Liquid Flow and Control Without Solid Walls

Solid walls become increasingly important when miniaturizing fluidic circuitry to the micron scale. They limit flow-rates due to friction and high pressure drop, and are plagued by fouling. Wall interactions have been reduced by hydrophobic coatings, porous surfaces, nanoparticles, changing the surface electronic structure, electrowetting, surface tension pinning, and atomically flat channels. We show wall-less aqueous liquid channels stabilised by a magnetic field that acts on a surrounding immiscible magnetic liquid. This creates self-healing, uncloggable, and near-frictionless liquid-in-liquid microfluidic channels that can be deformed and even closed without ever touching a solid wall. Basic fluidic operations including valving, mixing, and pumping can be achieved by moving permanent magnets. Our approach is compatible with conventional microfluidics, while opening unique prospects for nanofluidics without high pressures.