Electrospinner: Flexible wearable thermoelectric fibers: Combining wet spinning and triple processing to improve mechanical and power generation properties

Background

The booming development of smart wearable electronic products has significantly increased the demand for flexible wearable devices in many fields such as medical diagnostic equipment and smart watches, and also provided opportunities for the development of wearable flexible thermoelectric devices. As an important component of wearable flexible thermoelectric devices, flexible thermoelectric materials can directly convert thermal energy into electrical energy, and are simple to process and low in cost. Conductive polymers, represented by poly (3,4-ethylenedioxythiophene): polystyrene sulfonic acid (PEDOT:PSS), have the advantages of low thermal conductivity, non-toxicity, and adjustable conductivity. The fiber materials made of them have excellent flexibility and weavability. However, the thermoelectric performance of this material is not outstanding enough, which limits its promotion and application in the field of thermoelectric devices. Therefore, it is necessary to explore efficient and stable preparation methods to improve the thermoelectric performance of PEDOT:PSS fibers.

Recently, Professor Liu Qingfeng from Nanjing University of Science and Technology and Professor Chen Zhigang's team from Queensland University of Technology in Australia published a research result titled "Optimization of Wet-Spun PEDOT:PSS Fibers for Thermoelectric Applications through Innovative Triple Post-Treatments" in Advanced Fiber Materials.

The main point of this paper

In this work, silver nanoparticles/polyvinyl alcohol (AgNPs/PVA) were used as the core spinning solution, and polyurethane/dimethylformamide (TPU/DMF) was used as the skin spinning solution. Anisotropic conductive network (ACN@TPU) fibers were prepared by freeze-dried coaxial spinning (Figure 1a). ACN@TPU fibers have a hollow porous structure and exhibit high tensile strength, good flexibility and lightweight mechanical properties (Figure 1b-g).

During the freeze-dried coaxial spinning process, the AgNPs wrapped by PVA were uniformly dispersed into the porous TPU skin layer by using the concentration diffusion effect. From the SEM and EDS analysis results in Figure 2, it can be seen that the AgNPs are uniformly distributed along the fiber direction and gradually decrease in the direction perpendicular to the fiber.

From Figure 3, it can be seen that the strain sensor composed of ACN@TPU fiber, electronic universal testing machine and digital source meter can work stably under complex frequencies and strains. As a conceptual demonstration, the ACN@TPU fiber sensor can also accurately identify the large and small joint deformations of the dummy, indicating that ACN@TPU fiber has good application potential in the field of motion monitoring.

During the stretching of ACN@TPU fiber, the spacing of AgNPs along the fiber direction and perpendicular to the fiber direction changes differently (Figure 4a-c). Under strain, the spacing of AgNPs that originally overlapped each other along the fiber direction increases dramatically, showing high sensitivity (Figure 4d-e). Due to the positive Poisson's ratio of TPU material, the diameter of the fiber gradually decreases during the stretching process, and the AgNPs that originally showed a long distance dispersion perpendicular to the fiber direction overlap each other to form a new conductive network. The number of these newly generated conductive networks is positively correlated with the applied strain amplitude, thereby compensating for the resistance change caused by the severe breakage of the conductive network along the fiber direction, thereby showing good linearity.

In summary, strain sensing fiber is an ideal wearable material. The anisotropic conductive network fibers prepared by freeze-drying coaxial spinning strategy exhibit high sensitivity and linearity in a wide strain range, providing a useful reference for the preparation of high-performance wearable strain sensing fiber materials.

Electrospinning Nanofibers Article Source:

https://link.springer.com/article/10.1007/s42765-024-00441-5