Soft Matter Incubator
Soft Matter Incubator
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ItemMechanics of Active Networks – Lessons from Fire Ant Aggregations(Georgia Institute of Technology, 2018-04-19) Sridhar, Shankar Lalitha ; Vernerey, Franck ; Fernandez-Nieves, Alberto ; Shen, Tong ; Soft Matter Incubator ; Center for the Science and Technology of Advanced Materials and Interfaces ; University of Colorado BoulderBiological assemblies in nature are seen as active matter due to their ability to perform intelligent collective motion based on neighbor interactions and sometimes without any centralized control or leadership. Fire ants are a great example in this context and display a rich class of material behaviors, including elasticity, viscous flow, and self-healing. Although classical theories in mechanics have enabled us to mechanically characterize this system, there is still a gap in our understanding on how individual ant behavior affects the emerging response of the aggregation. I will discuss an alternative approach from a statistical perspective where the population distribution of ants evolves due to mechanical deformation, and individual ant’s leg detachment and attachment events. Numerical simulations of the aggregation’s response in diverse situations, such as jamming (density) and shear thinning (reduced viscosity) will be presented and compared to experimental measurements.
ItemUnusual Director Configurations and Diffusion Driven by Liquid Crystal Elastic Anisotropy(Georgia Institute of Technology, 2018-04-18) Yodh, Arjun G. ; Soft Matter Incubator ; Center for the Science and Technology of Advanced Materials and InterfacesI will describe experiments that probe effects of twist elastic anisotropy in lyotropic chromonic liquid crystals (LCLCs) on the director configurations in cylinders/spheres and on particle diffusion. Time permitting, I will also describe measurements of LCLC “coffee rings” and of twist fluctuations in suspended spherical LC droplets.
ItemWhy is Structural Hierarchy So Prevalent in Biological Materials?(Georgia Institute of Technology, 2018-04-19) Michel, Jonathan ; Yunker, Peter J. ; Soft Matter Incubator ; Center for the Science and Technology of Advanced Materials and InterfacesStructural 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.
ItemLocal and Global Avalanches in Sheared Granular Materials(Georgia Institute of Technology, 2018-04-20) Zadeh, Aghil Abed ; Barés, Jonathan ; Behringer, Robert ; Soft Matter Incubator ; Center for the Science and Technology of Advanced Materials and InterfacesWe 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.
ItemSelf–Assembled DNA Liquids: Properties and Protein Activation(Georgia Institute of Technology, 2018-04-19) Saleh, Omar ; Soft Matter Incubator ; Center for the Science and Technology of Advanced Materials and InterfacesBiomolecules 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.
ItemHow Hidden Geometric Symmetries in Origami Generate New Folding Mechanisms(Georgia Institute of Technology, 2018-04-19) McInerney, James ; Rocklin, D. Zeb ; Soft Matter Incubator ; Center for the Science and Technology of Advanced Materials and InterfacesThe 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.
ItemHighly Efficient Oil-Water Separation Using Surface-Programmable Membranes(Georgia Institute of Technology, 2018-04-20) Zeng, Minxiang (Glenn) ; Zhang, Eric ; Huang, Dali ; Cheng, Zhengdong ; Soft Matter Incubator ; Center for the Science and Technology of Advanced Materials and InterfacesThe 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.
ItemThe Topological Character of Smectics(Georgia Institute of Technology, 2018-04-18) Kamien, Randy ; Soft Matter Incubator ; Center for the Science and Technology of Advanced Materials and InterfacesThough 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.
ItemGeometric Underpinnings of Auxetic Behavior(Georgia Institute of Technology, 2018-04-18) Streinu, Ileana ; Soft Matter Incubator ; Center for the Science and Technology of Advanced Materials and InterfacesIn materials science, auxetic behavior is characterized by negative Poisson's ratios. We have recently developed a purely geometric theory of auxetic behavior for periodic framework materials. In this talk I will present the main ideas (rooted in rigidity theory) as well as the algorithmic consequences, which lead to efficient methods for detecting the local (infinitesimal) behavior. The design of novel two dimensional auxetic structures is facilitated by our theory of expansive mechanisms, fully characterized as periodic pseudo-triangulations. I will conclude with some recent results for designing three dimensional auxetic structures. Joint work with Ciprian Borcea, Rider University.
ItemNew Results for Old Physics: Critical Phenomena for Colloids in Microgravity(Georgia Institute of Technology, 2018-04-19) Weitz, Dave ; Soft Matter Incubator ; Center for the Science and Technology of Advanced Materials and InterfacesThis 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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