Thermally Induced Marangoni Instability of Liquid Microjets with Application to Continuous Inkjet Printing

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Liquid microjets are inherently unstable and can be broken into droplets in a controllable fashion via thermal modulation of surface tension. Such modulation can be achieved using CMOS/MEMS technology by integrating resistive heating elements around each orifice of a microfluidic printhead. When the heating elements are modulated in a time-wise fashion, the thermal energy they produce diffuses into the microjet, and is carried downstream by the jet velocity. The time-wise thermal modulation results in a spatial variation of surface tension along the length of the jet, which induces Marangoni instability that ultimately causes breakup and drop formation. Based on this effect, novel microfluidic printheads have been fabricated with hundreds of orifices that can be individually modulated to produce steady streams of picoliter-sized droplets. These devices operate at kilohertz frequencies, and are capable of unprecedented speed of droplet generation. In this paper, we discuss thermally induced Marangoni instability and its application to continuous inkjet printing. We present a fabricated CMOS/MEMS printhead, and experimental data of its performance relative to jet instability and drop formation. We show sample prints obtained from the printhead, and compare the experimental data with analytical and CFD simulations

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Journal: TechConnect Briefs
Volume: 2, Technical Proceedings of the 2006 NSTI Nanotechnology Conference and Trade Show, Volume 2
Published: May 7, 2006
Pages: 534 - 537
Industry sectors: Medical & Biotech | Sensors, MEMS, Electronics
Topic: Micro & Bio Fluidics, Lab-on-Chip
ISBN: 0-9767985-7-3