically robustness for strain sensors is reported. A covalently cross-linked polymer network is highly enhanced by a synergy of nano-enhancement (cellulose nanofibrils) and dynamic interactions containing hydrogen bonding and ionic coordination, which is used to support the mechanical structure of the hydrogel. By decorating with polypyrrole molecules via Fe3+ induced in-situ polymerization, the integrity of network structure is further improved by constructing physical interactions and chain entanglement. Therefore, compared to virgin poly(acrylamide-co-acrylic acid) hydrogel, the obtained hydrogel exhibits prominent mechanical performance containing high tensile strength (2.54 MPa) and ultra-high toughness (17.71 MJ m−3) along with remarkable stretchability (925%). Apart from Establishing a fair balance among mechanical parameters, a hybrid conductive path composed of ionic and electronic mechanism is also constructed simultaneously that results in an improved conductivity (995 mS m−1), wide working range (≈873%) and high sensitivity (maximum gauge factor: 25.6). Thus, the combination of outstanding mechanical performance and sensitive strain response makes the conductive hydrogel prepared herein apply for mechanically reliable and flexible strain sensor that can monitor diverse mechanical deformation (e.g., human joint movement) reflected by real-time resistance variation. Clearly, this work provides a new perspective for the design and fabrication of advanced gel-based materials aiming at high performance in human motion detection. [Display omitted] •The obtained hydrogel exhibits a well trade-off among the eminent integrated properties, i.e., mechanical robustness and sensing performance.•The synergy of multiple physical interactions, chain-entanglement and nano-reinforcement contributes to intriguing overall properties.•A sensitive strain-induced resistance change under multi-scale deformations can be achieved in such conductive hydrogel.•A hydrogel-based sensor displays a good applicability for variational deformation conditions.