Abstract:

Objective In recent years, liquid metals (LMs) have exhibited unique advantages in the preparation of stretchable conductive sensing fibers due to their excellent fluidity and electrical conductivity. To address the high surface tension of liquid metals, enabling them to stably combine with elastic matrices, efforts have been made to fabricate liquid metal-based conductive sensing fibers that possess both good electrical conductivity and flexibility while preventing leakage.

Method This study utilized the carboxyl groups in sodium alginate (SA) to coordinate with gallium ions in LM, forming a core-shell structure that enhances the interfacial wettability of LM. Subsequently, a stable and homogeneous spinning solution was prepared by incorporating waterborne polyurethane (WPU), enabling the production of SA-modified WPU/LM conductive sensing fibers via wet spinning technology. The influence of LM and SA mass fractions on the viscosity of the spinning solution and the mechanical and electrical properties of the SA-modified WPU/LM conductive sensing fibers were investigated,.

Results The results revealedthe proportional relation between the mass fraction of sodium alginate and the viscosity of the spinning solution. The spinning solution prepared by ultrasonically dispersing liquid metal with a sodium alginate mass fraction of 0.1% was found suitable for spinning, and the liquid metal in the spinning solution was evenly and stably dispersed. The relative resistance of sodium alginate-modified WPU/LM conductive sensing fibers within a tensile strain range of 0%-100% and tensile frequencies of 0.5-2 Hz exhibited periodical changes. During tensile loading, the relative resistance increased and resumed to the initial value upon recovery, demonstrating good resistance stability and sensitivity. During cyclic tensile tests, the relative resistance of sodium alginate-modified WPU/LM conductive sensing fibres responded with periodic changes. The relative resistance increased under tensile loading, and it decreased back to the initial value upon recovery, and the repeatable resistance response showed a resistance response time of 248 ms. In addition, The fabrics prepared by sodium alginate modified WPU/LM conductive sensing fibers (with a sensitivity value of 1.51)exhibited good electrical signal response characteristics in the signal monitoring of human joints and wrist pulses, suggesting applicability for human health monitoring. The research results indicated that the sensor fabric is able to respond to the strain of different parts of the human body in a timely manner, and the resistance changes at the elbow joint, knuckle and knee joint showed that when the joint was flexed the resistance change rate increased, and when the joint was straightened the resistance returned to the initial value. The sensor fabrics was show to quickly detect small changes in pulse signals in different states of the human body.

Conclusion The research results reveal that the SA-modified WPU/LM conductive sensing fibers exhibit exceptional mechanical performance, achieving a tensile elongation at break of up to 650%. Within the range of 0% to 100% tensile strain, under cyclic tensile tests at frequencies ranging from 0.5 to 2 Hz, the relative resistance change pattern of the conductive sensing fibers is characterized by an increase during stretching and a return to the initial value during recovery. These fibers demonstrate favorable resistance response characteristics and sensitivity, with a response time of 248 ms and a gauge factor sensitivity value of 1.51. Furthermore, they can sensitively monitor electrical signal variations associated with various human joint movements and wrist pulses under different conditions, showcasing potential applications in human health monitoring.

Key words: flexible sensing material, conductive fiber, liquid metal, waterborne polyurethane, sodium alginate, wet spinning, pulse monitoring, smart wearable textiles