Levitating clusters of fluorinated fumed silica nanoparticles enable manufacture of liquid marbles: Co-occurrence of interfacial, thermal and electrostatic events

We report non-contact coating of water droplets with levitating clusters of fumed silica nanoparticles placed on a heated substrate. The coating process results in the formation of liquid marbles. We relate the observed phenomenon to the electrostatic attraction between a water droplet and levitating clusters of fumed silica nanoparticles. A water droplet dispensed from a polymer (polypropylene) micropipette almost always have an intrinsic positive electrical charge which promotes electrostatic attraction of the levitating fumed silica powder to the droplet. The role of the natural convection of air is discussed. The clusters of fluorinated fumed silica nanoparticles gain their surface charge under contact with humid air. A qualitative phenomenological theory of the effect is suggested. Formation of composite marbles, built of water droplets coated with a silicone oil layer containing the clusters of fumed silica nanoparticles, is also demonstrated.