Abstract:

Objective Metallized carbon nanotube (CNT) yarns are prepared and studied, which require the use of precious metals or complex processes to achieve satisfactory surface topography, resulting in high production costs. However, the mechanical properties of the metallized CNT yarns significantly are decreased while achieving the improved electrical conductivity. Therefore, it is necessary to find solutions that will enable metallized CNT yarns to have both satisfactory mechanical and electrical properties at low-cost.

Method This paper employed chemical deposition and electrochemical deposition methods to deposit metals on the surface of CNT yarns. Nickel served as the interface layer and oxidation-resistant layer in the metallized CNT composite yarns, while copper acted as the conductive layer. By adjusting the process parameters, controlling the process flow and adjusting the structure of the composite yarns, we successfully prepared high-performance Ni/Cu/Ni-CNT composite yarns. This paper conducted tests and characterizations on the mechanical, electrical, and processing properties of the composite yarns and discussed the influence of the nickel interface layer on the mechanical and electrical properties of the composite yarns.

Results The optimal electrochemical deposition was carried out at 5 mA/cm² for 180 min. The surface of the original CNT yarns exhibited prominent grooves, and the yarn surface was covered with metal, resulting in a significant reduction in the grooves after metal deposition. In the absence of a nickel interface layer, the surface of the composite yarn showed visible metal particles, with some copper loosely adsorbed onto the CNT yarns in the form of loose particles, leading to a rough and porous coating. However, with the presence of a nickel interface layer, the surface coating of the composite yarns became uniform and refined. The Ni/Cu/Ni-CNT composite yarns demonstrated a thicker coating compared to the Ni/Cu-CNT composite yarns without the nickel interface layer. However, the decrease in tensile strength of the Ni/Cu/Ni-CNT composite yarns was smaller than that of the Ni/Cu-CNT composite yarns, with an improved elongation at break. These findings indicate that the porous structure causes stress concentration, weakening the overall load-bearing capacity of the composite yarns and resulting in the deterioration of its mechanical properties. The nickel interface layer was introduced before the copper plating forms a robust CNT-Cu interface, for the purposes of enhancing the load efficiency between the CNT yarns and copper, improving the quality of the copper-plated layer, and creating tightly structured composite yarns with staisfactory mechanical properties. After copper plating, the electrical conductivity of the CNT yarns was significantly improved, with the Ni/Cu/Ni-CNT composite yarns exhibiting the best conductivity, which is 44 times higher than the original CNT yarns and 1.4 times higher than the Ni/Cu-CNT composite yarns. After 100 friction cycles, the surface of the Ni/Cu-CNT composite yarns suffered severe damage, with needle hook friction causing noticeable fractures in the metal coating. By contrast, the Ni/Cu/Ni-CNT composite yarns only exhibited micron-level cracks on the surface while maintaining a good surface topography. This indicates that the nickel interface layer significantly improves the wear resistance and knittability over the CNT/Cu composite yarns. After simulating 100 knitting cycles, the tensile strength of the composite yarns was slightly decreased, while the elongation at break got higher. The conductivity loss of the Ni/Cu-CNT composite yarns was 46%, while the Ni/Cu/Ni-CNT composite yarns showed a conductivity loss of 38%. Nonetheless, the conductivity loss was still 28 times higher than that of the original CNT yarns. Even after 100 friction cycles, the electrical conductivity of the composite yarns remained satisfactory.

Conclusion The Ni/Cu/Ni-CNT composite yarns prepared by chemical deposition and optimal electrochemical deposition exhibit excellent morphology, mechanical properties, and electrical properties. The surface coating of the Ni/Cu/Ni-CNT composite yarns is uniform and refined. Compared to the original CNT yarns, the Ni/Cu/Ni-CNT composite yarns show a 44-fold improvement in electrical performance while maintaining 90% of its tensile strength. The Ni/Cu/Ni-CNT composite yarns also demonstrate outstanding wear resistance and knittability. The nickel interface layer effectively enhances the adhesion of the copper-plated layer to the surface of the CNT yarns. After 100 friction cycles, only micron-level discontinuous cracks are observed on the yarn surface, and the tensile strength and electrical conductivity are maintained at 91% and 62%, respectively.

Key words: composite yarn, conductive material, carbon nanotube, surface metallization, interface enhancement, knittability, electrical property