Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session Y59: Soft Composites: Mechanics and Structure IIFocus
|
Hide Abstracts |
Sponsoring Units: GSOFT Chair: Moumita Das, Rochester Institute of Technology Room: BCEC 257B |
Friday, March 8, 2019 11:15AM - 11:51AM |
Y59.00001: Dynamics of interacting nanoparticles in complex polymeric solutions Invited Speaker: Jacinta Conrad The nanoscale mechanisms underlying the unusual mechanical properties of polymer nanocomposites and other soft composites remain elusive. Because nanoparticles are of comparable size to heterogeneities present in many complex fluids, their dynamics cannot be described through the framework of microrheology but rather decouple from the bulk fluid properties. Indeed, nanoparticles diffuse many orders of magnitude faster than expected when coupled to complex fluid relaxations on similar length scales, or much more slowly than expected when physically obstructed. Interactions between the nanoparticles, arising from high particle densities and/or chemical surface modifications, can further modify their dynamics. To understand the underlying physics of transport in this size regime, we measure the dynamics of nanoparticles and polymers in solution, which are simple models of polymer nanocomposites with well-controlled and tunable heterogeneities, using x-ray photon correlation spectroscopy and neutron spin-echo spectroscopy. Electrostatic charges lead to long-range interactions between the particles in organic solvents without disrupting the structure or dynamics of the surrounding polymer solution. The long-range interparticle interactions slow nanoparticle dynamics across the interparticle distance, even though the nanoparticle dynamics are subdiffusive and coupled to the polymer relaxations. Grafted polymers help to stabilize the nanoparticles in complex fluids and lead to soft physical interactions between the grafted particles and the surrounding polymer chains that alter their transport. Our work illustrates that the particle surface chemistry sensitively modifies the transport of nanoparticles through complex media. |
Friday, March 8, 2019 11:51AM - 12:03PM |
Y59.00002: Deformation in polymer nanoparticle composites (PNC) at ultra high loading: interplay of jammed solids and glassy mechanics Emily Lin, Robert Riggleman Polymer nanoparticle composites (PNC) with ultra high loading of nanoparticles (NP) (>50%) have been shown to exhibit simultaneously improved strength and stiffness without compromising, and sometimes even improving, the toughness compared to the neat systems. As a result, these composites have become an interesting class of material for a variety of applications. Furthermore, when the particle volume fraction approaches random-close-pack, these composite systems become a combination of a jammed solid (the random-close-packed NPs) filled with a glass-forming polymer in its interstices. In our study, we aim to understand the origin of these performance enhancements by examining the dynamics of both polymer and NPs during active deformation. We performed molecular dynamics simulation of coarse-grained, glass forming polymers equilibrated in the voids of a random-close-packed NP packing and subsequently applied uniaxial tensile strain to the bulk system. We examined the mechanical characteristics of the PNC systems with different polymer fill fractions at temperatures below the glass transition temperature. We also compared the NP rearrangement behavior in the presence of polymer to the neat NP systems to provide a molecular view of the toughening mechanism in these materials. |
Friday, March 8, 2019 12:03PM - 12:15PM |
Y59.00003: Visualization and Mechanical Study of a Transparent Filled Rubber Zach Gault, Zsolt Terdik, Joerg Werner, Frans A Spaepen, David A Weitz Filled rubbers are composite materials containing two interpenetrating phases: crosslinked elastomers, and a ‘filler’ consisting of colloidal particle aggregates. Above a critical volume fraction, the colloidal aggregates form a system-spanning subnetwork that reinforces the elastomer network and introduces a new energy loss mechanism at low strains of only 1-5%. This loss mechanism, known as the Payne Effect, is one of the mechanical hallmarks of filled rubbers and is a major contributor to rolling friction in tires. We create a transparent model filled rubber which exhibits the mechanical hallmarks of traditional filled rubbers, but can be optically imaged. Fluorescent silica nanoparticles provide optical contrast needed to distinguish the two phases. With this system we can directly observe microstructural changes of filler particle aggregates during in situ shear deformation. We complement these observations with bulk rheological tests to gain new insight into the microscopic deformations underlying the Payne effect. By controlling filler loading and crosslink density, we can tune the microstructure of our composite to better understand the relation between its structure and mechanical properties. |
Friday, March 8, 2019 12:15PM - 12:27PM |
Y59.00004: Mechanical response of composite biopolymer networks in the vitreous gel in our eyes Pancy Lwin, Scott Franklin, David Ross, George Thurston, Moumita Das The vitreous gel in the human eye is a viscoelastic composite network of stiff collagen fibers and softer hyaluronic acid (HA) polymers. Its material properties are critical to vitreous function, and ultimately to that of the eye, and depend on applied stresses, concentrations, and constituent filament stiffnesses. Although it has long been known to undergo dramatic changes with aging and disease, the key vitreous gel phase transitions and their mechanical consequences are not well understood. We mathematically model and investigate the mechanical response of the vitreous gel by modeling it as a composite network made of (i) a stiff network of collagen fibers, and (ii) a flexible polyelectrolyte network of HA. Our results relate the linear and nonlinear mechanical response of this composite network to the structure, micromechanics, and concentrations of the constituents, and may provide insights into mechanical changes associated with vitreous disorders. |
