2, Dept of Chemical and Biological Engineering, The University of New Mexico, Albuquerque, New Mexico, United States
The development of printed and unconventional electronic devices to meet application-specific needs requires innovation in printing technologies. Flexography (flexo), a rubber-stamping method developed in the 19th century, has proven scalable (meters per second) for graphic arts but is underdeveloped for printed electronics, particularly transistor and transparent electrode applications, due to limited feature resolution (>50 µm).
Although much work has gone into understanding the structural and fluid mechanics of the ink transfer processes, little attention has been paid to the actual stamp, typically fabricated via polymer replication of a hard master. The elastomeric stamp is top-side inked and compressed on a substrate, a process that has inherent limits for materials transfer and results in uneven pixel quality (poor feature resolution) due to compression-induced spreading. However, consider a porous stamp that undergoes precise deformation such as negative Poisson’s ratio (NPR) during this process. Here, ink transfer could be a metered process with the pore-space being the reservoir and the mechanical deformation being the “metering pump”. Moreover, a stamp that exhibits a slight NPR may allow for controlled expulsion and sharper transfer foot print (minimal line-edge roughness). Only recently has it been feasible to produce such engineered structures at high resolution, for example, using multiphoton-induced, direct laser writing (DLW). Here we investigate how precisely architected (e.g., NPR and a structured pore size distribution), 3D porous media can control the fluid saturation/capillary pressure characteristics upon mechanical compression to enable high fidelity/metered material transfer for high speed printing. In this study, we systematically investigate the effects of porosity, pore size distribution and microstructure compression on flexographic ink transfer using iterative arrays of high-resolution (<1 µm feature size) DLW structures to converge on optimized forms. Fluid dynamics simulations of defined poroelastic media provide further insight into metering ink transfer during compression. Overall, this work illustrates the design flexibility and precision control of micro- features/fluid dynamics enabled using form-fabrication of flexographic forms.