Electrospinner: Anisotropic conductive hollow fibers for flexible wearables: Development of freeze-dried coaxial spinning strategy to achieve highly sensitive and wide linear sensing!

Background

Strain sensing fibers are ideal materials for wearable strain sensors, and their sensitivity depends on the fracture amplitude of the conductive network under strain. However, when the highly sensitive conductive network breaks violently, a large number of non-uniform changes will occur, resulting in nonlinear changes in the sensing working curve, thus limiting the practical application of the fiber.

Recently, the team of Professor Du Zhaofang of Anhui Agricultural University published a research result entitled "Constructing Anisotropic Conductive Networks inside Hollow Elastic Fiber with High Sensitivity and Wide-Range Linearity by Cryo-spun Drying Strategy" in Advanced Fiber Materials, proposing a new strategy for freeze-drying coaxial spinning to construct anisotropic conductive network fibers. The content of the conductive material is consistent along the fiber direction and gradually decreases perpendicular to the fiber direction. Under strain, the conductive material along the fiber direction breaks violently, providing high sensitivity; the conductive material perpendicular to the fiber direction contacts each other to achieve good linearity. This study provides a useful reference for the preparation of high-performance strain sensing fibers.

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/s42765-024-00460-2