Magnetic actuation of discrete liquid entities with a deformable paramagnetic liquid substrate

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Magnetic actuation of discrete liquid entities with a deformable paramagnetic liquid substrate, Angewandte Chemie (2017) 


We described a new mode of interfacial transport in which magnetic field-induced liquid substrate deformation was used to actuate floating objects. This is the first method that allows the magnetically controlled actuation and manipulation of discrete liquid entities in air, which does not rely on the use of magnetosensitive particles. It was demonstrated to be particularly versatile as it is compatible with both conventional drops and liquid marbles; and any liquid, including most common diamagnetic liquids such as oil and water, can be actuated. Deformation-based forces, especially capillary interactions, have been widely exploited to assemble or organize objects at interfaces, but deformation-based fluidic transport has been a much more rarely explored principle. From a fundamental point of view, we showed that the contribution of the substrate deformation, even within a range of only a few microns, largely dominated that of the magnetic force exerted on the transported object. This made it possible to actuate the system with cost-effective permanent magnets, paving the way for a new generation of microfluidic devices powered by miniature magnets and which are able to work without complex elements such as pumps, valves, or electrodes. This electric power-free principle can also contribute to expanding the possibilities of low-cost microfluidics and diagnostics, making solutions developed in laboratories more broadly available to people and societies.

Angewandte Chemie (2017) 


Because miniaturization is accompanied by an increase in the surface-over-volume ratio, most strategies for controlled manipulation of small-sized drops on substrates have relied on exploiting interfacial energy gradients, making it possible to actuate drops with various stimuli, including electrical or optical ones, but requiring adequate stimulus-responsive systems. In contrast, magnetic actuation of deposited drops has mainly relied on volume forces exerted on the liquid to be transported, which is poorly efficient with conventional diamagnetic liquids such as water or oil, unless magnetosensitive particles are added. Here, we describe a new way to magnetically control the motion of discrete liquid entities, in an additive-free and surface tension-independent manner. Our strategy consists of using a paramagnetic liquid as a deformable substrate to direct, using a magnet, the motion of various floating liquid entities, ranging from naked drops to liquid marbles. We demonstrate that, in our configuration, it is the substrate deformation that mainly dictates the behaviour of the floating liquid entity. We show that a broad variety of liquids, including diamagnetic (water, oil) and nonmagnetic ones can be efficiently transported using the moderate magnetic field (≈ 50 mT) produced by a cost-effective, cmsized permanent magnet. Complex trajectories can be achieved in a reliable manner and multiplexing potential is demonstrated through on-demand drop fusion. Our paramagnetofluidic method advantageously works without any complex equipment nor electric power, in phase with the necessary development of robust and lowcost analytical and diagnostic fluidic devices.

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Magnetic actuation of discrete liquid entities with a deformable paramagnetic liquid substrate


J. Vialetto, M. Hayakawa, N. Kavokine, M. Takinoue,  S. N. Varanakkottu, S. Rudiuk, M. Anyfantakis, M. Morel  and D. Baigl


Angewandte Chemie (2017)