Fabrication of color tunable patterns using aerodynamically focused nanoparticle system

Additive manufacturing-based patterning technologies have been actively explored for achieving simpler and more efficient fabrication and overcoming limitations of conventional patterning methods such as complex multistep processes and generation of toxic byproducts. To address this need, a novel solvent-free patterning system called aerodynamically focused nanoparticle (AFN) system was developed. This system utilizes aerodynamic control for precisely directing nanoparticle flow, thereby eliminating the need for solvents and post-processing. The AFN system demonstrated its ability to fabricate fine lines with a microsized width, narrower than the nozzle used, by adjusting air pressures for the two-step excitation and purging process.

In this study, the microsized patterns of tungsten trioxide were fabricated using an AFN system to fabricate a color-tunable (electrochromic) pattern. The pattern width and height were optimized by adjusting the scan times and jet pressure and analyzed using optical microscopy, a surface profiler, and scanning electron microscopy. Furthermore, the electrochromic performance evaluation confirmed the durability of AFN-patterned tungsten oxide lines, maintaining their stable operation without cracking or delamination for up to 500 coloration/bleaching cycles. The effective width of the pattern for color tuning was measured to be ∼91 μm, which is ∼14 % of the inner diameter (640 μm) of the nozzle, demonstrating that AFN can form patterns to be significantly narrower than that of the nozzle size via aerodynamically focusing process. This study highlights the contribution of the AFN system to advance electrochromic device technology by providing a highly precise and solvent-free method for electrochromic pattern formation.