Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session C16: Focus Sesssion: Mechanical Singularities in Soft Matter IIFocus

Hide Abstracts 
Sponsoring Units: GSOFT GSNP Chair: Jasper van der Gucht, Wageningen University Room: 275 
Monday, March 13, 2017 2:30PM  2:42PM 
C16.00001: Void Collapse as a Platform for Observing the Effects of Strain Stiffening on Creasing Matthew Milner, Shelby Hutchens Creasing in soft materials occurs when initially flat surfaces are subjected to a critical field of strain, whereupon selfcontact occurs. In NeoHookean solids this has been predicted and observed to occur at a biaxial compressive stretch of 0.75, independent of modulus. More recently, theory predicts that constitutive response, specifically strain stiffening, plays a role in delaying crease onset to larger values of stretch [Jin & Suo, JMPS 2015]. We validate this prediction experimentally using a unique void collapse geometry in which water droplets embedded in PDMS are evaporated, placing the inner surface under biaxial compression. We analyze images of the collapsing droplet during evaporation to determine: void size reduction, crease onset, and crease evolution. The observed crease onset as a function of crosslinking ranges from a compressive stretch of $0.758\pm0.007$ to $0. 0.728\pm0.016$. Furthermore, we measure that the increased crosslinking over this range decreases the onset of limiting stretch, $J_{lim}$ from infinity (NeoHookean) to $J_{lim}=6.3\pm1.3$ (Gent model). Accounting for these experimentally determined limiting stretch values results in excellent agreement between theory and our experimentally observed crease onset, requiring no fitting parameters. [Preview Abstract] 
Monday, March 13, 2017 2:42PM  2:54PM 
C16.00002: How holes can reinforce soft solids Robert Style Normally embedding holes in a solid makes it softer. However, when the solid is small enough, the opposite can be true. We show this with soft composites (consisting of liquid droplets embedded in a soft silicone gel) which stiffen as the volume fraction of droplets increases. This is due to the surface stress of the gel/liquid interface. We also discuss the timedependent behaviour of these materials. [Preview Abstract] 
Monday, March 13, 2017 2:54PM  3:06PM 
C16.00003: Geometric singularities in the mechanics of strings and rods Harmeet Singh, James Hanna We will discuss propagating geometric discontinuities in onedimensional bodies, particularly those mediated by partial contact with obstacles that may serve as singular sources of momentum and energy. Invariance arguments and basic assumptions about contact interactions reveal counterintuitive behavior during pickup, laydown, impact, peeling, and other processes. Related phenomena can be found in string instruments, mooring lines, and many other systems. [Preview Abstract] 
Monday, March 13, 2017 3:06PM  3:18PM 
C16.00004: Combinatorial Design of Origami Strips Peter Dieleman, Scott Waitukaitis, Martin Hecke Combinatorial design of origami patterns holds great promise for creating shapeshifting materials. Here we will show that a previously overlooked symmetry in the folding motion of 4vertices can be exploited to create rigidly foldable origami patterns with unit cells containing an arbitrary number of vertices. Fold patterns with this symmetry can be constructed combinatorially, by adding together 2 by 2 vertex puzzle pieces. We will focus on a subclass of these patterns, which consists out of fold patterns with two folding branches. We will show that these two branches can be programmed such that they fold into the shape of 2 complexly curved, quasi 1D strips. Therefore, fold patterns in this subclass have the ability to shift from one preprogrammed shape, into another. [Preview Abstract] 
Monday, March 13, 2017 3:18PM  3:30PM 
C16.00005: An elastic dimpling instability with KosterlitzThouless character and a precursor role in creasing Tyler Engstrom, Joseph Paulsen, Jennifer Schwarz Creasing instability, also known as sulcification, occurs in a variety of quasi2d elastic systems subject to compressive plane strain, and has been proposed as a mechanism of brain folding. While the dynamics of preexisting creases can be understood in terms of crack propagation, a detailed critical phenomena picture of the instability is lacking. We show that surface \textit{dimpling} is an equilibrium phase transition, and can be described in a language of quasiparticle excitations conceptualized as ``ghost fibers" within the shear lag model. Tensioncompression pairs (dipoles) of ghost fibers are energetically favorable at low strains, and the pairs unbind at a critical compressive plane strain, analogously to vortices in the KosterlitzThouless transition. This dimpling transition bears strong resemblance to the creasing instability. We argue that zerolength creases are ghost fibers, which are a special case of ``ghost slabs". Critical strain of a ghost slab increases linearly with its length, and is independent of both shear modulus and system thickness. [Preview Abstract] 
Monday, March 13, 2017 3:30PM  3:42PM 
