We consider natural and artificial hygromorphs, objects that respond to environmental humidity by changing their shape. Using the pine cone as an example opens when dried closes wet, we quantify geometry, mechanics dynamics of closure opening at cell, tissue organ levels, building on our prior structural knowledge. A simple scaling theory allows us hysteretic closing. also show how bilayer hygromorphs paper polymer similar behaviour can be quantified via a which couples fluid transport in...

Although negligible at large scales, capillary forces may become dominant for submillimetric objects. Surface tension is usually associated with the spherical shape of small droplets and bubbles, wetting phenomena, imbibition, or motion insects surface water. However, beyond liquid interfaces, can also deform solid bodies in their bulk, as observed recent experiments very soft gels. Capillary interactions, which are responsible cohesion sandcastles, bend slender structures induce bundling...

We describe how a wetting liquid brought into contact with forest of micropillars impregnates this forest. Both the driving and viscous forces depend on parameters texture (radius b height h pillars, pitch p network) it is found that two different limits characterize dynamics wicking. For small posts (h<p), film progresses all faster since are high, allowing simple control dynamics. tall pillars (h>p), speed impregnation becomes independent pillar height, mainly fixed by radius posts.

When surface wetting drives liquids to invade porous media or microstructured materials with uniform channels, the penetration distance is known increase as square root of time. We demonstrate, experimentally and theoretically, that shape variations channel, in flow direction, modify this ‘diffusive’ response. At short times, are not significant imbibition still diffusive. However, at long different power-law responses occur, their exponents uniquely connected details geometry. Experiments...

Adjusting the wetting properties of water through addition a miscible liquid is commonly used in wide variety industrial processes involving interfaces. We investigate experimentally evolution drop and volatile alcohol deposited on bath oil: The spreads spontaneously fragments into myriad minute droplets whose size strongly depends initial concentration alcohol. Marangoni flows induced by evaporation play key role overall phenomenon. intricate coupling hydrodynamics, wetting, well captured...

Lack of stiffness often limits thin shape-shifting structures to small scales. The large in-plane transformations required distort the metrics are indeed commonly achieved by using soft hydrogels or elastomers. We introduce here a versatile single-step method shapeprogram stiff inflated structures, opening door for numerous scale applications, ranging from space deployable emergency shelters. This technique relies on channel patterns obtained heat-sealing superimposed flat quasi-inextensible...

A soft solid is more easily sliced using a combination of normal and shearing deformations rather than diced by squeezing down on it normally with the same knife. To explain why this so, we experimentally probe slicing dicing agar gel wire, complement theory numerical simulations cutting highly deformable solid. We find that purely lead to global solid, so blade has penetrate deeply into sample, well beyond linear regime, reach relatively large critical stress nucleate fracture. In contrast,...

The crystal structure of atomically defined colloidal II-VI semiconductor nanoplatelets (NPLs) induces the self-assembly organic ligands over thousands square nanometers on top and bottom basal planes these anisotropic nanoparticles. NPLs curl into helices under influence surface stress induced by ligands. We demonstrate control radii NPL through described as an anchoring group aliphatic chain a given length. A mechanical model accounting for misfit strain between inorganic core predicts...

We investigate the mechanics of two asymmetric ribbons bound at one end and pulled apart other ends. characterize elastic junction near bonding conceptualize it as a bending boundary layer. While size this decreases with pulling force, we observe surprising existence binding angle macroscopic signature stiffnesses. Our results thus challenge standard assumption neglecting stiffness thin shells large tensile loading. In addition, show how rotational response structure exhibits nonlinear...

We study the effect of gravity on giant soap bubbles and show that it becomes dominant above critical size [Formula: see text], where text] is mean thickness film capillary length ([Formula: stands for vapor-liquid surface tension, liquid density). first experimentally large do not retain a spherical shape but flatten when increasing their size. A theoretical model then developed to account this effect, predicting based mechanical equilibrium. In stark contrast drops, we there no limit...

