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Soft Matter Incubator

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    Highly Efficient Oil-Water Separation Using Surface-Programmable Membranes
    (Georgia Institute of Technology, 2018-04-20) Zeng, Minxiang (Glenn) ; Zhang, Eric ; Huang, Dali ; Cheng, Zhengdong
    The challenge of separating emulsified oil from oil/water mixture has sparked enormous research interests in developing advanced membrane technology. One of the most crucial elements to achieve high separating efficiency lies in the design of unique interfacial properties of membranes. Herein, we present a surface-programmable membrane for separating oil-water emulsion based on contrast wetting strategy. Additionally, owing to the precise control on the surface chemistry and microstructures of membranes, the hybrid membrane not only separates the oil-water mixture with high efficiency (>99.2%), but also demonstrates versatility for multiple applications, e.g., heavy metal removal. This research opens up new opportunities in developing multifunctional membrane-based materials.
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    Local and Global Avalanches in Sheared Granular Materials
    (Georgia Institute of Technology, 2018-04-20) Zadeh, Aghil Abed ; Barés, Jonathan ; Behringer, Robert
    We perform a stick-slip experiment to characterize avalanches for granular materials. In our experiment, a constant speed stage pulls a slider which rests on a vertical bed of circular photoelastic particles in a 2D system. The stage is connected to the slider by a spring. We measure the force on the spring by a force sensor attached to the spring. We study the PDF of energy release and slip size, avalanche shape in time, and other seismicity laws during slip avalanches. We analyze the power spectrum of the force signal and probability distributions to understand the effect of the loading speed and of the spring stiffness on the statistical behavior of the system. From a more local point of view and by using a high speed camera and the photoelastic properties of our particles, we characterize the local stress change and flow of particles during avalanches. By image processing we detect the avalanches, as connected components in space and time, and the energy dissipation inside the granular medium and their PDFs. The PDFs of avalanches obey power laws both at global and local scales, but with different exponents. We try to understand the distribution and correlation of local avalanches in space and the way they coarse grain to the global avalanches.
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    Quantifying Hidden Order Out of Equilibrium
    (Georgia Institute of Technology, 2018-04-20) Chaikin, Paul
    While the equilibrium properties, states, and phase transitions of interacting systems are well described by statistical mechanics, the lack of suitable state parameters has hindered the understanding of non-equilibrium phenomena in divers settings, from glasses to driven systems to biology. Here we introduce a simple idea enabling the quantification of organization in non-equilibrium and equilibrium systems, even when the form of order is unknown. The length of a losslessly compressed data file is a direct measure of its information content [1]. Here we use data compression to study several out-of-equilibrium systems, and show that it both identifies ordering and reveals critical behavior in dynamical phase transitions. Our technique should provide a quantitative measure of organization in systems ranging from condensed matter systems in and out of equilibrium, to cosmology, biology and possibly economic and social systems.
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    Exploiting Disorder
    (Georgia Institute of Technology, 2018-04-20) Nagel, Sidney
    We are taught to understand solids by considering ideal crystals. This approach becomes untenable as the amount of disorder increases; for a glass with no well-defined long-range order, a crystal is an abysmal starting point for understanding the glass’s rigidity and excitations. Is there an alternative – the opposite of a crystal – where order, rather than disorder is the perturbation? Jamming is an alternate way of creating rigid solids that are qualitatively different from crystals. In a crystal with one atom per unit cell, all atoms produce the same response to external perturbations. Jammed materials are not similarly constrained and a new principle emerges: independence of bond-level response. Using networks where individual bonds can be successively removed, one can drive the system to different regimes of behavior. Consequently, one can exploit disorder to achieve unique, varied, textured and tunable response from auxetic to allosteric behavior.
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    Soft, Responsive and Semiconducting Gels
    (Georgia Institute of Technology, 2018-04-20) Rosu, Cornelia ; Russo, Paul S. ; Reichmanis, Elsa
    Interaction of biopolymers with organic electronic materials provides an appealing opportunity to design electroactive materials for use in many applications especially bioelectronics. Because of their biocompatibility, polypeptides do not act just as simple bio- components; rather they effectively influence the organization of π-conjugated polymers into highly crystalline structures that allow charge transport. The talk will focus on poly(γ-benzyl-L-glutamate), PBLG, a synthetic polypeptide that forms thermoreversible tree-dimensional networks. Blends with poly(3-hexylthiophene), P3HT, resulted in gel materials able to switch reversibly on and off their photo-physical properties. This behavior was observed during two cycles of heating-cooling-aging. Enhanced alignment of P3HT chains into J-aggregate structures, ideal for effective electronic performance, was attributed to interactions between the PBLG benzyl side chains and P3HT hexyl arms.
