Drops, Jets and High-Resolution 3D Printing: Fundamentals and Applications

Abstract

The ability to print high-resolution (< 10 µm) three-dimensional (3D) features is important in numerous existing and emerging applications such as tissue engineering, nanoelectronics, photovoltaics, optics, biomedical devices etc. The current chapter is focused on a subset of high-resolution printing techniques that exploit micro and nanofluidics features to attain high resolution. Here these approaches are referred as fluidics assisted high-resolution 3D printing. Salient examples of such techniques are electrohydrodynamic printing, direct-write assembly, aerosol jet printing, etc. The chapter starts with a brief introduction and discussion on the challenges of high-resolution printing. This is followed by a section on fundamental mechanisms of droplet, jet and filament formations, and their role in deciding the print resolution. Commonalities between different printing techniques (e.g. the physics of jet breakup and role of capillary stresses) are highlighted in order to provide a systematic understanding and context. Next the fluid mechanics features determining the print resolution and quality are discussed in detail. This includes sections on the role of ink rheology, evaporation rate, nozzle size, substrate and nozzle wetting properties (i.e. surface energy) and dynamic effects such as drop impact and spreading, stability of printed liquid lines and liquid filaments etc. Wherever relevant, literature on much more established inkjet printing techniques is also exploited to provide a context for the high-resolution printing and clarify the distinct benefits and challenges that emerge at progressively higher resolutions. In the wetting and surface energy section, features of dippen lithography and transfer printing, two popular techniques for two-dimensional high-resolution printing, are also briefly introduced for completeness. Lastly, the chapter ends with a summary and brief perspective on future research trends in this area.

Effect of Surface Roughness on Hydrodynamic Characteristics of an Impinging Droplet

“…1,2 The resultant wetting from the droplet−surface interactions is a central theme in many applications such as spray cooling, 3−5 spray coating, 6,7 spray combustion, 8 inkjet printing, 9 3Dprinting, 10,11 ceramics, 12 and metals. 13 The spreading behavior of droplets on dry surfaces is governed by a balance between the inertial, viscous, and surface tension forces. The droplet's spreading characteristics can have markedly different outcomes due to surface roughness and surface wettability through the contact angle it makes with the surface.…”

“…The resultant wetting from the droplet–surface interactions is a central theme in many applications such as spray cooling, − spray coating, , spray combustion, inkjet printing, 3D-printing, , ceramics, and metals …”

Embedded Core–Shell 3D Printing (eCS3DP) with Low-Viscosity Polysiloxanes

“…A previous study has demonstrated the use of custom-made nozzles with a microcapillary with minimum filament size down to 1 μm (with D c = 0.5–5 μm) . The decrease in D c causes a pronounced increase in pressure drop across the nozzle (Δ P ∼ 1/ D c 4 for Newtonian fluids) . The use of nozzles with small D c is therefore limited by the applicable pressure to the system.…”