关键词: 聚氨酯, 微结构, 高灵敏度, 纤维转向, 柔性应变传感

Abstract: With the development of the artificial intelligence, the demand for flexible electronic devices is constantly increasing. Flexible resistive strain sensors, with a simple structure and fabrication process, can convert external mechanical stimuli into electrical signals, and exhibit high stretchability and adaptability, leading to wide utilization in smart wearables, medical diagnostics, soft robotics, and other fields. Traditional resistive strain sensors usually employ flexible polymer membranes as their substrate, but their poor breathability and water permeability reduce comfort of wearing, resulting in redness and even allergic reactions. Electrospun ultrafine fibers, characterized by their rich porosity, lightness, thinness, softness, and good conformability, are an ideal flexible electronic platform. However, ultrafine fibers obtained through conventional spinning processes are usually randomly or unidirectionally arranged. Under low strain conditions, fiber sliding buffers most of the strain, resulting in minimal changes in the morphology of the conductive layer and limited sensitivity. This problem greatly compromises the monitoring accuracy of the sensor and reduces its ability to capture valuable but small deformations and provide feedback.
To enhance the sensitivity of ultrafine fiber-based flexible strain sensors, a thermoplastic polyurethane (TPU) ultrafine fiber-based strain sensor with “furrow-ridge” structure was proposed. Firstly, a metal sheet array collector was designed to control the local fiber accumulation density and fiber alignment orientation under the driving force of the electric field, resulting in TPU ultrafine fiber substrate with a “furrow-ridge” structure. Subsequently, a highly sensitive flexible strain sensor was prepared by deposition of a brittle conductive silver (Ag) layer by using a fast and efficient spray coating technique. This method is simple and versatile, and can be used to prepare various electrospun fiber-based materials with a “furrow-ridge” structure, significantly enhancing sensitivity while maintaining a wide working range. It is found that the “furrow-ridge” structured ultrafine fiber substrate has orthogonal fiber alignment angles. This structure not only improves the tensile strength (13.26 MPa), elongation at break (355.81%), and elasticity (84.71%) of the fiber membrane, but also enhances local strain and induces significant changes in the morphology of the surface conductive layer material. Additionally, the unique fiber orientation guides the generation of cut-through cracks, leading to a sharp increase in electrical resistance and a significant improvement in sensitivity, with a maximum gauge factor reaching 151.36. The research can provide suggestions for the design and development of highly sensitive strain sensors and have broad prospects for applications in electronic skin, medical diagnostics, human-computer interaction, and other fields.

Key words: polyurethane, microstructure, high sensitivity, fiber orientation, flexible strain sensing