C16.00006: Dynamics in thin folded polymer films Andrew Croll, Damith Rozairo Origami and Kirigami inspired structures depend on a complex interplay between geometry and material properties. While clearly important to the overall function, very little attention has focused on how extreme curvatures and singularities in real materials influence the overall dynamic behaviour of folded structures. In this work we use a set of three polymer thin films in order to closely examine the interaction of material and geometry. Specifically, we use polydimethylsiloxane (PDMS), polystyrene (PS) and polycarbonate (PC) thin films which we subject to loading in several model geometries of varying complexity. Depending on the material, vastly different responses are noted in our experiments; Dcones can annihilate, cut or lead to a crumpling cascade when pushed through a film. Remarkably, order can be generated with additional perturbation. Finally, the role of adhesion in complex folded structures can be addressed. [Preview Abstract] 
Monday, March 13, 2017 3:42PM  3:54PM 
C16.00007: Poking pretensed elastic membranes: Regularization via a singularity Dominic Vella, Benny Davidovitch Indentation of thin elastic membranes is increasingly being used as a method of determining not only the elastic properties, but also the surface energy of such solids. Inspired by the indentation metrology of graphene and other very thin solids, which typically use an atomic force microscope or other small scale indenter, we study the idealized problem of the indentation of a pretensed elastic membrane. As might be expected, the limit of a point indenter has a singular stress field close to the point of indentation. However, this singularity is important for properly understanding the case of an indenter of small, but finite, size, and also regularizes an apparent softening of membranes as the indenter size shrinks. We then show that many previous experiments lie in an intermediate regime where the use of approximate analytical results leads to large relative errors and suggest how these problems might be avoided experimentally. [Preview Abstract] 
Monday, March 13, 2017 3:54PM  4:06PM 
C16.00008: Pattern zoology in biaxially prestretched elastic bilayers: from wrinkles and creases to fracturelike ridges Rashed AlRashed, Francisco Lopez JimĂ©nez, Pedro Reis The wrinkling of elastic bilayers under compression has been explored as a method to produce reversible surface topography, with applications ranging from microfluidics to tunable optics. We introduce a new experimental system to study the effects of prestretching on the instability patterns that result from the biaxial compression of thin shells bound to an elastic substrate. A prestretched substrate is first prepared by pressurizing an initially flat elastomeric disk and bulging it into a nearly hemispherical thick shell. The substrate is then coated with a thin layer of a polymer suspension, which, upon curing, results in a thin shell of nearly constant thickness. Releasing the prestretch in the substrate by deflating the system places the outer film in a state of biaxial compression, resulting in a variety of buckling patterns. We explore the parameter space by systematically varying the prestretch, the substrate/film stiffness mismatch, and the thickness of the film. This results in a continuous transition between different buckling patterns, from the dimples and wrinkles that are traditionally associated with the buckling of elastic bilayers, to creases and high aspect ratio `fracturelike' ridges, where the prestretch plays an essential role. [Preview Abstract] 
Monday, March 13, 2017 4:06PM  4:18PM 
C16.00009: Drop equilibrium on charged, elastic surfaces Haoyuan Jing, Shayandev Sinha, Siddhartha Das A liquid drop equilibrates on a partiallywetting, solid surface by selecting Young's angle as its contact angle. This simple picture gets altered in case the substrate is elastic. The resulting solid deformation ensures that the corresponding contact angle selection necessitates a combined macroscopic and microscopic description with the angles (both macroscopic and microscopic) demonstrating a behavior dictated by the Neumann's Law. Here we theoretically study the role of the presence of surface charges and the corresponding electric double layer (EDL) localized at the dropsoftsolid interface in dictating the corresponding drop equilibrium. This theoretical model, which is capable of quantifying the drop shape on a soft solid for the general case of $\gamma _{\mathrm{sl\thinspace }}$not equal to $\gamma_{\mathrm{sv}}$ in a thermodynamicallyconsistent framework, relies on the properties of the PDMS (polydimethylsiloxane) that has been the most widely used soft solid for quantifying such drop equilibrium. Our results reveal that (a) enhancement in the degree of ``softness" ensures that the equilibrium contact angles transit from the EDLmodified Young's law (rigid limit) to the EDLmodified Neumann's law (soft limit), (b) there is an increase in the softsolid deformation and apparent hydrophilicity of the drop with the EDL effects, and (c) the EDL effects become more significant when the soft solid is more hydrophilic to the drop. All these findings establishes the most remarkable ``softness'' enhancing capabilities of surface charges in the context of elastocapillarity. [Preview Abstract] 
Monday, March 13, 2017 4:18PM  4:30PM 