Friday, March 8, 2019 12:27PM - 12:39PM |
Y59.00005: In situ mechanical reinforcement of polymer hydrogels via metal-coordinated mineralization Niels Holten-Andersen Over millions of years, various types of organisms have evolved the ability to synthesize exceptionally strong and tough organic-inorganic composites through cell regulated in situ mineralization of macromolecular material scaffolds.1 Borrowing inspiration from such complex biomineral material processing, we have found that metal-coordinate polymer networks can be utilized as model macromolecular scaffolds for controlled in situ hydrogel mineralization. Starting with a monodisperse metal-coordinate polymer hydrogel network, we show that metal-ion coordination crosslinks can serve as nucleation sites for mineral growth, thereby allowing significant mechanical reinforcement upon limited mineralization of the polymer hydrogel scaffold. By targeting nanoscale mineral particle growth directly at the metal-coordinate network crosslink sites, we observe simultaneous significant increases in stiffness and magnetization of the resulting hydrogels with less than 0.1 % volume of minerals. We demonstrate that the method of controlling mineralization of polymer hydrogel networks through metal-coordination is general, and therefore potentially offers a broad platform for the development of new bio-inspired organic-inorganic composite materials processing systems. |
Friday, March 8, 2019 12:39PM - 12:51PM |
Y59.00006: Confocal Microrheology of biopolymer Hyaluronan Jared Welch, Scott Franklin, George Thurston, Moumita Das, David Ross Hyaluronan is a biopolymer that is found throughout the human body in connective tissue. To investigate the viscoelastic properties of this material the diffusion of carboxylate spheres in buffered solutions containing varying concentrations of 60 kDa Hyaluronan was monitored using a confocal microscope. The solutions contained a mix of D2O/H2O to match the density of the spheres. The trajectories of the spheres were analyzed using one- and two-point microrheology analysis methods. At low concentrations of hyaluronan the dynamic viscosity was extracted using the Stokes-Einstein relation. We compare these viscosities with theoretical models and use them to estimate the overlap concentration. At high concentrations, the spheres move in a way that does not correspond to normal diffusion, and the mean-squared displacement vs. lag time displays an interesting concentration-dependent inflection point. We compare results from one- and two-point particle tracking analysis. |
Friday, March 8, 2019 12:51PM - 1:03PM |
Y59.00007: A continuum model of the viscoelastic response of the vitreous gel Logan Melican, Scott Franklin, George Thurston, David Ross, Moumita Das The vitreous gel is a transparent, hydrated extracellular matrix filling the posterior cavity of the eye behind the lens and is surrounded by and attached to the retina. More specifically it is a composite material primarily made of a dilute network of stiff collagen fibrils and flexible polysaccharide (Hyaluronic Acid) chains within an aqueous solution. It has complex viscoelastic properties but becomes progressively fluid-like with age, leading to a number of pathologies. Here we develop a continuum mathematical model of the vitreous gel by drawing from two-fluid models of semi dilute polymer solutions. We solve a system of coupled partial differential equations for the soft and flexible networks, and the fluid via a combination of spectral and Runge-Kutta methods, and obtain the frequency dependent viscoelastic properties of the system as a function of polymer stiffness and density, and fluid viscosity. Our results will help to better understand rheological experiments on the vitreous, and provide new insights into the origin of vitreous liquefaction. |
Friday, March 8, 2019 1:03PM - 1:15PM |
Y59.00008: Optical tweezers microrheology reveals the viscoelastic properties of entangled ring-linear DNA blends Karthik Reddy Peddireddy, Megan Lee, Rae Robertson-Anderson Solutions of entangled polymers display complex and intriguing viscoelastic properties that are still poorly understood. While the reptation model can describe the viscoelastic properties of entangled melts of linear polymers, the model is ill-equipped to deal with circular or ring polymers, blends of polymers of varying topologies, or solutions of polymers at concentrations near the critical entanglement concentration. DNA is an excellent model system for resolving this issue as it occurs naturally in linear and circular forms. Here, we use optical tweezers microrheology to measure the linear and nonlinear viscoelastic response of semidilute and entangled blends of circular and linear DNA. We characterize the dependence of viscoelastic properties on the ratio of circular and linear chains in the blend as well as the overall solution concentration. Our results show intriguing properties of blends compared to single-component systems including increased stiffness coupled with faster relaxation rates. |
Friday, March 8, 2019 1:15PM - 1:27PM |
