Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session R30: Physics of Bio-Inspired MaterialsFocus
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Sponsoring Units: GSOFT DBIO Chair: Kyoo-Chul (Ken) Park, Northwestern University Room: BCEC 162B |
Thursday, March 7, 2019 8:00AM - 8:36AM |
R30.00001: Mechanically Guided Assembly of Bio-Inspired 3D Mesoscale Frameworks Invited Speaker: John Rogers
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Thursday, March 7, 2019 8:36AM - 8:48AM |
R30.00002: Spatial control of frost formation on hydrophobic surfaces with millimetric serrated features Yuehan Yao, Emma Feldman, Kyoo-Chul (Ken) Park Numerous studies have focused on a low surface energy coating and a micro/nanoscale surface texture to design functional surfaces that delay frost formation and reduce ice adhesion. However, the scientific challenges for long-term icephobic surfaces have not been fully addressed because of degradation such as mechanical wearing. Inspired by the suppressed frost formation on concave regions of natural leaves, here we report findings on the frosting process on hydrophobic surfaces with various serrated structures. Dropwise condensation, the first stage of frosting, is enhanced on the peaks and suppressed in the valleys when the wavy surface is exposed to humid air, causing frosting to initiate from the peak. The condensed droplets in the valley are then evaporated, resulting in a non-frost band. The effects of surface topography on the frost pattern are systematically studied by varying the serrated geometry defined as the vertex angle, and numerically modeling the spatial distribution of diffusion flux of water vapor on the wavy surface. Under different ambient humidity levels, the magnitudes of diffusion flux at the non-frost boundaries of the surfaces are nearly identical, implying that the critical value of diffusion flux is the key to understand the non-frost pattern. |
Thursday, March 7, 2019 8:48AM - 9:00AM |
R30.00003: Understanding Nanostructured Topography on Flower Petals: Hierarchical Wrinkles in Soft Multilayers Chao Chen, Alfred Crosby Hierarchical wrinkles on flower petals enable unique iridescence to attract pollinators. Although similar patterns have been observed on graded elastomers, mimesis of the natural patterns and relative dimensions with a controllable and tunable manner is challenging. Inspired by the multiple-layered structure of petal skins, here we present a physical model and a corresponding numerical model based on three-layered thin films. The layer-by-layer integration provides accuracy in controlling thickness and mechanical properties of thin films, thus enabling quantitative relations between physical and numerical models. We quantify the sequential development of a hierarchical structure, consisting of small wrinkles coupled with larger sinusoidal deformations. We found their wavelength follows the bilayer wrinkling theory; whereas the amplitudes of small wrinkles have a systematic spatial distribution largely controlled by larger wrinkles. We also discovered a collapse from the dual-wrinkling mode to a single-wrinkling mode, which depends upon thickness and mechanical properties of top layers. A phase map of the two wrinkling modes is constructed to guide the design of hierarchical wrinkles. |
Thursday, March 7, 2019 9:00AM - 9:12AM |
R30.00004: Mechanics of Elephant Trunk Wrinkles Andrew Schulz, David L Hu Elephant skin is obviously wrinkled, but no quantitative measurements have been made of why the trunk has such wrinkly skin. Through videos of trunk movement at Zoo Atlanta and dissections of a trunk from the Smithsonian Institute we report the geometry of the wrinkles and rationalize their function. Elephants can elongate their trunk by over 40%, but have little or no compression capability. Skin at the trunk’s root forms square-waved wrinkles and is twice as thick as the skin at the tip which forms sinusoidal wrinkles. We rationalize that elephants use these wrinkling properties to perform incredible bending, elongation, and strength with their trunk. The energy of wrinkling will be compared to wrinkling phenomenon in the biological world. This work will relate to biologically inspired soft robotic manipulators. |
Thursday, March 7, 2019 9:12AM - 9:24AM |
R30.00005: Bioinspired materials with self-regulating mechanical properties upon loading/damages Santiago Orrego, Zhezhi Chen, Deching Hou, Urszula Krekora, Sung Kang Nature produces outstanding materials for structural applications such as bones and coral reefs that can adapt to their surrounding environment and repair damages. This leads to the formation of mechanically efficient structures for optimal biomechanical and energy-efficient performance and long-term durability. However, it has been a challenge for synthetic materials to change and adapt their structures and properties to address the changes of loading conditions or damages. To address the challenge, we report a bioinspired material system that triggers mineral synthesis from ionic solutions on organic scaffolds upon mechanical loadings and/or damages so that it can self-adapt to mechanical loadings and regenerate upon damages. The mechanism also allows the formation of functionally graded materials using a simple one step process. We envision that our findings can open new strategies for making synthetic materials with self-regulating mechanical properties. |
Thursday, March 7, 2019 9:24AM - 9:36AM |
R30.00006: Fog collection on wire arrays Youhua Jiang, Christian Machado, Shaan Savarirayan, Kyoo-Chul (Ken) Park The upright, wire-like leaves of Stipagrostis sabulicola, a grass species in the Namib Desert, shows excellent fog collection performance. Inspired by such wire geometry, we aim to understand the mechanism of fog collection on individual vertical wires and multiple-wire arrays. We visualized how fog droplets are collected on a wire and measured the resulting fog-collection rate while varying wire diameter, surface wettability, and wind speed. Results show that fog-collection rates on a single wire are determined by deposition efficiency, an aerodynamics-related parameter. Surface wettability has a negligible effect on the fog collection rate at low wind speeds (e.g., 0.5 m/s). By contrast, there appears to be a strong effect of wettability at high wind speeds (e.g., 3 m/s), where surfaces with the lowest droplet adhesion performs worst. Such phenomenon is explained by the competition between the air drag force and the droplet retention force on a surface, both of which are determined by surface wettability and wire diameter. Building on the knowledge gained from individual wires, we optimize the design of multiple-wire arrays, which shows a four-fold enhancement in fog-collection rate compared to a single wire of the same surface area. |
