We present an experimental method to fabricate centimetric thin elastic capsules with highly uniform thickness and negligible bending stiffness using silicone elastomers. In our experiments, the capsules thickness is tunable at fabrication, while internal pressure and hoop (circumferential) stress are adjustable via hydrostatic inflation once the capsules are filled and immersed in water. Capsules mechanics are probed through hydro-elastic waves generated by weak mechanical perturbations at the capsule interface. By analyzing the surface wave dynamics in the Fourier domain, we extract the in-plane stress and demonstrate that the hydro-elastic waves are exclusively governed by hoop stress. This \reponse{provides a controllable macroscopic analogue of liquid drops} characterised by an effective surface tension, allowing the capsules to be modeled as large-scale ``elasto-drops'' with an inflation and thickness tunable effective surface tension. \reponse{In this limit, bending stiffness is negligible over the experimentally relevant wavelengths, so that the shell dynamics are governed primarily by in-plane tension.} Our work demonstrates that elasto-drops serve as a robust model system for parametric studies of large-scale \reponse{analogues of} liquid drops with experimentally adjustable surface tension.
Simple analytical relations for predicting pressure-deformation relations of drops/bubbles on capillaries with elastocapillary interfaces confirmed by Surface Evolver simulations.
We investigate freely expanding viscoelastic sheets. The sheets are produced by the impact of drops on a quartz plate covered with a thin layer of liquid nitrogen that suppresses shear viscous dissipation as a result of the cold Leidenfrost effect. The time evolution of the sheet is simultaneously recorded from top and side views using high-speed cameras. The investigated viscoelastic fluids are Maxwell fluids, which are characterized by low elastic moduli, and relaxation times that vary over almost two orders of magnitude, thus giving access to a large spectrum of viscoelastic and elastocapil…
Various materials are made of long thin fibers that are randomly oriented to form a complex network in which drops of wetting liquid tend to accumulate at the nodes. The capillary force exerted by the liquid can bend flexible fibers, which in turn influences the morphology adopted by the liquid. In this paper, we investigate, the role of the fiber flexibility on the shape of a small volume of liquid on a pair of crossed flexible fibers, through a model situation. We characterize the liquid morphologies as we vary the volume of liquid, the angle between the fibers, and the length of the fibers.…
This paper presents an electromechanical analysis of the nonlinear static response and the superimposed small-amplitude wave characteristics in an infinite periodic compressible dielectric elastomer (DE) laminate subjected to electrostatic excitations and prestress in the thickness direction. The enriched Gent material model is employed to account for the effects of strain stiffening and electrostriction of the DE laminate. The theory of nonlinear electroelasticity and related linearized incremental theory are exploited to derive the governing equations of nonlinear response and the dispersion…
Drops in contact with swollen, elastomeric substrates can induce a capillary-mediated phase separation in wetting ridges. Using laser scanning confocal microscopy, we visualize phase separation of oligomeric silicone oil from a crosslinked silicone network during steady-state sliding of water drops. We find an inverse relationship between the oil tip height and the drop sliding speed, which is rationalized by competing transport timescales of oil molecules: separation rate and drop-advection speed. Separation rates in highly swollen networks are as fast as diffusion in pure melts.
Elasto-capillarity at the nanoscale: on the coupling between elasticity and surface energy in soft solids
利用分子动力学模拟直接测量了液滴和气泡对软固体的毛细作用力。接触线附近的液体作用在固体上的力并不像通常假设的那样沿着液-汽界面取向，也不垂直于固体表面，而是指向液体。它表明，由这个力引起的弹性形变只能解释，如果相反的不可压缩的液体，表面应力是不同的表面能。利用热力学变分方法，我们证明了通过测量细长体在液体中的变形，可以精确地确定表面应力和表面能。从分子动力学获得的结果完全证实了最近通过实验获得的结果[Marchand等人，Phys. Rev. Lett. 108，094301（2012）]。
Rate of a reaction is enhanced by increase in temperature, partial pressure or the concentration of reactants, and/or via use of a catalyst or an enzyme. Whereas the former increases the probability of collision rate between different molecules, the latter provides an alternate reaction path that diminishes the activation energy barrier for reaction, both effects increase the reaction rate. The deformability of the substrate on which a reaction occurs is not known to affect this rate. In contrast, by carrying out reduction of Gold and Silver salt on soft, crosslinked layers of poly(dimethylsil…
Shell buckling is central in many biological structures and advanced functional materials, even if, traditionally, this elastic instability has been regarded as a catastrophic phenomenon to be avoided for engineering structures. Either way, predicting critical buckling conditions remains a long-standing challenge. The subcritical nature of shell buckling imparts extreme sensitivity to material and geometric imperfections. Consequently, measured critical loads are inevitably lower than classic theoretical predictions. Here, we present a robust mechanism to dynamically tune the buckling strength…
Motivated by the industrial processing of chocolate, we study experimentally the fluidisation of a sessile drop of yield-stress fluid on a pre-existing layer of the same fluid under vertical sinusoidal oscillations. We compare the behaviours of molten chocolate and Carbopol which are both shear-thinning with a similar yield stress but exhibit very different elastic properties. We find that these materials spread when the forcing acceleration exceeds a threshold which is determined by the initial deposition process. However, they exhibit very different spreading behaviours: whereas chocolate ex…
This contribution reports for the first time on fabrication and investigation of wetting properties of structured surfaces containing lamellae with an exceptionally high aspect ratio - height/width ratio demonstrated of 57:1. The lamellar surface was made using a polymer with tunable mechanical properties, and shape-memory behavior. It was found that wetting properties of such structured surfaces depend on temperature and thermal treatment history - lamellae are wetted easier at elevated temperature or after cooling to room temperature when the polymer is soft because of the easier deformabili…
