Simulation and Validation of Droplet Generation Process for Revealing Three Design Constraints in Electrohydrodynamic Jet Printing.

Yanqiao Pan,Liangcai Zeng

doi:10.3390/mi10020094

Abstract

Droplet generation process can directly affect process regulation and output performance of electrohydrodynamic jet (E-jet) printing in fabricating micro-to-nano scale functional structures. This paper proposes a numerical simulation model for whole process of droplet generation of E-jet printing based on the Taylor-Melcher leaky-dielectric model. The whole process of droplet generation is successfully simulated in one whole cycle, including Taylor cone generation, jet onset, jet break, and jet retraction. The feasibility and accuracy of the numerical simulation model is validated by a 30G stainless nozzle with inner diameter ~160 μm by E-jet printing experiments. Comparing numerical simulations and experimental results, period, velocity magnitude, four steps in an injection cycle, and shape of jet in each step are in good agreement. Further simulations are performed to reveal three design constraints against applied voltage, flow rate, and nozzle diameter, respectively. The established cone-jet numerical simulation model paves the way to investigate influences of process parameters and guide design of printheads for E-jet printing system with high performance in the future.

Highlights

Electrohydrodynamic jet (E-jet) printing [1,2,3,4] has been considered as a candidate to substitute traditional inkjet printing [5,6] for fabricating micro scale functional structures [7,8,9] that can be widely used in display [10], radio frequency identification (RFID) [11], and flexible sensors [12,13]
It is necessary to consider the following three design constraints when designing an E-jet printing printhead: (1) voltage constraint—applied voltage should be larger than the critical onset voltage; (2) flow rate constraint—the proper amount of solution should be continuously and stably supplied to the nozzle. (3) nozzle diameter constraint—if possible, a nozzle with a small diameter is demanded for achieving ultimate resolution of the micro functional structure
A numerical simulation model for the droplet generation process in E-jet printing is established based on the Taylor-Melcher leaky-dielectric model

Summary

Introduction

Electrohydrodynamic jet (E-jet) printing [1,2,3,4] has been considered as a candidate to substitute traditional inkjet printing [5,6] for fabricating micro scale functional structures [7,8,9] that can be widely used in display [10], radio frequency identification (RFID) [11], and flexible sensors [12,13]. In 1917, Zeleny [24] found a special phenomenon through experiments when a suitable electric field is applied between a hanging droplet and a substrate, the shape of the hanging droplet will change gradually from semi-sphere to cone due to electro-rheological effect, and a fine jet will burst from the tip of the cone To explain this unique phenomenon, scholars made some efforts on theoretical modelling. In 2006, Orest et al [30] successfully simulated the shape of a cone jet using Ansys CFX (4.4, Ansys, Canonsburg, PA, USA) and the corresponding user defined function (UDF) They found vortex distribution law in the flow field, but the simulation model was too simple and there was no jet break in the simulation. This study paves the way to investigate impacts of more process parameters and the guide design of printheads for E-jet printing systems with high performance in the future

Physical Model

Validation of Droplet Generation Process by Experiments

Influences of Controlling Parameters in E-Jet Printing

Conclusions