Hanging droplets from liquid surfaces

Significance Heavier objects usually sink in a less dense fluid. Water-walking anthropods and biomimetic water-walking robots harness surface tension in order to overcome this tendency, floating on top of liquids. By hanging a coacervate-encased droplet of a denser aqueous dextran solution from the surface of an aqueous solution of poly(ethylene glycol) (PEG), we harness the binding of dense droplets to interfaces by surface tension to build two-dimensional ensembles of structurally complex droplets. Applications ranging from reaction vessels with selective transport to motors and robotics are enabled by our findings.