Smooth printing of viscoelastic microfilms with a flow focusing ejector

The flow focusing principle has recently been shown to successfully generate micrometer viscoelastic jets. In this technique, the liquid jet is gently extruded by the smooth suction caused by the acceleration in the discharge orifice of a coflowing gas stream. Nozzle clogging is a rare phenomenon in flow focusing because the emitted jet is much thinner than all the passages and orifices in the device. The Weber number characterizing the jet is very small, which reduces the liquid impact velocity when it is printed onto a substrate. In this article, we report the design, build, and characterization, for the first time, of a flow focusing ejector. Using an aqueous polyacrylamide solution, we examine the dependence of the diameter and velocity of the jet upon the ejector control parameters: injected flow rate, applied pressure drop, and distance from the discharge orifice. Moreover, we also study the deposition onto a glass substrate moving at a constant speed, paying attention to the influence that this parameter has over the printing quality. Finally, we illustrate the capabilities of the flow focusing ejector by printing lines of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) and polyvinylpyrrolidone, fluids commonly used in flexible electronics and tissue engineering, respectively.