Significance Inflatable structures are flat and foldable when empty both lightweight stiff pressurized deployed. They easy to manufacture by fusing 2 inextensible sheets together along a defined pattern of lines. However, the prediction their deployed shape remains mathematical challenge, which results from coupling geometrical constraints strongly nonlinear asymmetric mechanical properties composing material: thin very on extensional loads, while they easily shrink buckling or wrinkling...

At short time, the rise of a viscous meniscus in capillary tube is opposed by dissipation at contact line, which leads to progression linear time instead classical Washburn dynamics only observed later, when liquid high enough.

Antibubbles are unusual fluid objects consisting of a thin spherical air shell surrounding liquid globule. Here we study and analyze the aging these inverted bubbles. The lifetime is found to be distributed along an exponential law. Moreover, breakdown film observed analogue dewetting by spinodal decomposition. We interpret long antibubbles as resulting from slow drainage until reaches critical thickness. Then, van der Waals forces act, leading collapse film.

The dynamics of break-up soap films is usually limited by an inertial resistance. We present here experimental results on the retraction a fluid sheet in viscous atmosphere. border film observed to form rim, which retracts at constant velocity. Contrasting with usual films, bursting friction arising from presence environment. A simple model developed explain these results.

We discuss here the nature of Landau-Levich transition, that is, dynamical transition occurs when drawing a solid out bath liquid partially wets this solid. Above threshold velocity, film is entrained by measure macroscopic contact angle between and different methods, conclude might be discontinuous at transition. also present model to understand fact shape meniscus as

Dielectric elastomer sheets undergo in-plane expansion when stimulated by a transverse electric field. We study experimentally how dielectric plates subjected to non-uniform voltage distribution buckling instabilities. Two different configurations involving circular are investigated: freely floating on bath of water, and clamped frame. describe theoretically the out-of-plane deformation within framework weakly non-linear plate equations. This constitutes first step route control 3D...

The velocity of a falling raindrop depends on its size, and thus so does shape. Here we describe the different simple shapes which model drops in air. While millimetric remain spherical, owing to action surface tension, larger than capillary length get flattened, as sessile solids. Air penetrates still globules, are observed be unstable. They inflate till they burst, generating myriads fragments.

We study the sedimentation of highly viscous droplets confined inside Hele-Shaw cells with textured walls controlled topography. In contrast common observations on superhydrophobic surfaces, roughness tends here to significantly increase friction, thus substantially decreasing mobility. However, reducing confinement induces a jump in velocity as can slide lubricating layer surrounding fluid thicker than features. demonstrate that increasing viscosity liquid may counterintuitively enhance...

We present experimental results on the extraction of oil trapped in confined region a wedge. Upon addition more wetting liquid, we observe that fingers develop into this extracting liquid. The eventually pinch off and form droplets are driven away from apex wedge by surface tension along gradient confinement. During an experiment, size expelled decreases as unstable front recedes towards show how can be predicted linear stability analysis reminiscent classical Saffman–Taylor instability....

Étienne Guyon nous a quittés en juillet dernier. Au cours de sa carrière, il eu une diversité impressionnante d’activités liées aux sciences comme lettres, à la recherche l’enseignement et diffusion scientifique. Les articles du présent dossier abordent quelques facettes cette : chercheur Orsay puis l’ESPCI, auteur 200 dans des revues internationales nombreux livres, directeur Palais découverte l’École normale supérieure, membre président particulièrement actif Société Française Physique.

This paper is associated with a video winner of 2017 APS/DFD Milton van Dyke Award for work presented at the DFD Gallery Fluid Motion. The original available from Motion, https://doi.org/10.1103/APS.DFD.2017.GFM.V0020

We show that ribbed elastic strips under tension present large spontaneous curvature and may close into tubes. In this single material architectured system, transverse bending results from a bilayer effect induced by Poisson contraction as the textured ribbon is stretched. Surprisingly, reverse if ribs of different orientations are considered. Slender structures also undergo nontrivial buckling transition. use analytical calculations to describe evolution morphology transitions between...