Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session C49: Reinforced (By) WaterInvited
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Sponsoring Units: GSOFT DPOLY Chair: Ahmed Elbanna, Yuhang Hu, University of Illinois, Urbana-Champaigne Room: 396 |
Monday, March 13, 2017 2:30PM - 3:06PM |
C49.00001: Mechanical behavior of hydrogels Invited Speaker: Zhigang Suo Several recent findings show that hydrogels can achieve properties and applications well beyond previously imagined. Most existing hydrogels, like Jell-O and tofu, are fragile and dry out in open air. We have made hydrogels as tough as rubber, and retain water in low-humidity environment. We have used hydrogels to develop devices to mimic the function of axons, nerves, and skins. They are highly stretchable and transparent. This talk describes the mechanical behavior of hydrogels. Emphasis will be given to recent work on adhesion, fatigue resistance, and flaw tolerance. [Preview Abstract] |
Monday, March 13, 2017 3:06PM - 3:42PM |
C49.00002: Multi-scale Multi-mechanism Toughening of Hydrogels Invited Speaker: Xuanhe Zhao Hydrogels are widely used as scaffolds for tissue engineering, vehicles for drug delivery, actuators for optics and fluidics, and model extracellular matrices for biological studies. The scope of hydrogel applications, however, is often severely limited by their mechanical properties. Inspired by the mechanics and hierarchical structures of tough biological tissues, we propose that a general principle for the design of tough hydrogels is to implement two mechanisms for dissipating mechanical energy and maintaining high elasticity in hydrogels. A particularly promising strategy for the design is to integrate multiple pairs of mechanisms across multiple length scales into a hydrogel. We develop a multiscale theoretical framework to quantitatively guide the design of tough hydrogels. On the network level, we have developed micro-physical models to characterize the evolution of polymer networks under deformation. On the continuum level, we have implemented constitutive laws formulated from the network-level models into a coupled cohesive-zone and Mullins-effect model to quantitatively predict crack propagation and fracture toughness of hydrogels. Guided by the design principle and quantitative model, we will demonstrate a set of new hydrogels, based on diverse types of polymers, yet can achieve extremely high toughness superior to their natural counterparts such as cartilages. [Preview Abstract] |
Monday, March 13, 2017 3:42PM - 4:18PM |
C49.00003: Shape morphing and motion of responsive hydrogel composites Invited Speaker: Ryan Hayward Composites of stimuli-responsive hydrogels paired with stiff structural elements or functional inorganic materials offer myriad opportunities to control the shape, properties, and motion of materials. In one example, our group has studied the geometry and mechanics of swelling-induced buckling of polymer trilayer films consisting of patterning rigid layers sandwiching a swellable hydrogel layer. Of particular recent interest has been the formation of helical structures from ‘seedpod’-type architectures with perpendicular orientation of stripes on opposite faces. We have studied the concatenation of two or more helical segments, yielding simple geometric design rules for the fabrication of 3D constructs. In a second example, we have considered the light-driven reshaping and motion of hydrogels containing plasmonic nanoparticles as photothermal heating elements. In contrast to systems pre-programmed to take on a single, or perhaps a few, different 3D shapes, this approach enables continuous shape reconfiguration, and correspondingly, directed motion of composite hydrogel sheets. [Preview Abstract] |
Monday, March 13, 2017 4:18PM - 4:54PM |
C49.00004: Hygroscopic Metamorphic 4D Pleats Invited Speaker: Shu Yang There have been significant interests in morphing 2D sheets into 3D structures via programmed out-of-plane distortion, including bending, tilting, rotating, and folding as seen in recent \textit{origami} and \textit{kirigami} strategies. Hydrogel is one of the unique soft materials that can swell and shrink, thereby enabling real-time 4D motions in response to external stimuli, such as pH, temperature, and moisture. To achieve reliable folding behaviors, it often requires a large amount of water molecules or ions diffusing in and out of the hydrogel sheet, thus the entire sheet is immersed in an aqueous solution. Here, we demonstrate the design and folding of hierarchical pleats patterned from a combination of hydrophobic and hygroscopic materials, allowing us to spatially and locally control the water condensation induced by environmental humidity. In turn, we show out-of-plane deformation of the 2D sheets only in the patterned hygroscopic regions, much like the folding behaviors of many plants. By designing the dimension, geometry, and density of hygroscopic microstructures (as pixels) in the hydrophobic materials, we can display the enhanced water condensation together with the spatial guidance of obtained droplets as unified water-harvesting systems. When the water droplets become large enough, they roll off from the hierarchical sheet along the inclined plane that is programmed by the hygroscopic motion of hydrogel, and eventually wrapped by the folded sheet to keep them from evaporation. [Preview Abstract] |
Monday, March 13, 2017 4:54PM - 5:30PM |
C49.00005: The Unusual Mechanics of Gel-Liquid Composites Invited Speaker: Robert Style |
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