Y59.00009: Phase behavior and morphology of multicomponent mixtures Sheng Mao, Derek Kuldinow, Mikko Haataja, Andrej Kosmrlj Multicomponent systems are ubiquitous in nature and industry. While the physics of binary and ternary liquid mixtures is well-understood, the thermodynamic and kinetic properties of N-component mixtures (N>3) have remained relatively unexplored. Inspired by recent examples of intracellular phase separation, we investigate equilibrium phase behavior and morphology of N-component mixtures within the Flory-Huggins theory of regular solutions. In order to determine the number of coexisting phases and their compositions, we developed a new algorithm to construct complete phase diagrams, based on numerical convexification of the discretized free energy. Together with a Cahn-Hilliard approach for kinetics, we employ this method to study mixtures with N=4 and 5. We report on both the coarsening behavior of such systems and the resulting morphologies in 3D. The number of coexisting phases and their compositions can also be extracted with Principal Component Analysis (PCA) and K-Means algorithms. Finally, we discuss how to reverse engineer the interaction parameters and volume fractions of components in order to achieve a range of desired packing structures, such as nested "Russian dolls" and encapsulated Janus droplets. |
Friday, March 8, 2019 1:27PM - 1:39PM |
Y59.00010: Anisotropic self-assembly of polarizable colloidal mixtures Ziwei Wang, Erik Luijten Particles with directional interactions represent promising building blocks for new functional materials and are often realized by particles with anisotropic shape or with patchy directional bonds. Here we demonstrate that binary suspensions of oppositely charged size-asymmetric colloids robustly self-assemble into a variety of anisotropic superstructures, resulting from the many-body dielectric effects which impart effective directionality to the inter-particle interactions. Via simulations, we illustrate how both local coordination number (connectivity) and fractal dimension can be well controlled through variation of the size ratio and the mismatch in relative permittivity. The mechanism we have identified offers a potential avenue to designing materials with controllable structural properties. |
Friday, March 8, 2019 1:39PM - 1:51PM |
Y59.00011: Beyond Bi-disperse: A study of propensity in a Kob-Andersen Quartet Cordell Donofrio, Eric Weeks We simulate the Kob-Andersen bidisperse glassformer system to study dynamics near the glass transition. As the name implies, the standard KA system is composed of two different sized particles. In our system we split the population of large particles into its own binary where half are increased in size and the other half decreased by the same (small) percentage. A similar binary is created for the small particles. Isoconfigurational ensemble runs are then made to understand the influence of slight “errors” in particle size. An isoconfigurational ensemble is a series of simulations, each with the same starting positions but with randomized velocities consistent with the temperature (following Widmer-Cooper et al, 2004). The “propensity” of each particle is defined as the average motion of that particle, averaged over this ensemble. While normally this is done with the exact same particles in the starting positions, having multiple variants of each particle size allows for slight changes to be made to the structure at the start of each run in the isoconfigurational ensemble. We seek to find how large of a change in structure is needed to remove propensity from the system. |
Friday, March 8, 2019 1:51PM - 2:03PM |
Y59.00012: Plant Inspired Soft Material Composite with Liquid Encapsulations Amrita Kataruka, Shelby Hutchens Plants are unique mechanical structures that combine high water content with structural elements. Unlike common soft material and liquid composites (ex: hydrogel), plants compartmentalize their water using semi-permeable membranes. We synthesize plant tissue analogs, idealized as closely packed water droplets surrounded by thin walls of PDMS, to understand their mechanical response. The analogs are created by high internal phase emulsion templating. We choose PDMS because it is highly stretchable and semipermeable yet does not swell in water. It also has a tunable modulus that allows us to capture the varied range of stiffness in flora. However, due to the high viscosity of PDMS prepolymer, adding large quantities of water to the emulsion demands very high shear force. Using microfluidics is also difficult because high pressure – required to make PDMS flow through the channels – easily ruptures device assembly. To overcome these challenges, we combine shear-mixing with centrifugation. The influence of viscosity ratio, amount of stabilizer, and fabrication specifics on droplet generation and structure are investigated. We find that with careful manipulation of the above governing parameters, the micromorphology of the composite can be designed to within plant-cell relevant ranges. |
Friday, March 8, 2019 2:03PM - 2:15PM |
Y59.00013: Programming shape changes in tri-stable bilayer structure Shicheng Huang, Lin Wang, Dong Wang, Xing Guo, Guangchao Wan, Jing Fan, Zi Chen The programmable shape transition in response to external stimuli has attracted increasing attention. Multi-stable structures represent a stimuli-responsive structure that features more than one stable shape and transition from one to another, appropriate for applications such as in micro-robotics. Although bi-stable structures have been extensively investigated, very few studies have been focusing on tri-stability of such structures. Here we design a partially bonded bilayer structure composed of a SMP layer and a rubber strip. When subjected to changes in temperature, this structure exhibits tri-stability and transits between hemihelical, left-handed and right handed-helical shapes. Theoretical analysis, experiments, and finite element simulations are conducted to identify the mechanism of the tri-stability and used to predict the deformed configuration given geometric and material parameters. Our work provides a facile strategy for fabricating smart reconfigurable structures for a broad range of applications in intelligent materials. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700