Marangoni propulsion in microscale systems – Principle and potential of transferring surface tension gradients into motion

• Applicant: Professorin Dr.-Ing. Clarissa Schönecker
• Subject Area: Fluid Mechanics
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 501107071

Flows in microscale systems, i.e. in geometries < 1mm, strongly depend on the properties of their interfaces. This is because the relative amount of interfaces is much larger in microscale systems than in larger geometries. Therefore, alternative propulsion methods are required or are more efficient. Marangoni stresses directly attack at interfaces. Therefore, they are ideal candidates for manipulating microscale flows. In this project, they are investigated with respect to their working mechanisms and their potential to serve as a basis for propulsion in microsystems. Furthermore, Marangoni stresses bear the attractive potential to convert light or heat into motion. The starting point of the investigations are newly developed concepts for the design of surfaces, and hence for the way in which Marangoni stresses can attack. Using these concepts, the physical principles of Marangoni propulsion in microsystems shall be understood. To achieve this goal, highly specific measurements of flow and temperature (using fluorescence correlation spectroscopy and confocal microscopy) will be combined with theoretical modelling and simulation of the coupled flow and heat transfer. Based on the so-gained understanding, strategies for efficient propulsion will be developed and their applicability will be assessed. This way, a basis for developing new propulsion mechanisms shall be provided. Throughout the project, two fundamental flow scenarios will be distinguished. First, for the case of a fluid moving along a stagnant solid, e.g. corresponding to a situation when fluid is pumped through a channel, the new concept makes use of a uniform heat source, whose heat is converted into motion. A uniform heat source will be of great advantage compared to existing strategies which involve temperature gradients along a surface, which are technically complex to implement. Also, already for these existing strategies, the physical foundations are not yet sufficiently understood. Second, for the case of a solid moving with respect to a stagnant liquid, which corresponds to the motion of a microswimmer or microparticle on a fluidic surface, two new concepts will be studied. Compared to existing propulsion strategies, they have the advantage that a uniform illumination is transferred into motion. This light-to-motion principle does not depend on any type of „fuel“, which would have to be transported along, nor does it depend on the presence of any chemicals, e.g. at the interface. Another current challenge for use of microparticles as microtransporters is the requirement to steer the transporters. To address this aim, a new strategy based on polarized light shall be tested.

• DFG Programme: Independent Junior Research Groups