Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session B51: Invited Session: Frontiers of Soft Matter I |
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Sponsoring Units: GSOFT GSNP Chair: Randall Kamien, University of Pennsylvania Room: Grand Ballroom C1 |
Monday, March 2, 2015 11:15AM - 11:51AM |
B51.00001: Exploiting disorder for global response: Independence of bond-level response and selected-bond removal networks Invited Speaker: Sidney R. Nagel The properties of amorphous solids near jamming are qualitatively different from those of simple crystals [1]. In a crystal with only one atom per unit cell, all atoms play the same role in producing the solid's global response to an external perturbation; disordered materials are not similarly constrained. We will demonstrate a new principle that emerges for disordered matter: \textit{independence of bond-level response}. This independence refers not only to the dearth of strong correlations between the response of one bond compared to another, but also, and more importantly, to the variation of response of any specific bond to different external perturbations. Using \textit{selected-bond removal networks}, where individual bonds can be successively removed$,$ we demonstrate that one can drive the overall system to different regimes of behavior. Consequently one can exploit disorder to achieve unique, varied, textured and tunable global response. \\[4pt] [1] ``Solids between the mechanical extremes of order and disorder,'' C.P. Goodrich, A.J. Liu and S.R. Nagel \textit{Nature Physics} \textbf{10}, 578 (2014). [Preview Abstract] |
Monday, March 2, 2015 11:51AM - 12:27PM |
B51.00002: A theoretical framework for jamming in confluent biological tissues Invited Speaker: M. Lisa Manning For important biological functions such as wound healing, embryonic development, and cancer tumorogenesis, cells must initially rearrange and move over relatively large distances, like a liquid. Subsequently, these same tissues must undergo buckling and support shear stresses, like a solid. Our work suggests that biological tissues can accommodate these disparate requirements because the tissues are close to glass or jamming transition. While recent self propelled particle models generically predict a glass/jamming transition that is driven by packing density $\varphi $ and happens at some critical $\varphi $c less than unity, many biological tissues that are confluent with no gaps between cells appear to undergo a jamming transition at a constant density ($\varphi =$1). I will discuss a new theoretical framework for predicting energy barriers and rates of cell migration in 2D tissue monolayers, and show that this model predicts a novel type of rigidity transition, which takes place at~constant $\varphi =$1 and depends only on single cell properties such as cell-cell adhesion, cortical tension and cell elasticity. This model additionally predicts that an experimentally observable parameter, the ratio between a cell's perimeter and the square root of its cross-sectional area, attains a specific, critical value at the jamming transition. We show that this prediction is precisely realized in primary epithelial cultures from human patients, with implications for asthma pathology. [Preview Abstract] |
Monday, March 2, 2015 12:27PM - 1:03PM |
B51.00003: Arboreal solutions: diodes, pumps, and diggers inspired by trees Invited Speaker: Anette Hosoi Many natural systems have evolved to perform certain tasks -- climbing, sensing, swimming -- as perfectly as possible within the limits set by the laws of physics. This observation can be used both to guide engineering design, and to gain insights into the form and function of biological systems. In this talk we will consider both of these themes in the context of trees. Beginning with the roots, we examine the role of flexibility in moving through granular substrates. Next we discuss fluid transport in tall plants and finally we apply our findings to the design of engineered solid state pumps and diodes. [Preview Abstract] |
Monday, March 2, 2015 1:03PM - 1:39PM |
B51.00004: Mechanical Instabilities at Finite Temperature Invited Speaker: Xiaoming Mao The ``softness'' of soft materials often originates from their proximity to mechanical instabilities. Recent advances in soft matter research have revealed multiple classes of mechanical instabilities, featuring different scalings, different patterns of emergent rigid structure, and even different orders of rigidity transitions. These interesting behaviors have been observed in a wide range of systems, from granular packings to biological tissues and self-assembled structures. In this talk, we review this rich spectrum of behavior and discuss dramatic effects of thermal fluctuations near mechanical instabilities. We discuss a few ordered and disordered lattice models that represent different classes of mechanical instabilities, and show using analytic theories how thermal fluctuations lead to interesting finite-temperature phase diagrams in each case. In particular, (i) using a square lattice model that exhibits a mechanical instability towards exponentially many degenerate ground states, we show that fluctuations can drive the mechanical instability to a first-order transition, owing to divergent fluctuations near the isostatic point; and (ii) using two classes of disordered lattices, we show how under-coordinated random networks can be stabilized by fluctuations and discuss various regimes of unusual entropic rigidity, sharing similarities with jammed packings at finite temperature. [Preview Abstract] |
Monday, March 2, 2015 1:39PM - 2:15PM |
B51.00005: Soft interfaces: complex, dynamic, reacting and evolving Invited Speaker: Todd Squires Various surface-active species--ranging from small, amphiphilic molecules to proteins to colloidal particles--adsorb to fluid interfaces, enabling multiphase materials like foams and emulsions, biophysical structures like cell membranes and lung surfactant monolayers, and a host of novel two-dimensional materials more generally. Moreover, many such interfaces exhibit rich structural and dynamical properties, including the two-dimensional (surface) analogs of three-dimensional rheology, including viscoelasticity, shear thickening and thinning, and yield stresses. We have developed active interfacial microrheology techniques that simultaneously track the evolution of the microstructure of these complex interfaces, enabling morphology to be directly related to rheology. We will highlight particularly interesting two-dimensional materials, and will also discuss interfaces that evolve as surfactants adsorb (as occurs, e.g., in petrochemical emulsions, or protein solutions) or as reagents react (e.g. during interfacial polymerization reactions). In addition to probing the heterogeneity and mechanical properties of such evolving interfaces, we have developed techniques to visualize the evolution of bulk concentration fields as such reactions proceed, yielding new capabilities to probe reacting and evolving interfaces. [Preview Abstract] |
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