Self-assembly and characterization of Marangoni microfluidic actuators

Abstract

We present a no moving parts fluidic actuator based on a solutal Marangoni effect which propels fluid in toroidal patterns. We show how to position the actuators at prescribed substrate locations by self-assembly and present experimental observations of the actuators in operation. We demonstrate how the actuators can be used to extend the range of capillary forces acting on a collection of submerged microfabricated parts leading to their self-assembly into larger structures. With one collection of microparts, a 250 µm radius actuator induced flow velocities of 5 mm s−1 in a water–ethanol solution. To explain and perform the predictive design of the actuators, we have developed a finite element model and obtained a good qualitative agreement with experimental observations. We calculated maximum non-dimensional velocities for Marangoni numbers (Ma) between 150 and 100 000, and found the velocities to follow a Ma0.695 power law, independent of Pr numbers between 530 and 1680. Both results agree with previous studies. These calculations allowed surface tension gradients in a particular experiment to be quantified, which led to the conclusion that the Marangoni actuators were equivalent to a 200 °C cm−1 thermocapillary effect operating at room temperature.