Influence of galvanic reaction parameters on Cu–Ag core–shell nanowires for piezoresistive strain sensing applications
摘要
In recent studies, high-aspect-ratio copper (Cu) and silver (Ag) nanowires (NWs) have emerged as promising materials for enhancing electrical conductivity in flexible electronic systems, owing to their ability to establish interconnected pathways within polymeric matrices. However, as a precious metal, Ag is expensive, while Cu oxidizes readily. This study presents a solution-phase process for synthesizing Cu–Ag core–shell nanowires (CuAgNWs) via galvanic replacement, aiming to combine the excellent oxidation resistance of Ag with the cost-effectiveness of Cu. Pure CuNWs have an average diameter of 50 nm. During galvanic replacement, increasing the reaction time, Cu:Ag molar ratio, and temperature resulted in thicker CuAgNWs with diameters up to 96 nm. This can be attributed to the enhanced Ag deposition on the {100} facets of the CuNWs, which correlates with the higher relative amounts of Ag determined by energy dispersive X-ray spectroscopy (EDS). Additionally, lower electrical resistance from 335.5 to 251.1 Ω was attained by the CuAgNWs with thicker Ag shells. This is due to the improved oxidation stability of the NWs and the contribution of Ag in the overall conductivity of the CuAgNWs. X-ray diffraction (XRD) reveals distinct peaks corresponding to Cu and Ag. Strong Cu peaks were observed, indicating excellent crystallinity. However, a flat and broad (200) Ag peak was identified from the XRD patterns of the CuAgNWs prepared at room temperature. Even at relatively high Ag concentration (up to 7.90 wt%), no other Ag peaks were present, possibly due to the thin Ag shell. This suggests the preferential deposition of Ag on the {100} facets of the CuNWs. The fabricated piezoresistive sensor, made from a CuAgNW film in a polydimethylsiloxane (PDMS) matrix, exhibited a low sheet resistance of 13 Ω/sq due to the presence of numerous conductive networks. The sensor displayed high sensitivity (0.8439 kPa−1) and a linear response under compressive stresses up to 1.6 kPa. The sensor was used to detect articular and muscular movements, exhibiting a stable electrical response in both strained and unstrained states. This demonstrates its suitability for wearable strain sensing applications.