Ni coating on cotton yarn by direct-write microdroplet deposition: microstructure and property

The application of metal coatings on cotton fiber surfaces has attracted significant attention in the field of flexible electronics. In this study, by combining an additive manufacturing platform with electroless plating, the authors successfully deposited nickel (Ni) coatings on cotton yarn by way of a direct-write microdroplet coating method, and systematically investigated the effects of deposition head speed and pass number on coating surface topography, microstructure, magnetic properties, flexibility, and corrosion resistance. The results indicate that increasing deposition head speed reduces coating smoothness, causes uneven particle distribution, and deteriorates coating-substrate adhesion; at a fixed head speed, more deposition passes improve coating density and magnetic properties. X-ray photoelectron spectrometer analysis revealed that a Ni²⁺ oxide and hydroxide dominated oxide film forms on the coating surface after atmospheric oxidation. Flexibility, electrochemical, and 3.5 wt.% sodium chloride (NaCl) immersion tests consistently show that the sample prepared at 20 mm/min with five passes achieves optimal flexibility and corrosion resistance, with the least mass loss and resistance change. This study provides a new method for the precise and controllable preparation of metal coatings on non-metallic material surfaces.