Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session W25: Focus Session: Cooperative Phenomena in Plasticity III |
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Sponsoring Units: DMP Chair: Robert Maass, University of Gottingen Room: 203B |
Thursday, March 5, 2015 2:30PM - 2:42PM |
W25.00001: ABSTRACT MOVED TO F23.00009 |
Thursday, March 5, 2015 2:42PM - 2:54PM |
W25.00002: Dsign of Inorganic Electrides Zhang Yunwei, Peng Feng, Ma Yanming Electrides, in which all of or part of the valence electrons occupy interstitial regions in the crystal and behave as anions, have been synthesized at ambient or high-pressure conditions [1]. Their loosely bound anionic electrons make electrides good candidates for electro-active materials. Here, we report a developed methodology to systematically design electrides for given chemical systems. The new approach is based on the swarm-intelligence CALYPSO algorithm on structure prediction [2-3] and requires only the chemical compositions to predict the electride phases. In contrast to the traditional ground state structure prediction method where the total energy was solely used as the fitness function, we adopted a new fitness function in combination with the first-principles calculation to select the optimal solutions for a description of given chemical systems. The result suggested that our approach is reliable and can be widely applied into design of new electrides. \\[4pt] [1] Ma, Y. et al. Transparent dense sodium. Nature 485, 182-185 (2009).\\[0pt] [2] Wang, Y., Lv, J., Zhu, L. {\&} Ma, Y. Crystal structure prediction via particle-swarm optimization. Phys. Rev. B 82, 094116 (2010). [Preview Abstract] |
Thursday, March 5, 2015 2:54PM - 3:06PM |
W25.00003: Spontaneous thermally-induced delamination of polymer films Punit Kohli, Kexin Jiao, Chuanhong Zhou, Jared Wynne, Anish Poude, Philip Chu In this talk, we will discuss spontaneous thermally-induced biaxial delamination of thin polymer films from flat surfaces. The delamination results in the formation of ultra-high aspect ratio (up to 1000) of micro-ribbons of polydimethylsiloxane. The thickness, width, and length of the micro-ribbons is about 10 $\mu $m, 100 $\mu $m, and up to many centimeter respectively. We will demonstrate that the formation of polymer micro-ribbons can be experimentally controlled. Specifically, the thickness and mechanical properties of polymer, and geometrical and physical properties of the substrate played crucial roles in defining the delamination process. From the practical viewpoint, we demonstrate the use of the micro-ribbons for imaging and separation applications. [Preview Abstract] |
Thursday, March 5, 2015 3:06PM - 3:42PM |
W25.00004: Mechanical properties of 3D ceramic nanolattices Invited Speaker: Lucas Meza Developments in advanced nanoscale fabrication techniques have allowed for the creation of 3-dimensional hierarchical structural meta-materials that can be designed with arbitrary geometry. These structures can be made on length scales spanning multiple orders of magnitude, from tens of nanometers to hundreds of microns. The smallest features are controllable on length scales where materials have been shown to exhibit size effects in their mechanical properties. Combining novel nanoscale mechanical properties with a 3-dimensional architecture enables the creation of new classes of materials with tunable and unprecedented mechanical properties. We present the fabrication and mechanical deformation of hollow tube alumina nanolattices that were fabricated using two-photon lithography direct laser writing (DLW), atomic layer deposition (ALD), and oxygen plasma etching. Nanolattices were designed in a number of different geometries including octet-truss, octahedron, and 3D Kagome. Additionally, a number of structural parameters were varied including tube wall thickness ($t)$, tube major axis ($a)$, and unit cell size ($L)$. The resulting nanolattices had a range of densities from $\rho =$ 4 to 250 mg/cm$^{3}$. Uniaxial compression and cyclic loading tests were performed on the nanolattices to obtain the yield strength and modulus. In these tests, a marked change in the deformation response was observed when the wall thickness was reduced below 20nm; thick-walled nanolattices ($t$\textgreater 20nm) underwent catastrophic, brittle failure, which transitioned to a gradual, ductile-like deformation as wall thickness was reduced. Thick-walled nanolattices also exhibited no recovery after compression, while thin-walled structures demonstrated notable recovery, with some recovering by 98{\%} after compression to 50{\%} strain and by 80{\%} when compressed to 90{\%} strain. Across all geometries, unit cell sizes, and wall thicknesses, we found a consistent power law relation between strength and modulus with relative density of $E \propto \rho^{\, 1.6}$ and $\sigma_{y} \propto \rho ^{\, 1.75}$. This scaling marks an improvement over other lightweight and ultralight materials, which normally scale as $E \propto \rho^{\, 2}$ or $E \propto \rho^{\, 3}$, but does not meet the analytic upper bound of a linear scaling with relative density that is predicted for stretching dominated geometries like the octet-truss. [Preview Abstract] |
Thursday, March 5, 2015 3:42PM - 3:54PM |
W25.00005: ABSTRACT WITHDRAWN |
Thursday, March 5, 2015 3:54PM - 4:06PM |
