Liquid marbles: review of recent progress in physical properties, formation techniques, and lab-in-a-marble applications in microreactors and biosensors.

Liquid marbles (LMs) are nonsticking droplets whose surfaces are covered with low-wettability particles. Owing to their high mobility, shape reconfigurability, and widely accessible liquid/particle possibilities, the research on LMs has flourished since 2001. Their physical properties, fabrication mechanisms, and functionalisation capabilities indicate their potential for various applications.

When marbles challenge pearls.

The spectacular nature of non-wetting drops mainly arises from their extreme mobility, and quick-silver, for instance, was named after this property. There are two ways to make water non-wetting, and they both rely on texture: either we can roughen a hydrophobic solid, which makes drops looking like pearls, or we can texture the liquid with a hydrophobic powder that "isolates" the resulting marble from its substrate. We observe, here, races between pearls and marbles, and report two effects: (1) the static adhesion of the two objects is different in nature, which we interpret as a consequence of the way they meet their substrates; (2) when they move, pearls are generally quicker than marbles, which might arise from the dissimilarity of the liquid/air interface between these two kinds of globules.

Mechanically activated ionic transport across single-digit carbon nanotubes.

Fluid and ionic transport at the nanoscale has recently demonstrated a wealth of exotic behaviours. However, artificial nanofluidic devices are still far from demonstrating the advanced functionalities existing in biological systems, such as electrically and mechanically activated transport. Here, we focus on ionic transport through 2-nm-radius individual multiwalled carbon nanotubes under the combination of mechanical and electrical forcings.

Superhydrophobic frictions.

Contrasting with its sluggish behavior on standard solids, water is extremely mobile on superhydrophobic materials, as shown, for instance, by the continuous acceleration of drops on tilted water-repellent leaves. For much longer substrates, however, drops reach a terminal velocity that results from a balance between weight and friction, allowing us to question the nature of this friction. We report that the relationship between force and terminal velocity is nonlinear.

Two recipes for repelling hot water.

Although a hydrophobic microtexture at a solid surface most often reflects rain owing to the presence of entrapped air within the texture, it is much more challenging to repel hot water. As it contacts a colder material, hot water generates condensation within the cavities at the solid surface, which eventually builds bridges between the substrate and the water, and thus destroys repellency. Here we show that both "small" (~100 nm) and "large" (~10 µm) model features do reflect hot drops at any drop temperature and in the whole range of explored impact velocities.

Interfacial transport with mobile surface charges and consequences for ionic transport in carbon nanotubes.

In this paper, we explore the effect of a finite surface charge mobility on the interfacial transport: conductance, streaming currents, electro- and diffusio-osmotic flows. We first show that the surface charge mobility modifies the hydrodynamic boundary condition for the fluid, which introduces a supplementary term depending on the applied electric field. In particular, the resulting slip length is found to decrease inversely with the surface charge.

Antifogging abilities of model nanotextures.

Nanometre-scale features with special shapes impart a broad spectrum of unique properties to the surface of insects. These properties are essential for the animal's survival, and include the low light reflectance of moth eyes, the oil repellency of springtail carapaces and the ultra-adhesive nature of palmtree bugs. Antireflective mosquito eyes and cicada wings are also known to exhibit some antifogging and self-cleaning properties.

Capillary muscle.

The contraction of a muscle generates a force that decreases when increasing the contraction velocity. This "hyperbolic" force-velocity relationship has been known since the seminal work of A. V.