Non-wetting drops at liquid interfaces: from liquid marbles to Leidenfrost drops

Abstract

We consider the flotation of deformable, non-wetting drops on a liquid interface. We consider the deflection of both the liquid interface and the droplet itself in response to the buoyancy forces, density difference and the various surface tensions within the system. Our results suggest new insight into a range of phenomena in which such drops occur, including Leidenfrost droplets and floating liquid marbles. In particular, we show that the floating state of liquid marbles is very sensitive to the tension of the particle-covered interface and suggest that this sensitivity may make such experiments a useful assay of the properties of these complex interfaces.

The engulfment of aqueous droplets on perfectly wetting oil layers

“…At the end of stage 1 (), all droplets sit at around the same height, , relative to the far-field oil level. This configuration is similar to the equilibrium lens state calculated numerically by Wong, Adda-Bedia & Vella (2017) for a perfectly non-wetting droplet on a liquid layer. By analogy, the presence of the air cushion in our experiments acts to make the droplet effectively non-wetting on the oil, and the state of the system at the end of stage 1 corresponds to an approximate balance between capillary stresses due to the deformed oil surface and the droplet's weight.…”

Self-propulsion of inverse Leidenfrost drops on a cryogenic bath

“…What could then cause the surface of the bath to deform? A hypothesis is that the symmetry breaking is generated by an instability of the morphology of the vapor film itself, which is very different from that of classical Leidenfrost drops over a flat rigid substrate (13,20). In particular, a recent theoretical study (27) shows that the film exhibits localized oscillations at the neck, which can develop within the whole film for drops smaller than the capillary length.…”

“…However, controlling drop motion seems more complex on deformable substrates such as liquid baths, where Leidenfrost levitation also occurs (13)(14)(15)(16)18). The liquid surface, resisting the weight of the drops is notably deformed (19,20), but this does not impact drop mobility, as there is no contact drag (21,22). The suspended drops were observed to sometimes glide for tens of seconds (14,16,18,23,24), and have to be trapped to perform some measurements (13).…”

Reactive silica nanoparticles turn epoxy coating from hydrophilic to super-robust superhydrophobic

“…Coating is an essential step in adjusting the surface properties of materials. 1 Superhydrophobic coatings have received much attention because of their applications in elds such as selfcleaning, [2][3][4] non-wetting liquids, 5 anti-icing [6][7][8] and oil-water separation. 7,8 A superhydrophobic coating surface is usually constituted by a combination of low surface energy substances and micro/nanometer scale roughness structures.…”