(22e) Scalable Directed Assembly of Electrosprayed Nanoparticles By Durotaxis

Despite the ever-growing library of fabrication techniques, achieving scalability in the deliberate deposition of nanoparticles remains a challenge. We have demonstrated a method for the positioning of nanoparticles though a combination of liquid durotaxis and electrospray. Durotaxis describes the phenomenon wherein liquid droplets on flat, soft surfaces spontaneously move towards softer, or deeper, regions of the surface due to changes in the effective contact angle. By using a patterned hard substrate (here, a rigid plastic) coated by a soft overlayer (here, a silicone elastomer), the motion of microdroplets generated by an electrospray process is directed on the sub-micron scale during their evaporation. As a result, materials (e.g. dye, polymer, and nanoparticles) transported within the droplets are deposited in a spatially controlled manner. The final resulting pattern requires no direct patterning of the particles beyond the large-area electrospray and therefore represents a high-throughput technique. Additionally, the particle assembly has the benefit of being generated on a flat, conformable surface on a flexible patterned substrate. This latter factor is advantageous as it both allows for subsequent transfer printing of the materials and protects the underlying pattern from potentially damaging mechanical contact with the particles and transferred substrate, increasing its usable lifetime. This greatly increases the potential for scaling to a reel-to-reel process.