Thursday, March 7, 2019 9:36AM - 9:48AM |
R30.00007: Siderophore Inspired Molecules to Mediate Collagen Thin Film Adhesion Roberto Andresen Eguiluz, George Degen, Eric Valois, Garrett Lindsey, Kai Kristiansen Adhesion in biological environments (aqueous ionic solutions) is challenged by the high dielectric constant of water which reduces van der Waals interactions, ions in solution which screen electrostatic interactions, and the hydration layers both on hydrophilic substrates and surface-bound ions which discourage adhesive contact between glues and the substrate. In this study, we investigated adhesion between symmetric thin films of collagen type-1 (Col-1), a major component of the extracellular matrix (ECM), mediated by synthetic analogs of siderophores (small molecule bacterial iron chelators). |
Thursday, March 7, 2019 9:48AM - 10:00AM |
R30.00008: Surface segregation of binary particles in photonic colloidal assemblies Ming Xiao, Ziying Hu, Thomas Gartner, Xiaozhou Yang, Weiyao Li, Arthi Jayaraman, Nathan C. Gianneschi, Matthew D. Shawkey, Ali N Dhinojwala A simple one-pot emulsion-based process offers unique advantages in controlling assembly of particles with applications in producing structural colors, self-stratifying coatings, and capsules for drug delivery. Here, we combine experiments and molecular dynamics simulations to demonstrate the importance of chemistry, density, and size of particles in controlling the surface segregation in photonic colloidal assemblies from a binary mixture of melanin and silica particles. Surface segregation also influences the structural colors of these supraballs. In addition, melanin is a multifunctional biological pigment and the control of its segregation at supraball surface leads to novel ways to modulate unique surface properties of colloidal assemblies. |
Thursday, March 7, 2019 10:00AM - 10:12AM |
R30.00009: The prediction and design of bio-inspired structural colors using colloidal glasses Victoria Hwang, Anna B Stephenson, Solomon Barkley, Vinothan N Manoharan Many species of birds display structural colors that arise from the constructive interference of light that is scattered from the internal structure of the feathers. In blue Cotinga birds, the colors are independent of the angle between light source and observer owing to the glassy arrangement of air spheres in keratin in the feather barb (E. R. Dufresne et al, Soft Matter, 2009, 5, 1792-1795). Such colors can be mimicked in colloidal glasses, but while the locations of the peaks in reflectance spectra are accurately predicted by single-scattering models, weak multiple scattering also contributes to the reflected intensity. We develop a model that quantitatively predicts the reflectance spectra of colloidal glasses. To model the multiple scattering, we use a Monte Carlo approach to simulate photon trajectories. We find good agreement between experimental reflectance spectra and the model. We also develop an optimization algorithm to find the parameters required to make specific colors and explore the range of hues that can be achieved with colloidal glasses. |
Thursday, March 7, 2019 10:12AM - 10:24AM |
R30.00010: The physical origin of the reflectance features of structurally-colored colloidal glasses Anna B Stephenson, Victoria Hwang, Solomon Barkley, Vinothan N Manoharan We use colloidal glasses as a model system to study the physics in structurally-colored systems in nature, such as the blue feather barbs of the plum-throated Cotinga. Both are composed of spheres in an arrangement with short-range order and long-range disorder, and in both cases the color results from interference rather than absorption. Unlike biological systems, however, colloidal glasses can be fabricated in the lab, and we can tune their reflectance spectra. While the location of the primary structural resonance in their spectra can be predicted using a single-scattering theory, other features of the spectra, such as the increase in reflection at short wavelengths, cannot be explained by single scattering alone. To understand the effect of multiple scattering on the color, we do co- and cross-polarized measurements of the reflection spectra, and we interpret these measurements using Monte Carlo simulations of photons scattering inside the disordered structure. |
Thursday, March 7, 2019 10:24AM - 10:36AM |
R30.00011: Learning from butterflies: Folding lipid membranes to build photonic-crystal materials Simon Merminod, Huang Fang, William B Rogers In some butterfly wing scales, a cellular membrane is folded into a periodic nanostructure which generates color and iridescence by constructive interference of visible light. Inspired by this biological achievement, where protein binding is thought to mediate the energetics and dynamics of membrane folding, we aim to build photonic-crystal materials from self-assembly of small particles on artificial membranes. We start by characterizing the interactions between colloidal particles and a supported phospholipid membrane. We graft single-stranded DNA onto them, so that hybridization of complementary strands generates a specific, attractive force between the particles and the membrane. Using a total internal reflection microscope, we measure interactions with femtonewton resolution and kilohertz dynamics. We find that ligand-receptor affinity dramatically affects the energetics and dynamics of particle-membrane interactions: over a temperature range of a few degrees Celsius, adhesion strength varies by about 10 kT, while bound lifetimes and particle mobility change by orders of magnitude. These results may lead to better understanding of self-assembly of particles on fluid membranes, and ultimately enable self-assembling, membrane-based materials with remarkable optical properties. |
Thursday, March 7, 2019 10:36AM - 10:48AM |
R30.00012: Self-assembly of protein-made structures Agnese Curatolo, Carl Goodrich, Ofer Kimchi, Michael Phillip Brenner, Scott Boyken, Zibo Chen, Yang Hsia, David Baker Living organisms create complex protein-based materials with remarkable properties. Inspired by those, one could ask if it would be possible to design protein-based materials from scratch for specific human uses, with applications ranging from medicine to biomaterials. |
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