Freeze-dried silver nanowire based resin formulation for vat photopolymerization 3D printing of stretchable and electrically conductive nanocomposites

Abstract

Vat photopolymerization (VPP) 3D printing is well suited for high-throughput production of intricate parts, making it ideal for soft electronics fabrication. This necessitates the development of VPP-printed stretchable-conductive nanocomposites (VPP-SCN), which currently exhibit limited conductivities (<0.1 mS cm⁻¹) due to restricted conductive-filler concentration (CFC) to ensure resin’s printability and nanocomposite’s stretchability. Incorporating high aspect ratio (AR) conductive fillers can achieve superior conductivity at low CFC, but is hindered by ultrasonication-induced filler fractures in conventional dispersion methods. Herein, freeze drying is introduced to process high-AR silver nanowires, resulting in freeze-dried silver nanowires (f-AgNWs) that dispersible in resin via low-speed magnetic stirring, avoiding conventional ultrasonication. Due to their high AR, coplanar alignment of the f-AgNWs is induced during the layer-by-layer VPP process. This results in printed f-AgNW nanocomposites that exhibit anisotropic conductivity, with layer-perpendicular and layer-parallel conductivities of 5 mS cm⁻¹ and 110 mS cm⁻¹ respectively, demonstrating a significant enhancement over the existing VPP-SCN. The high AR of f-AgNWs facilitates the stated conductivity at low CFC of 5 wt%, preserving printability. Low CFC and AgNWs alignment also enable good stretchability (127 %), mechanical durability (32 %, 1000 cycles), and electrical stability (gauge factor = 1.38) of the nanocomposite. The achieved properties enable fully-printed functional applications, as demonstrated by a touch-detecting capacitive sensor, and a stretchable interconnect that maintains LED illumination under strain. This work provides valuable insights into achieving high conductivity without significantly compromising printability and stretchability, thereby enabling the potential utilization of VPP in the development and fabrication of soft electronics.