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    Ordered and Disordered Motion in Dense Active Materials
    (Georgia Institute of Technology, 2018-04-19) Berthier, Ludovic
    We discuss how the non-equilibrium driving forces introduced by the natural biological activity or by physical self-propulsion mechanisms generically affect the structure, dynamics and phase behavior of dense active media. We use theory and computer simulations to analyze simple models of such active materials. We borrow concepts from the equilibrium physics of amorphous and crystalline materials to provide a physical understanding of experimental observations performed with more complex systems such as self-propelled colloidal and granular systems, biological tissues, and bacterial colonies.
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    Cell Contraction Induces Long-Ranged Stress Stiffening in the Extracellular Matrix
    (Georgia Institute of Technology, 2018-04-19) Ronceray, Pierre ; Han, Yu Long ; Lenz, Martin ; Broedersz, Chase ; Guo, Ming
    Animal cells in tissues are supported by biopolymer matrices, which exhibit highly nonlinear mechanical properties. Here we show that this nonlinearity allows living contractile cells to generate a massive stiffness gradient in three distinct 3D extracellular matrix model systems: collagen, fibrin, and Matrigel. We decipher this remarkable behavior by introducing Nonlinear Stress Inference Microscopy (NSIM), a novel technique to infer stress fields in a 3D matrix from nonlinear microrheology measurement with optical tweezers. Using NSIM and simulations, we reveal a long-ranged propagation of cell-generated stresses resulting from local filament buckling. This slow decay of stress gives rise to the large spatial extent of the observed cell-induced matrix stiffness gradient, which could form a mechanism for mechanical communication between cells.
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    New Results for Old Physics: Critical Phenomena for Colloids in Microgravity
    (Georgia Institute of Technology, 2018-04-19) Weitz, Dave
    This talk will describe results from experiments conducted in the absence of gravitational forces allowing the effects very delicate interactions between colloidal particles to be explored. The behavior very close to the boundary of spinodal decomposition will be described.
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    Why is Structural Hierarchy So Prevalent in Biological Materials?
    (Georgia Institute of Technology, 2018-04-19) Michel, Jonathan ; Yunker, Peter J.
    Structural hierarchy, in which materials possess distinct features on multiple length scales, is ubiquitous in nature. Many biological materials, such as bone, cellulose, and muscle, have as many as ten hierarchical levels. While structural hierarchy confers many mechanical advantages, including improved toughness and economy of material, it also presents a problem as each hierarchical level substantially increases the amount of information necessary for proper assembly. This seems to conflict with the broad prevalence of naturally occurring hierarchical structures. At the present, there is no general framework for understanding the interplay between structures on disparate length scales; such a framework is a critical tool for accounting for the robustness of hierarchical materials to defects. Here, we use simulations and experiments to validate a generalized model for the tensile stiffness of hierarchical, stretching-stabilized networks with a nested, dilute hexagonal lattice structure, and demonstrate that the stiffness of such networks becomes less sensitive to errors in assembly with additional levels of hierarchy. Following seminal work by Maxwell and others on criteria for stiff frames, we extend the concept of connectivity in network mechanics, and find a similar dependence of material stiffness upon each hierarchical level. More broadly, this work helps account for the success of hierarchical, filamentous materials in biology and materials design, and offers a heuristic for ensuring that desired material properties are achieved within the required tolerance.
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    Fracturing of Marginally Stable Structures: Fiber Networks and Topological Metamaterials
    (Georgia Institute of Technology, 2018-04-19) Mao, Xiaoming
    When conventional brittle materials break, long cracks form due to stress focusing at crack tips: a phenomenon explained by Griffith in the 1920s. In this talk, we will discuss two types of systems where the fracturing process is “unconventional”. The first type are fiber networks. Using simulations we found that stress concentration never occurs in these networks. Instead, the network enters a steady state where force chains break and reform, leading to a divergent length scale. The second type are Maxwell lattices with domain walls hosting topologically protected states of self stress. Our simulations showed that stress and bond breaking events are concentrated on these domain walls, even in presence of cracks and deep into the nonlinear process of fracturing. We discuss how these ideas can be used in designing metamaterials that are protected against crack formation.