Abstract:

Objective Liquid metal-based conductive fibers offer several advantages, such as excellent electrical conductivity, and high stretchability, making them highly promising for smart textile applications. To enable the continuous fabrication of this kind of fiber, it is crucial to reduce the surface tension of the liquid metal and improve its interface adhesion. In this study, a liquid metal modification and fiber coating process was developed. Moreover the adhesion properties of the modified liquid metal composite paste were examined, as well as the electrical and mechanical properties of the resulting liquid metal composite fibers.

Method Nickel powder doping modification was used to prepare the liquid metal composite (LMC) paste with low surface tension and strong adhesion. This paste was then applied to the surface of silver-plated polyamide fibers through a coating process, enabling the continuous fabrication of LMC fibers. The morphology of these fibers was characterized, and their adhesion, mechanical, oxidation resistance, electrical, and electrothermal conversion properties were systematically investigated.

Results The surface morphology of three types of fibers(silver-plated polyamide fibers, liquid metal fibers(LM fibers), and LMC fibers)was examined using a super ultra-depth-of-field microscope. The experimental outcomes demonstrated that under identical coating procedures, the LM fibers had minute liquid metal droplets on their surfaces. In sharp contrast, the surfaces of the LMC fibers were uniformly covered with a compact layer of liquid metal composite paste. As a direct consequence of this coating, the diameter of the LMC fibers experienced a subtle augmentation, rising from an initial 223 μm to 248 μm. This study also investigated the effect of incorporating nickel powder into the liquid metal on its adhesion properties. When liquid metal and liquid metal composite paste were dropped onto the surface of an inclined glass plate, the liquid metal droplets slid off, while the liquid metal composite paste remained firmly in place. This suggests that the liquid metal modified with nickel powder has significantly improved adhesion properties. After coating the silver-plated polyamide fibers with the liquid metal composite paste, their electrical conductivity was greatly enhanced, achieving a conductivity of 4.8 × 10⁵ S/m,an impressive 728% increase compared to the uncoated silver-plated polyamide fibers. Moreover, the LMC fibers demonstrated excellent stability across various environments. When immersed in water for 1 h, or bent at different angles, the increase in resistance was only 1.9% and 0%, respectively, indicating that the LMC fibers possess strong environmental adaptability and stability. Stress-strain analysis of the three types of fibers revealed that the LMC fibers showed a slight reduction in tensile extensibility, but their overall performance remained comparable to that of the silver-plated polyamide fibers. These findings demonstrate that the coating of silver-plated polyamide fibers with liquid metal composite paste significantly improves their electrical conductivity and stability, while having minimal impact on their mechanical properties. Additionally, in three cycles of heating and cooling tests at a low voltage of 1.62 V, the fibers heated from 22.2 ℃ to 27.0 ℃ in just 15 s, further highlighting their excellent thermal responsiveness.

Conclusion This study successfully achieved the dynamic renewal of the surface oxide layer of liquid metal through nickel doping technology, resulting in a liquid metal composite paste with enhanced electrical conductivity and strong adhesion. By applying this paste to the surface of silver-plated polyamide fibers, LMC fibers with outstanding electrical conductivity and good flexibility were produced. The electrical conductivity of the LMC fibers reached 4.8×10⁵ S/m, with only 285 g of paste required to produce 10 km of fiber. Stress-strain tests demonstrated that coating the fiber surface with the liquid metal composite paste did not significantly compromise the mechanical properties of the fibers, ensuring their structural stability and reliability for practical applications. Additionally, the LMC fibers exhibited excellent stability in both bent states and underwater environments. Leveraging their electrothermal properties, these fibers can also be utilized as a solution for thermal management. In conclusion, the LMC fibers hold significant promise for applications in the field of smart clothing.

Key words: smart clothing, conductive fiber, liquid metal, composite paste, continuous preparation