The paradox of contact angle selection on stretched soft solids

Can hydrodynamic contact line paradox be solved by evaporation--condensation?

We investigate a possibility to regularize the hydrodynamic contact line singularity in the configuration of partial wetting (liquid wedge on a solid substrate) via evaporation-condensation, when an inert gas is present in the atmosphere above the liquid. The no-slip condition is imposed at the solid-liquid interface and the system is assumed to be isothermal. The mass exchange dynamics is controlled by vapor diffusion in the inert gas and interfacial kinetic resistance. The coupling between the liquid meniscus curvature and mass exchange is provided by the Kelvin effect. The atmosphere is sat…

Two comments on adhesion

The adhesion paradox refers to the observation that for most solid objects no adhesion can be detected when they are separated from a state of molecular contact. The adhesion paradox results from surface roughness, and we present experimental and theoretical results which shows that adhesion in most cases is "killed" by the longest wavelength roughness. Adhesion experiments between a human finger and a clean glass plate were carried out, and for a dry finger, no macroscopic adhesion occurred. We suggest that the observed decrease in the contact area with increasing shear force results from non…

The Plateau-Rayleigh instability in solids is a simple phase separation

A long elastic cylinder, radius $a$ and shear-modulus $μ$, becomes unstable given sufficient surface tension $γ$. We show this instability can be simply understood by considering the energy, $E(λ)$, of such a cylinder subject to a homogenous longitudinal stretch $λ$. Although $E(λ)$ has a unique minimum, if surface tension is sufficient ($Γ\equivγ/(aμ)>\sqrt{32}$) it looses convexity in a finite region. We use a Maxwell construction to show that, if stretched into this region, the cylinder will phase separate into two segments with different stretches $λ_1$ and $λ_2$. Our model thus explains w…

软圆柱体中的弹性 Plateau-Rayleigh 不稳定性：表面弹性与周期性串珠

Elastic Plateau-Rayleigh instability in soft cylinders: Surface elasticity and periodic beading

本研究基于表面弹性理论，将表面张力视为预拉伸弹性表面，揭示了软圆柱体在足够软或轴向拉伸时会发生具有有限临界波长的周期性串珠不稳定性，为软材料等领域提供了新见解。

Mechanically Tunable Slippery Behavior on Soft Poly(dimethylsiloxane) (PDMS) Based Anisotropic Wrinkles Infused with Lubricating Fluid

We demonstrate a novel technique to fabricate mechanically tunable slippery surfaces using one dimensional (anisotropic) elastic wrinkles. Such wrinkles show tunable topography (amplitude) on the application of mechanical strain. Following Nepenthes pitcher plants, lubricating fluid infused solid surfaces show excellent slippery behavior for test liquid drops. Therefore combining the above two i.e. infusing suitable lubricating fluid on elastic wrinkles would enable us to fabricate mechanically tunable slippery surfaces. Completely stretched (flat) wrinkles have uniform coating of lubricating …

Normal stresses, contraction, and stiffening in sheared elastic networks

When elastic solids are sheared, a nonlinear effect named after Poynting gives rise to normal stresses or changes in volume. We provide a novel relation between the Poynting effect and the microscopic Grüneisen parameter, which quantifies how stretching shifts vibrational modes. By applying this relation to random spring networks, a minimal model for, e.g., biopolymer gels and solid foams, we find that networks contract or develop tension because they vibrate faster when stretched. The amplitude of the Poynting effect is sensitive to the network's linear elastic moduli, which can be tuned via …

Plastic Flow in Two-Dimensional Solids

A time-dependent Ginzburg-Landau model of plastic deformation in two-dimensional solids is presented. The fundamental dynamic variables are the displacement field $\bi u$ and the lattice velocity ${\bi v}=\p {\bi u}/\p t$. Damping is assumed to arise from the shear viscosity in the momentum equation. The elastic energy density is a periodic function of the shear and tetragonal strains, which enables formation of slips at large strains. In this work we neglect defects such as vacancies, interstitials, or grain boundaries. The simplest slip consists of two edge dislocations with opposite Burgers…

具有内应力的无热非晶固体弹性常数理论

Theory of elastic constants of athermal amorphous solids with internal stresses

本文基于非仿射晶格动力学提出含内应力的无热非晶固体弹性常数微观理论，解析解释内应力如何改变Maxwell刚性判据与剪切模量标度。

Computational mechanics of soft filaments

Soft slender structures are ubiquitous in natural and artificial systems and can be observed at scales that range from the nanometric to the kilometric, from polymers to space tethers. We present a practical numerical approach to simulate the dynamics of filaments that, at every cross-section, can undergo all six possible modes of deformation, allowing the filament to bend, twist, stretch and shear, while interacting with complex environments via muscular activity, surface contact, friction and hydrodynamics. We examine the accuracy of our method by means of several benchmark problems with kno…