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

摘要

We present an integrated microfluidic device for producing multiple steady steams of picoliter-sized droplets at kilohertz frequency rates. The device has a pressurized reservoir that feeds hundreds of active nozzles, each of which produces a continuous jet of fluid. The jets are inherently unstable, and can be individually thermally modulated at the orifice to produce droplets with a well-defined volume, at a consistent distance downstream from the nozzle. The thermal modulation at the orifice causes a variation in surface tension that propagates downstream inducing Marangoni instability, which is the underlying cause of drop formation. Controlled thermal modulation of each jet is achieved using CMOS/MEMS technology wherein a resistive heater element is integrated into the nozzle surrounding each orifice. In this presentation we discuss the operating physics of this device, methods for modeling its performance, and its application to high-speed continuous inkjet printing.