Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session C18: Physics of Bio-inspired Materials IFocus
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Sponsoring Units: GSOFT DBIO Chair: Sung Hoon Kang Kyoo Chul Park, Johns Hopkins University, Northwestern University Room: 277 |
Monday, March 13, 2017 2:30PM - 2:42PM |
C18.00001: Polypeptide Liquid Crystal Assisted Assembly of Cylindrically Symmetric Silica-Polypeptide Hybrid Microparticles Paul Russo, Cornelia Rosu, Shane Jacobeen, Katherine Park, Peter Yunker, Elsa Reichmanis Liquid crystals can organize dispersed particles into exotic structures. Matching the particle surface coating to the chemistry of the mesogenic phase permits a tight focus on factors such as extended particle shape. The colloidal particles developed for this work consist of a magnetic and fluorescent cylinder-like silica core. One end of the silica is rounded, almost hemispherical, giving the particles a bullet-like shape. These particles are functionalized with helical poly($\gamma $-stearyl-L-glutamate) and dispersed, at different concentrations in cholesteric liquid crystals (ChLC) of the same polymer in tetrahydrofuran. Defects introduced by the particles to the director field of the bulk PSLG/THF host led to a variety of phases, including a quasi-hexagonal alignment of the particles. [Preview Abstract] |
Monday, March 13, 2017 2:42PM - 2:54PM |
C18.00002: Microstructures in a phase separating chiral membrane Raunak Sakhardande, Arvind Baskaran, Michael Hagan, Aparna Baskaran, Bulbul Chakraborty Chiral rod-like particles suspended in the presence of non-adsorbing polymer are driven by depletion interactions to form diverse high-order assemblies. Of particular interest are colloidal membranes, which is a one rod-length-thick monolayer of vertically aligned rods. Here, we discuss the phase behavior of colloidal membranes comprised of three rod species. One has a short length and right-handed chirality, the other two have long lengths and respectively right- and left-handed chirality. Experiments have shown that such a system undergoes microphase separation, with the short rods forming finite-sized domains floating in a background of the two long species. Tuning the background composition to be effectively achiral leads to complex, non-pairwise interactions between domains which exhibit multiple stable minima. We employ a Ginzburg-Landau description of the system to understand how this behavior depends on chirality and depletion interaction strength, and identify competing interactions which give rise to the complex inter-domain potentials. [Preview Abstract] |
Monday, March 13, 2017 2:54PM - 3:06PM |
C18.00003: Membrane rafts stabilized by chiral liquid crystal correction to bare interfacial tension Louis Kang, T. C. Lubensky Lipid rafts are hypothesized to facilitate protein interaction, tension regulation, and trafficking in biological membranes, but the mechanisms responsible for their formation and maintenance are not clear. Recently, experiments showed that bidisperse mixtures of filamentous viruses can self-assemble into colloidal monolayers with thermodynamically stable rafts that exhibit chiral structure and repulsive interactions. We quantitatively explain these observations by modeling the membrane particles as chiral liquid crystals. Chiral twist promotes the formation of finite-sized rafts by decreasing the effective interfacial tension between rafts and background membrane. It also mediates a repulsion that distributes rafts evenly throughout the membrane. Although this system is composed of filamentous viruses whose aggregation is entropically driven by dextran depletants instead of phospholipids and cholesterol with prominent electrostatic interactions, colloidal and biological membranes share many of the same physical symmetries. Chiral twist can contribute to the behavior of both systems and may account for certain stereospecific effects observed in molecular membranes. [Preview Abstract] |
Monday, March 13, 2017 3:06PM - 3:18PM |
C18.00004: Chiral edge fluctuations of colloidal membranes Leroy Jia, Mark Zakhary, Zvonimir Dogic, Robert Pelcovits, Thomas Powers Using experiments and theory we study chiral fluctuations of the edge of a nearly flat colloidal membrane, consisting of rod-like viruses held together by the depletion interaction. Our measurements show an anomalous peak in the power spectrum around 1 inverse micron. Using an effective theory to describe the liquid crystal degrees of freedom by geometric properties of the edge, such as length, geodesic torsion, and curvature, we calculate the spectrum of out-of-plane edge fluctuations. The peak arises for sufficiently strong chirality, and corresponds to the instability of a flat membrane to a shape with helical, rippled edges. [Preview Abstract] |
Monday, March 13, 2017 3:18PM - 3:30PM |
