Laser-actuated liquid delivery
Advanced printing applications require functional inks with complex physical properties. Today there are two main approaches to generate liquid droplets on demand: piezoelectric and thermal actuation. Their jetting mechanism is based on the generation of a pressure pulse to eject a small amount of incompressible liquid through a nozzle, hence producing one or more microdroplets.
The use of a nozzle sets a limitation on the range of printable inks, typically their viscosity is limited to 1–15 mPa.s. Higher-viscosity inks present significant challenges, as they tend to obstruct the nozzle and thus require a stronger pressure pulse to be jetted due to viscous dissipation. In addition, the characteristic achievable resolution, that is to say, the droplet diameter, is approximately equal to the nozzle diameter, which results in drop sizes on the order of 15–50 μm.
Recent studies showed that supersonic water jets can be generated by focusing a nanosecond laser pulse on an open water-filled glass capillary to induce a shockwave.
In this project, we adapt this laser-based jetting technique for the generation of low-velocity (1–2 m/s) flow-focused monodisperse microdroplets (80–200 μm) of a wide range of viscous liquids (2–200 mPa s) with the aim of broadening the range of functional materials that can be printed using DOD systems. In addition, our device is capable of generating monodisperse viscous droplets with a subnozzle resolution for nozzle diameters larger than 200 μm.
We demonstrated that this technique can be used to print biologically-relevant samples without degrading their functionality. Future work will focus on using structured light illumination to generate complex jets.
Laser-induced flow-focused micro-droplet of silver ink. The printing parameters are the following: the capillary (nozzle) diameter is 300 µm, the droplet diameter is 110 µm, the droplet velocity is 1 m/s and the laser energy is 25 µJ
Paul Delrot, Miguel A. Modestino, François Gallaire, Demetri Psaltis and Christophe Moser, “Inkjet Printing of Viscous Monodisperse Microdroplets by Laser-Induced Flow Focusing,” Physical Review Applied 6, no. 2 (August 8, 2016): 024003, doi:10.1103/PhysRevApplied.6.024003.