Thermal modulation and instability of newtonian liquid microjets

Abstract

Liquid microjets are inherently unstable and can be broken into droplets by various means including modulation of pressure, velocity, and/or fluid properties. In this presentation, we discuss the controlled breakup of viscous microjets via thermal modulation of surface tension. Such modulation has been implemented using CMOS/MEMS technology by integrating resistive heating elements around each orifice of a manifold as depicted in Fig. 1. When the heating elements are electrically pulsed, the thermal energy they produce penetrates the surface of the microjet, and is carried downstream to produce a spatial variation of surface tension along the length of the jet, which ultimately causes breakup and drop formation (Figs. 1 and 2). Using this process, microfluidic devices have been fabricated with thousands of individually modulated microjets that can produce steady steams of picoliter-sized droplets at kilohertz frequency rates [1]. In this presentation we review methods for analyzing such devices.