C18.00005: Stretching and twisting of colloidal membranes Thomas Powers, Leroy Jia, Robert Pelcovits Colloidal membranes consisting of rod-like virus particles held together by the depletion force form flat circular disks in the presence of a suitable concentration of polymer depletants. When subject to external forces, the disks transform into twisted ribbons. Making the assumption that the bending stiffness of the membrane is large, and therefore that the membrane has the shape of a minimal surface, we calculate the shape of the membrane as a function of applied force. Liquid crystalline degrees of freedom are accounted for using geometric properties of the edge such as length, curvature, and geodesic torsion. [Preview Abstract] |
Monday, March 13, 2017 3:30PM - 3:42PM |
C18.00006: Twisting in a new direction: Conformationally-tunable interactions of rafts in colloidal membranes Joia Miller, Prerna Sharma, Zvonimir Dogic Colloidal membranes composed of micron-long chiral rods provide a rich test system through which to study membrane properties. Specifically, we can study membrane-mediated interactions using self-assembled rafts of shorter rods suspended in a membrane. These rafts, composed of right-handed rods, display strong repulsive interactions when in a background membrane of left-handed rods driven by the chirality of the system. We find that tuning the net chirality of the membrane allows rafts to bind together into groups via an attractive interaction driven by conformational switching of rod orientation at the rafts' edge. [Preview Abstract] |
Monday, March 13, 2017 3:42PM - 4:18PM |
C18.00007: Bio-inspired active materials. Invited Speaker: Peter Fratzl Biological tissues are naturally interactive and adaptive. In general, these features are due to the action of cells that provide sensing, actuation as well as tissue remodelling. There are also examples of materials synthesized by living organisms, such as plant seeds, which fulfil an active function without living cells working as mechanosensors and actuators. Thus the activity of these materials is based on physical principles alone, which provides inspiration for new concepts for artificial active materials. We will describe structural principles leading to movement in seed capsules triggered by ambient humidity and discuss the influence of internal architecture on the overall mechanical behaviour of materials, including actuation and motility. Several conceptual systems for actuating planar structures will be discussed. [Preview Abstract] |
Monday, March 13, 2017 4:18PM - 4:30PM |
C18.00008: Mutation at Expanding Front of Self-Replicating Colloidal Clusters Hidenori Tanaka, Zorana Zeravcic, Michael Brenner We construct a scheme for self-replicating square clusters of particles in two spatial dimensions, and validate it with computer simulations in a finite-temperature heat bath. We find that the self- replication reactions propagate through the bath in the form of Fisher waves. Our model reflects existing colloidal systems, but is simple enough to allow simulation of many generations and thereby the first study of evolutionary dynamics in an artificial system. By introducing spatially localized mutations in the replication rules, we show that the mutated cluster population can survive and spread with the expanding front in circular sectors of the colony. [Preview Abstract] |
Monday, March 13, 2017 4:30PM - 4:42PM |
C18.00009: Strongly Modulated Friction of a Film-terminated Ridge-Channel Structure Anand Jagota, Zhenping He An anisotropic elastomeric surface comprising an array of ridges separated by channels of varying width and terminated by a thin film was found to have strongly tunable sliding friction. For small periodic spacing,, when motion is orthogonal to ridges, friction is significantly reduced, primarily due to deformation that causes loss of contact, a not-uncommon phenomenon for structured elastomeric surfaces. In sharp contrast, for a range of ridge-ridge spacing, we find surprisingly strong enhancement of sliding friction accompanied by a transition to complex sub-surface deformation modes, which is distinct from film-terminated fibrillar structures. However, when the motion is parallel to ridges, a different deformation pattern arises resulting diverse tribological performance. We elucidate the necessary conditions required to trigger these deformation modes and show that they enhance friction by creating multiple sliding internal interfaces and by unstable release of stored elastic energy. [Preview Abstract] |
Monday, March 13, 2017 4:42PM - 4:54PM |
