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Center for the Science and Technology of Advanced Materials and Interfaces

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    How Hidden Geometric Symmetries in Origami Generate New Folding Mechanisms
    (Georgia Institute of Technology, 2018-04-19) McInerney, James ; Rocklin, D. Zeb ; Georgia Institute of Technology. Center for the Science and Technology of Advanced Materials and Interfaces ; Georgia Institute of Technology. School of Physics
    The traditional Japanese art of paper folding has inspired various foldable materials, some now realizable at the atomic scale. These thin sheets use engineered crease patterns to provide a desired mechanical response governed by the crease pattern geometry. We consider the entire class of triangulated origami, where global symmetries come paired with force-bearing modes that correspond to linear folding motions. We find triangulated origami generally has two such folding modes that extend into the non-linear regime and transform the origami sheet into cylindrical sections. The key feature of this class of origami is its matching number of constraints and degrees of freedom; hence, our methods are applicable to sheets allowing cuts and folds called kirigami, and continuous sheets satisfying this condition.
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    Ordered and Disordered Motion in Dense Active Materials
    (Georgia Institute of Technology, 2018-04-19) Berthier, Ludovic ; Georgia Institute of Technology. Center for the Science and Technology of Advanced Materials and Interfaces ; Centre national de la recherche scientifique (France) ; Université de Montpellier ; University of Montpellier
    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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    The Topological Character of Smectics
    (Georgia Institute of Technology, 2018-04-18) Kamien, Randy ; Georgia Institute of Technology. Center for the Science and Technology of Advanced Materials and Interfaces ; University of Pennsylvania. Department of Physics and Astronomy
    Though the systematic use of topology to understand defects in ordered matter is now nearly 50 years old, the original work failed to completely characterize systems with broken translational order, i.e., crystals. Smectics are the simplest example of crystals and we have employed new mathematical tools to study and classify the allowed point and line defects in them. The theory reduces to the time-honored homotopy theory if we ignore the periodic order of the smectic but offers a refinement -- though the smectic can support all the defect structure and algebra of the nematic phase that sits above it, the defects have further structure that we have uncovered. This has allowed us to understand previously open puzzles, including the nature of composite dislocations in smectics.
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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 ; Georgia Institute of Technology. Center for the Science and Technology of Advanced Materials and Interfaces ; Princeton University
    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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    Scaling down the laws of thermodynamics
    (Georgia Institute of Technology, 2018-11-14) Jarzynski, Christopher ; Georgia Institute of Technology. Center for the Science and Technology of Advanced Materials and Interfaces ; Georgia Institute for Technology. Community for Research on Active Surfaces and Interfaces ; University of Maryland, College Park. Dept. of Chemistry and Biochemistry
    Thermodynamics provides a robust conceptual framework and set of laws that govern the exchange of energy and matter. Although these laws were originally articulated for macroscopic objects, it is hard to deny that nanoscale systems, as well, often exhibit “thermodynamic-like” behavior. To what extent can the venerable laws of thermodynamics be scaled down to apply to individual microscopic systems, and what new features emerge at the nanoscale? I will review recent progress toward answering these questions, with a focus on the second law of thermodynamics. I will argue that the inequalities ordinarily used to express the second law can be replaced by stronger equalities, known as fluctuation relations, which relate equilibrium properties to far-from-equilibrium fluctuations. The discovery and experimental validation of these relations has stimulated interest in the feedback control of small systems, the closely related Maxwell demon paradox, and the interpretation of the thermodynamic arrow of time. These developments have led to new tools for the analysis of non-equilibrium experiments and simulations, and they have refined our understanding of irreversibility and the second law.
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    Disorder-Order Transitions in p-Conjugated Polymers
    (Georgia Institute of Technology, 2016-12-02) Köhler, Anna ; Georgia Institute of Technology. Center for the Science and Technology of Advanced Materials and Interfaces ; University of Bayreuth ; Universität Bayreuth
    The aggregation of p-conjugated materials significantly impacts on the photophysics, and thus on the performance of optoelectronic devices. Nevertheless, we know comparatively little about the laws governing aggregate formation of p-conjugated materials from solution. In this talk, I shall compare, discuss and summarize how aggregates form for three different types of compounds, that is, homopolymers, donor-acceptor type polymers and low molecular weight compounds. To understand how aggregates form, we employ temperature dependent optical spectroscopy, which is a simple yet powerful tool for such investigations. I shall discuss how optical spectra can be analysed to identify distinct conformational states and to obtain quantitative information on changes in the inter-chain coupling, the conjugation length and the oscillator strength upon aggregate formation. We find aggregate formation to proceed alike in all these compounds by a coil-to-globule like first order phase transition. Notably, the chain expands before it collapses into a highly ordered dense state. I will address the role of side chains and the impact of changes in environmental polarization.
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    What Topology Reveals About Real Systems
    (Georgia Institute of Technology, 2018-05-11) Rocklin, D. Zeb ; Georgia Institute of Technology. Center for the Science and Technology of Advanced Materials and Interfaces ; Georgia Institute of Technology. School of Physics
    A tutorial intended to introduce topology with a minimum of math and provide a background as to how it applies to real systems such as those considered in the Workshop on Topological Protection in Messy Matter.
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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 ; Georgia Institute of Technology. Center for the Science and Technology of Advanced Materials and Interfaces ; Texas A & M University
    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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    Self–Assembled DNA Liquids: Properties and Protein Activation
    (Georgia Institute of Technology, 2018-04-19) Saleh, Omar ; Georgia Institute of Technology. Center for the Science and Technology of Advanced Materials and Interfaces ; University of California, Santa Barbara
    Biomolecules can self-assemble into liquid phases, termed ‘membraneless organelles’ in the biological context, though also known as ‘coacervates’. I will discuss our efforts to study this by exploiting DNA nanotechnology to create DNA particles that phase separate into liquids. Formation of liquids, rather than gel aggregates, depends sensitively on the internal flexibility of the DNA particles. Our engineered system displays unusual properties, including the ability to create several distinct liquid phases in a single solution, and to tailor interactions between the phases. Further, the reduced valency of the particles, along with the relatively stiff nature of the constituent DNA strands, causes the liquid to be extraordinarily sparse, with a DNA volume fraction of only ~2%. This opens the possibility to activate the material by infusion of the liquid with proteins; I will discuss our initial attempts at doing this.
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    Layered and Fibrillar Polymeric Systems by NanoExtrusion Forced Assembly
    (Georgia Institute of Technology, 2016-11-07) Baer, Eric ; Georgia Institute of Technology. Center for the Science and Technology of Advanced Materials and Interfaces ; Georgia Tech Polymer Network ; Case Western Reserve University
    Recently, numerous new synthetic approaches have been used to develop macromolecular materials that “self-assemble” into nano-scale morphologies. This lecture addresses another approach – the solventless “forced-assembly” of extrudable synthetic polymers down to the nano-scale. Numerous commercial films currently available, used primarily in food packaging, have only a few layers. These films have a desirable mix of end-use characteristics. Layer-multiplying devices permit polymers with dissimilar solid state structures and properties to be combined into unique microlayer and nanolayer systems with thousands of layers. Studies of these layered polymer composites down to the nano-scale have revealed unique properties which are only achievable when the layers are thin enough to produce synergistic combinations of key properties of the constituent components. Recently, a new highly flexible continuous process for creating unique nanofibers by a related solventless co-extrusion methodology will also be described with particular emphasis on membrane filters for gaseous and liquid separation systems.