Marangoni effect inspired robotic self-propulsion over a water surface using a flow-imbibition-powered microfluidic pump

Abstract

Certain aquatic insects rapidly traverse water by secreting surfactants that exploit the Marangoni effect, inspiring the development of many self-propulsion systems. In this research, to demonstrate a new way of delivering liquid fuel to a water surface for Marangoni propulsion, a microfluidic pump driven by the flow-imbibition by a porous medium was integrated to create a novel self-propelling robot. After triggered by a small magnet, the liquid fuel stored in a microchannel is autonomously transported to an outlet in a mechanically tunable manner. We also comprehensively analyzed the effects of various design parameters on the robot’s locomotory behavior. It was shown that the traveled distance, energy density of fuel, operation time, and motion directionality were tunable by adjusting porous media, nozzle diameter, keel-extrusion, and the distance between the nozzle and water surface. The utilization of a microfluidic device in bioinspired robot is expected to bring out new possibilities in future development of self-propulsion system.

A Data‐Driven Review of Soft Robotics

“…Another exciting new publication discusses the Marangoni effect as a propulsion mechanism utilizing a surface tension gradient generated by the release of alcohol into the water on which a robot locomotes. [ 585 ]…”

“…Recent research exemplifies this notion with three different approaches: a combustion‐driven jumping robot that chemically creates its own hydrogen fuel from liquid metal, [ 584 ] a battery that can stretch and also bend at a radius of curvature of 10 mm, [ 598 ] and a soft robot that traverses across the surface of water propelled by a surface tension gradient via alcohol released from an onboard porous medium. [ 585 ]…”

“…Another exciting new publication discusses the Marangoni effect as a propulsion mechanism utilizing a surface tension gradient generated by the release of alcohol into the water on which a robot locomotes. [585] We note that many function media not only originate from alternate media (as in the case of Joule heating for thermal media and seen in fluidic actuation from a combustion reaction) but also can be inseparable from each other in the case of photothermal, electrothermal, or electromagnetic media. We restricted our data analysis for each robotic component to single data points of each category.…”

“…Recent research exemplifies this notion with three different approaches: a combustion-driven jumping robot that chemically creates its own hydrogen fuel from liquid metal, [584] a battery that can stretch and also bend at a radius of curvature of 10 mm, [598] and a soft robot that traverses across the surface of water propelled by a surface tension gradient via alcohol released from an onboard porous medium. [585] Figure 6b shows a majority of physical tethering for all component types except a power-providing robotic component. This apparent anomaly is sensible when considering that the main limiting factor in tethering is the ability to produce or contain power to deliver to all other robotic components on the device.…”

On-the-Fly Formation of Polymer Film at Water Surface

“…The first is a system for which the propellant container is the propelled object itself, or a system where the propellant reservoir is embarked on manufactured floats from which the directional release of the spreading liquid is the motion-determining parameter [ 24 ]. Second, a robot travelling on water based on a Marangoni propulsion system has been demonstrated using a flow-imbibition-powered microfluidic pump with a magnetic clamping to trigger the formation of alcohol droplets at required times [ 25 ]. The results obtained are very impressive but still require advanced technological expertise.…”