Dynamics of Liquid Transfer from Nanoporous Stamps in High-Resolution Flexographic Printing

Abstract

Printing of ultrathin layers of polymeric and colloidal inks is critical for the manufacturing of electronics on nonconventional substrates such as paper and polymer films. Recently, we found that nanoporous stamps overcome key limitations of traditional polymer stamps in flexographic printing, namely, enabling the printing of ultrathin nanoparticle films with micron-scale lateral precision. Here, we study the dynamics of liquid transfer between nanoporous stamps and solid substrates. The stamps comprise forests of polymer-coated carbon nanotubes, and the surface mechanics and wettability of the stamps are engineered to imbibe colloidal inks and transfer the ink upon contact with the target substrate. By high-speed imaging during printing, we observe the dynamics of liquid spreading, which is mediated by progressing contact between the nanostructured stamp surface and by the substrate and imbibition within the stamp−substrate gap. From the final contact area, the volume of ink transfer is mediated by rupture of a capillary bridge; and, after rupture, liquid spreads to fill the area defined by a precursor film matching the stamp geometry with high precision. Via modeling of the liquid dynamics, and comparison with data, we elucidate the scale-and ratelimiting aspects of the process. Specifically, we find that the printed ink volume and resulting layer thickness are independent of contact pressure; and that printed layer thickness decreases with retraction speed. Under these conditions, nanoparticle films with controlled thickness in the <100 nm regime can be printed using nanoporous stamp flexography, at speeds commensurate with industrial printing equipment.

Recent Advances in High-Throughput Nanomaterial Manufacturing for Hybrid Flexible Bioelectronics

“…As shown in Figure 3 b, the CNT nanopillars leave a precise open area in which the ink can reside. During printing, the stamp is brought into conformal contact with the substrate due to the mechanical flexibility of the CNTs, and a highly controlled deposition is produced as the stamp is removed, as shown in Figure 3 c. This mechanism overcomes many of the key challenges in flexographic transfer by storing the ink in the stamp pores, then transferring directly to the substrate, and yield high-quality prints with a variety of nanomaterial inks of <20 µm were demonstrated [ 60 , 61 ]. In light of these innovations, flexography is now considered an exciting new field in printed electronics with great opportunities for further improvement.…”

Nanoscale Patterning of Carbon Nanotubes: Techniques, Applications, and Future

“…[ 402 ] In a similar way, the patterned vertically aligned CNT forests can effectively hold ink and be used for high‐resolution flexographic patterning. [ 403 ] Nanoscale CNT electrodes can be fabricated by using AC DEP to bridge a CNT between larger electrodes, and then cutting the CNT with EB oxidation. [ 404 ] This provides an easy method to fabricate nanoscale electrodes with <20 nm gaps.…”

Droplet Dynamics and Freezing Delay on Nanoporous Microstructured Surfaces at Condensing Environment

“…Moreover, advancing WCA was observed to be 141 • in condensation condition (high humidity and low temperature), instead of 164 • in the dry condition. Understanding wettability and mechanisms of wetting transition are explicitly discussed on nanoporous surfaces [49,50]. Wang et al discussed the non-equilibrium condensed droplet morphologies by local energy barriers and nucleation-mediated droplet-droplet interactions, which leads to Wenzel state [42].…”