W25.00006: Shock induced chemistry in granular Ni/Al nanocomposites Mathew Cherukara, Timothy Germann, Edward Kober, Alejandro Strachan Intermolecular reactive composites find diverse applications in defense, microelectronics and medicine, where strong, localized sources of heat are required. However, fundamental questions of the initiation and propagation mechanisms on the nanoscale remain to be addressed, which is a roadblock to their widespread application. Motivated by experimental work which has shown that high-energy ball milling can significantly improve the reactivity as well as the ease of ignition of Ni/Al inter-metallic composites, we present large scale ($\sim$ 41 million atom) molecular dynamics simulations of shock-induced chemistry in granular Ni/Al nano-composites, which are designed to capture the microstructure that is obtained post milling. Shock propagation in these granular composites is observed to be extremely diffuse at low piston velocities, leading to a large inhomogeneity in the local stress states of the material. At higher piston velocities, the shock front is more homogeneous as a consequence of a change in the compaction mechanism; from plastic deformation mediated pore collapse at low piston velocities, to fluid filling of the pores at higher impact velocities. The flow of molten ejecta into the pores subsequently leads to the formation of vortices, where the reaction progresses much faster than in the bulk. [Preview Abstract] |
Thursday, March 5, 2015 4:06PM - 4:18PM |
W25.00007: Stoichiometric Control of DNA-Grafted Colloid Self-Assembly Thi Vo, Venkat Venkatasubramanian, Sanat Kumar, Babji Srinivasan, Suchetan Pal, Yugang Zhang, Oleg Gang There have been recent surges of interest in understanding the self-assembly of DNA-grafted colloids into different crystallographic lattices, namely CsCl, AlB$_{\mathrm{2}}$, Cr$_{\mathrm{3}}$Si, and Cs$_{\mathrm{6}}$C$_{\mathrm{60}}$. Conventional approaches view the number of grafted linkers and effective size of each colloid as the major governing design parameters. It is generally assumed that the mixed stoichiometries need to match those defined by the target structures in order to obtain the desired lattice. Thus, contributions from stoichiometry are considered secondary and its exact effects on lattice formation remains an open question. Theoretical extensions to the popular complementary contact model show that the equilibrium lattice structure can be tuned through direct control of stoichiometry. Our results are also validated through experimental observations of the equilibrium crystal morphologies at differing stoichiometric ratios. These findings strongly suggest that stoichiometry is a new handle that can be used to control DNA-grafted colloidal self-assembly. [Preview Abstract] |
Thursday, March 5, 2015 4:18PM - 4:30PM |
W25.00008: Computational Study of Nanoparticle Clustering via DNA Hyperdyzation Xu Ma, Mark J. Bowick, Rastko Sknepnek We use molecular dynamics simulation to study the self-assembly of small clusters through DNA hybridization in a binary mixture of spherical nucleic acid gold nanoparticles(SNA-GNPs) system. The resultant structures are self-assembled clusters with a varying number of large SNA-GNPs clusters around the small ones, forming dimers, trimmers, tetramers etc. The outcome structures can be tuned by adjusting external factors including temperature, particle hydrodynamics size ratio. [Preview Abstract] |
Thursday, March 5, 2015 4:30PM - 4:42PM |
W25.00009: Tetrahedrally bonded carbonates and aqueous carbonate anions under extreme conditions Ding Pan, Giulia Galli The carbonate ion, CO$_3^{2-}$, has a trigonal planar structure composed of carbon bonded with three oxygen atoms. The existence of tetrahedrally bonded carbonate units, CO$_4$, analogous to SiO$_4$ in silicates, has long been under debate. Using a combination of first-principles calculations and in situ infrared spectroscopy measurements [1], we provided definitive evidence that in magnesite, at pressures above 80 GPa, sp$^2$ bonded CO$_3$ trigonal groups transforms into sp$^3$ bonded CO$_4$ tetrahedral units. These units were found to be asymmetric, with two longer and two shorter C-O bonds. In addition, using first principles molecular dynamics we investigated carbonate anions in water at high temperature and pressure, corresponding to Earth's upper mantle conditions. We found significant quantities of bicarbonate ions dissolved in the liquid. The relevance of our simulation results for geophysical models of hydrous carbonates in the Earth will be discussed.\\[4pt] [1] Our work, Nat. Comm. 2014 (submitted). [Preview Abstract] |
Thursday, March 5, 2015 4:42PM - 4:54PM |
W25.00010: ABSTRACT MOVED TO S23.00008 |
Thursday, March 5, 2015 4:54PM - 5:06PM |
W25.00011: Fluorescent probes for shock compression spectroscopy Alexandr Banishev, James Christensen, Dana Dlott We have demonstrated the capability of using Rhodamine 6G dye as an ultrafast emission probe in high-speed shock compression of condensed matter. The ultimate time response of the probe, which functions as a high-speed pressure sensor, is limited by fundamental photophysical processes such as radiative rates, internal conversion rates and intersystem crossing rates. The time response has been greatly improved by encapsulating the dye in silica nano or microparticles. This probe was used to observed nanosecond viscoelastic shock compression of a polymer (PMMA), and has been used to monitor the response of individual grains of sand to high-speed impact. [Preview Abstract] |
Thursday, March 5, 2015 5:06PM - 5:18PM |
W25.00012: Sliding friction levels of water films on graphene measured by means of QCM Zijian Liu, Samuel Kenny, Zachary Fredricks, Jacqueline Krim Diffusion and sliding friction of water on graphene is a matter of great current interest [1]. To study the surface friction of water on graphene, we recorded water film adsorption on a graphene film coated quartz crystal microbalance (QCM). Graphene films were deposited on QCMs via evaporation in vacuum on nickel substrates. Measurements were performed with the QCM mounted in vacuum, and then water vapor was slowly introduced into the vacuum chamber until it reached saturation, while simultaneously monitoring the frequency and amplitude of the QCM. Negative shifts in frequency were observed, indicating that water vapor formed a film on the graphene film. The amplitude data was used to calculate the mechanical resistance and slip time for water molecules sliding on the graphene surface. The low slip time indicates a relatively low friction between a water film and graphene. Funding provided by NSF DMR. \\[4pt] [1] R. R. Nair et al. Science 335, 442 (2012) [Preview Abstract] |
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