C16.00010: Singularities at contact: mechanics of a liquid drop on a solid film Benny Davidovitch, Dominic Vella Partial wetting of solid surfaces is a classical phenomenon, which underlies many elastocapillary problems. It is thus surprising that some key aspects of partial wetting create much confusion among workers in this field. At the heart of this confusion is the interplay of two kinds of singular processes: First matching three continuum phases at the contact line; Second doing so with vanishing strain for an ``inextensible'' solid phase. In this talk I will address the contact of a liquid drop on a thin, stiff solid film, suspended between fasteners or subjected to fixed tensile loads. In such a setup, the mechanics is doubly singular, reflecting high bendability together with near inextensibility of the film. Several groups suggested recently that the deformation of the film induced by the drop allows measuring the solidliquid and solidvapor surface energies, or a ``pretension'' in the suspended film. I will explain the fundamental error that underlies such proposals, and will describe a solution to this problem. Our solution employs singular perturbation theory, and takes into full consideration solid elasticity and surface energy. [Preview Abstract] 
Monday, March 13, 2017 4:30PM  4:42PM 
C16.00011: OxideMediated Fingering Instabilities in Liquid Metals Karen Daniels, Collin Eaker, David Hight, John O'Regan, Michael Dickey Fluid instabilities that form repeating, selfsimilar patterns are seen in a variety of natural and laboratory phenomena. Liquid metals are an unlikely candidate for these types of instabilities due to the large energetic penalty associated with increased surface area, yet these instabilities can be driven by electrochemical oxidation of a droplet in an aqueous solution. This oxidation lowers the effective interfacial tension of the metal, thereby inducing drastic and reversible shape changes in a galliumbased liquid metal alloy. We demonstrate via a boxcounting method that the fractal dimension (D = 1.3 $\pm$ 0.05) of the spreading metal places it in a different universality class than viscous fingering or diffusionlimitedaggregation (D = 1.713 $\pm$ 0.003). By characterizing the volume and electric potential dependency of the shape change over time, we show that a growing surface oxide layer both creates and suppresses instabilities. Promoting and suppressing these instabilities may be useful for shape reconfigurable electronic, electromagnetic, and optical devices that take advantage of the metallic property of the liquid. [Preview Abstract] 
Monday, March 13, 2017 4:42PM  4:54PM 
C16.00012: Anisotropic Exponents for Avalanche Correlation Lengths in SelfAffine Growth of Magnetic Domains Joel Clemmer, Mark Robbins Driven interfaces in a wide variety of systems undergo a critical depinning transition as the driving force is increased to a critical value, $F_c$. Near this transition, growth consists of discrete avalanches with a power law distribution of sizes and a diverging length scale along the interface $\xi_\\simF_cF^{\nu_\}$. Scaling theories often assume that correlations perpendicular to the interface diverge with an exponent $\nu_\perp = \alpha\nu_\$, where $\alpha$ is the selfaffine roughness exponent \footnote{O. Narayan, D. Fisher PRB 82 (1993)}. We simulate depinning of a selfaffine domain wall in the 3D random field Ising model to determine the ratio $\chi \sim \nu_\perp/\nu_\$. Analyzing individual avalanches show that the height $l_\perp$ and width along the interface $l_\$ scale as $l_\perp\sim l_\^\chi$ with $\chi=0.9\pm0.05$ over 3 decades in systems of $10^{10}$ spins. This value of $\chi$ is significantly greater than $\alpha\sim0.67$. Finite size scaling was used to confirm the value of $\chi$. The probability of reaching the top of a system of width $L$ and height $L^\chi$ as a function of $FF_cL^{1/\nu_\}$ collapses for $\chi=0.9\pm0.03$. We discuss the implications for other scaling relations and the conditions where $\chi$ and $\alpha$ should differ. [Preview Abstract] 
Monday, March 13, 2017 4:54PM  5:30PM 
C16.00013: Friction is Fracture: a new paradigm for the onset of frictional motion Invited Speaker: Jay Fineberg Friction is generally described by a single degree of freedom, a `friction coefficient'. We experimentally study the spacetime dynamics of the onset of dry and lubricated frictional motion when two contacting bodies start to slide. We first show that the transition from static to dynamic sliding is governed by rupture fronts (closely analogous to earthquakes) that break the contacts along the interface separating the two bodies. Moreover, the structure of these "laboratory earthquakes" is quantitatively described by singular solutions originally derived to describe the motion of rapid cracks under applied shear. We demonstrate that this framework quantitatively describes both earthquake motion and arrest. This framework also providing a new window into the hidden properties of the micron thick interface that governs a body's frictional properties. Using this window we show that lubricated interfaces, although~``slippery'',~~actually becomes tougher; lubricants significantly increase dissipated energy during rupture. The results establish a new (and fruitful) paradigm for describing friction. [Preview Abstract] 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit membership organization working to advance the knowledge of physics. 
© 2020 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
1 Research Road, Ridge, NY 119612701
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700