C18.00010: Controlling Interfacial Separation in Porous Structures by Void Patterning Ahmed Ghareeb, Ahmed Elbanna Manipulating interfacial response for enhanced adhesion or fracture resistance is a problem of great interest to scientists and engineers. In many natural materials and engineering applications, an interface exists between a porous structure and a substrate. A question that arises is how the void distribution in the bulk may affect the interfacial response and whether it is possible to alter the interfacial toughness without changing the surface physical chemistry. In this paper, we address this question by studying the effect of patterning voids on the interfacial-to-the overall response of an elastic plate glued to a rigid substrate by bilinear cohesive material. Different patterning categories are investigated; uniform, graded, and binary voids. Each case is subjected to upward displacement at the upper edge of the plate. We show that the peak force and maximum elongation at failure depend on the voids design and by changing the void size, alignment or gradation we may control these performance measures. We relate these changes in the measured force displacement response to energy release rate as a measure of interfacial toughness. We discuss the implications of our results on design of bulk heterogeneities for enhanced interfacial behavior. [Preview Abstract] |
Monday, March 13, 2017 4:54PM - 5:06PM |
C18.00011: To leak or not to leak: elastic deformation induced by fluid loading in porous slender structures elizabeth strong, Hussain Karimi, Pedro M. Reis Fluid flow past thin, reticulated structures is common both in nature (e.g. spider webs, insect wings) and technology (e.g. fabric, wire fences). Whereas flow through porous media has been studied extensively, the problem of fluid loading of a porous, deformable structure with free boundaries has been much less explored. We use precision desktop experiments to investigate the specific, yet representative, fluid-structure interaction problem involving the deformation of a porous elastic plate towed in a fluid bath, across a range of low to moderate Reynolds numbers: 0.1 $\leq$ Re $\leq$ 10. In conjunction, we rationalize our observations and provide predictive guidelines for determining the drag force applied to porous plates using a reduced theoretical model. Specifically, we are interested in quantifying and understanding the effects that the porosity and the elasticity of the porous plate coupled with the fluid loading to dictate the equilibrium shapes of the deformed structure. [Preview Abstract] |
Monday, March 13, 2017 5:06PM - 5:18PM |
C18.00012: Curvature induced effects on undulatory waves in lower dimensional elastic structures. Jonathan Kernes, Alex J. Levine Nature abounds with a variety of lower dimensional elastic structures, such as stiff cytoskeletal filaments, cell membranes, graphene sheets, and carbon nanotubes. Understanding their thermal fluctuations demands that one account for the effect that curvature of the undeformed (i.e. elastic reference) state has on the mechanics of deformation.~This results from the fact that curvature couples in-plane stretching to bending even at linear order in deformation. We investigate the effects of this coupling by studying the~scattering of undulatory waves on elastic rods and membranes from local changes in curvature. We show that curved regions lead to strong backscattering of undulatory waves, suggesting localization induced by geometry. We also explore the ``tunneling'' of undulatory waves through high curvature regions, via their conversion into stretching modes. Finally,~we consider the undulatory wave band structure of periodically curved or corrugated elastic materials.~ [Preview Abstract] |
Monday, March 13, 2017 5:18PM - 5:30PM |
C18.00013: Folding dynamics of linear emulsion polymers into 3D architectures Angus McMullen, Dylan Bargteil, Jasna Brujic Colloidal polymers have been limited to inflexible, solid colloids. Here we show that the fluidity of emulsion droplets allows for the self-assembly of flexible droplet chains, which can subsequently be folded into 3D structures via secondary interactions. We achieve this using DNA-guided interactions, to initially form the chain, and then program its folding pathways. When two emulsion droplets labeled with complementary DNA meet, the balance of hybridization energy and droplet deformation yields an equilibrium patch size. Therefore, the concentration of DNA on the surface determines the number of droplet-droplet bonds in the assembly. We find that $96\%$ of bound droplets successfully self-assemble into chains. Droplet binding is a stochastic process, following a Poisson distribution of lengths. Since the fluid droplets can rearrange, we compare the dynamics of emulsion chains to that of polymers. We also trigger secondary interactions along the chain, causing the formation of specific loops or compact clusters. This approach will allow us to fold our emulsion polymers into a wide array of soft structures, giving us a powerful biomimetic colloidal system to investigate protein folding on the mesoscopic scale. This work was supported by the NSF MRSEC Program (DMR-0820341). [Preview Abstract] |
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