In recent years, flexible and scalable conductive devices have received increasing attention in the fields of supercapacitors, nano-generators, sensors, and electronic skin. Due to the limitations of elastic materials and embedded structures, in practical applications, these films cannot maintain long-term stable electrical performance under certain deformation states. Therefore, the research of the flexible conductive thin film device that can be fixed and deformed based on the shape memory function can solve the problem of the extension and stability of the practical application of the flexible electronic thin film device.
Recently, Zheng Xiaotong's group at Southwest Jiaotong University has obtained inspiration from the natural phenomenon that climbing vines twining bamboo stems can improve mechanical stability, and successfully prepared a nanofiber double-layer network structure with high elongation and shape memory. The characteristic polycaprolactone / polyethylene glycol / silver nanowire composite films (PPAFs), metallic silver nanowires are inserted into polymer fibers like a thread, forming an interpenetrating network structure that is intertwined (Figure 1). The bionic film has good and stable electrical conductivity. It can not only achieve reversible conduction of fixed shape and deformation in the stretching range, but also realize programmable characteristics between material resistance and deformation rate during the shape memory-recovery cycle. Therefore, this material has important application prospects in flexible devices and microcircuits.
Figure 1.Bionic PPAFs with interpenetrating network structure
As shown in Figure 2, when the film is subjected to a shape memory cycle experiment at the same deformation rate, its resistance has "memory characteristics", and the material is still in a conductive state within its elongation range. Conversely, when the same sample is continuously deformed with different elongations during the shape memory-recovery cycle (that is, pre-stretching, and the deformation rate during pre-stretching is lower than the secondary deformation rate), the resistance of the material There will be a sudden increase to the insulation state to achieve its own "conduction-insulation-conduction" conversion, which also provides a possibility for the material in the field of switch / conversion device applications.
（b）在拉伸率为10%、30%、50%时， PPAFs在变形周期内的电阻变化（c）在拉伸率为10%、30%、50%时，PPAFs在一个变形周期内的电阻变化（d）PPAF在不同拉伸率下电阻平均变化值（e）（f）PPAFs在不同变形率的连续变形下，电阻在变形周期内的变化 Figure 2 Resistance change of PPAFs (a) Change of resistance of PPAFs with bending times (b) Change of resistance of PPAFs during deformation cycles at elongation rates of 10%, 30%, and 50% (c) Change of elongation rate At 10%, 30%, and 50%, the resistance change of PPAFs in one deformation cycle (d) The average resistance change value of PPAF at different elongation rates (e) (f) PPAFs under continuous deformation at different deformation rates, Changes in resistance during deformation cycles
Based on the above resistance characteristics, through the microcircuit and proteus simulation design, PPAFs with programmable conductivity and memory cycle characteristics have been successfully applied in monitoring, switching and alarm devices.
Figure 3.PPAFs with a double-layer network structure
Application of PPAFs as monitoring devices
Figure 4 (a) Working schematic diagram of PPAFs as a detection device (b) Circuit diagram and (c) Real-time resistance and (d) Resistance change during operation
Application of PPAFs as conversion devices
Figure 5 (ah) schematic diagram of PPAFs as conversion devices and (i) real-time resistance and (j) resistance changes during operation
Application of PPAFs as alarm devices
Figure 6 (a, h) schematic diagram of PPAFs as alarm devices, (c) analog microcircuits, (d) alarm principle, (g) change relationship between film deformation rate and resistance, and (h) resistance during different shape memory cycles Curve
The important significance of this research is that a double-layered network structure is designed to interpenetrate, so that PPAFs with memory characteristics and ductility can achieve the functions of fixability, deformation and reversibility in a highly extended form. Through the design and application research of the multi-mode detection, conversion and alarm of the bionic composite film, the application prospect of the flexible conductive film with programmable characteristics is demonstrated.
Related research papers published:
Pandeng Tang, Xiaotong Zheng *, Huikai Yang, Jing He, Zhiwen Zheng, Weiqing Yang, Shaobing Zhou. Intrinsically Stretchable and Shape Memory Conducting Nanofiber for Programmable Flexible Electronic Films. ACS Appl. Mater. Interfaces 2019, DOI: 10.1021 / acsami.9b14430 .
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