Single droplet 3D printing of electrically conductive resin using high aspect ratio silver nanowires

The incorporation of silver nanowires (Ag NWs) in digital light processing (DLP) 3D printing enables the fast production of electrically conductive composites. The polyvinylpyrrolidone (PVP)-free polyol synthesized Ag NWs, in particular, exhibits high aspect ratio and requires less time in both synthesis and post processing as opposed to the conventional hydrothermal method. In this study, Ag NWs were synthesized in less than 30 min using the PVP-free polyol method. Long and thin pentagonal Ag NWs synthesized at 170 °C had the highest aspect ratio of around 1000 among the three temperatures examined. The as-synthesized Ag NWs were mixed directly with the liquid thermoplastic polyurethane (TPU) resin to produce electrically conductive resin. The optimum Ag NW loading was determined based on their printability and electrical performance. In order to achieve high precision and material utilization efficiency, a modified 3D printing process was proposed to fabricate a controllable 3D structure with single droplet of electrically conductive resin. A 3D printed structure with 1.3 wt% Ag NWs loading exhibited the highest electrical conductivity of 14 mS/cm. Additionally, the curing speed of the electrically conductive resin was enhanced by 450% with the introduction of 10 phr of photoinitiator. The 3D printed structure with the optimized electrically conductive resin formulation was able to light up an LED with 3.5 V applied and the IV characteristic revealed that the printed structure exhibited conductivity in the range of conductive materials (R = 13.7 kΩ).