Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session W34: Polymers Under Extreme Environmental ConditionsFocus
|
Hide Abstracts |
Sponsoring Units: DPOLY GSCCM DCP Chair: Nir Goldman, Lawrence Livermore Natl Lab Room: 506 |
Friday, March 6, 2020 8:00AM - 8:12AM |
W34.00001: Anisotropic hydrolysis susceptibility in deformed polydimethylsiloxanes Matthew Kroonblawd, Nir Goldman, James Lewicki Environmental factors such as humidity have potential to drive chemical degradation of polymer networks in ways that compound with mechanical stressors. Using two levels of quantum chemical theory, we identify a possible electronic driver for strain-induced chemical susceptibility in deformed polydimethylsiloxane (PDMS) chains. High throughput sampling with a validated semiempirical density functional tight binding (DFTB) model is used to explore the complicated interplay between hydrolytic chain scissioning reactions, mechanical deformations of the backbone, water attack vector, and chain mobility. We show that sustaining tension through concerted strains of the backbone over at least a few monomer units is necessary to significantly increase hydrolysis susceptibility. A reactive order parameter is developed that describes chain scission probabilities as a complicated function of the backbone degrees of freedom. The trends identified suggest simple physical descriptions for the synergistic coupling of local mechanical deformation and chemistry in silicones. |
Friday, March 6, 2020 8:12AM - 8:24AM |
W34.00002: Relating Electrical Properties of Highly Disordered Insulating Materials via the Dispersion Parameter Zachary Gibson, John R Dennison Relations between electrical properties, critical transitions (CT), and the dispersion parameter α for highly disordered insulating materials (HDIM) are presented. The dispersion parameter is often defined as the thermal energy (low field regime) or field energy (high field regime) scaled by a material-dependent characteristic energy (energetic width of DOS within mobility gap). For dispersive transport, 0<α<1; α=1 defines a CT in both temperature (T) and electric field. A kink is observed in double logarithmic current-time plots measured at constant voltage, similar to Scher-Montroll curves for pulsed photoconductivity. Dark conductivity measurements transition from T-1 to T-1/4 dependence on a double logarithmic current-T plot at the temperature CT, indicative of a transition from multiple trapping to variable range hopping dominated transport. A field CT is apparent in pulsed electroacoustic measurements of charge distributions where normal transport is observed at high fields, corresponding to the onset of normal transport and electrostatic breakdown. As an example of a prototypical HDIM, various measurements are presented for low-density polyethylene. |
Friday, March 6, 2020 8:24AM - 8:36AM |
W34.00003: Atomistic analysis of PBO carbonization process with ReaxFF Reactive Force Field Malgorzata Kowalik, Chowdhury M. Ashraf, Siavash Rajabpour, Behzad Damirchi, Dooman Akbarian, Qian Mao, Adri C.T. van Duin There is a constant need for an alternative precursor polymer for the carbon fibers (CFs) production with lowering the costs without compromising CFs mechanical properties. We report an atomistic simulation of a direct carbonization of poly(p-phenylene-2,6-benzobisoxazole) (PBO) that can be transform into high strength carbon fiber. The possibility of using various heating rates is considered and observed gaseous molecules as well as 6-membered all-carbon ring production analyzed. Based on our ReaxFF atomistic-scale reactive molecular dynamics simulations of the direct carbonization of the PBO we proposed a mechanism that might be responsible for an improvement of the mechanical characteristics of the PBO-based CFs with ultrafast heating rate treatment observed in experiment. |
Friday, March 6, 2020 8:36AM - 8:48AM |
W34.00004: Characterization of the shock response of heterogenous polymer foams using multi-point PDV measurements John Lang, Rachel Huber, Katie Maerzke, Dana Dattelbaum SX358 is a cross-linked polydimethylsiloxane (PDMS) that can be synthesized in a range of densities (0-65% porous). When porous, it is a stochastic, open cell heterogenous foam with varying pore sizes (10-1000s µm). To model SX358, experimental data is needed to inform equation of state (EOS) models over the range of initial densities. Gas gun planar impact was used to measure high pressure, high temperature material response and shock compression with traditional configurations and diagnostics. The results vary widely, which we attribute to the heterogenous structure of the foam. The diagnostics may interrogate areas where the local density is less than (e.g., a large pore) or greater than the average density. To explore pore variability, we interrogated a large sample area with many velocimetry probes, and then combined the data to obtain an ‘average’ material response. As with past experiments the individual probes showed a varied response. When the data are combined, the ‘average’ response provides a better measure of the continuum response of the stochastic foam with a reduced uncertainty. Phase contrast imaging of the propagating shock front and velocimetry diagnostics with interrogation areas larger than the pore sizes are under investigation to better constrain the EOS. |
Friday, March 6, 2020 8:48AM - 9:00AM |
W34.00005: Investigating the Shock Properties of Polycarbonate James Hawreliak Polycarbonate is an impact resistant optically transparent thermal plastic used in many engineering applications. The optical transparency and low-Z composition of the polymer chains which make up polycarbonate have made it a candidate window material for dynamic compression experiments. Specifically, experiments which uses x-rays to probe the lattice structure. The low-Z allows for high x-ray transmission and low x-ray scattering for performing x-ray diffraction experiments to measure the atomistic properties, and the optical transparency is suited for using optical probes to measure the bulk material response. We present measurements of the optical properties of polycarboante at 1550nm and 532nm, the two waves lengths used for velocity interferometery in shock wave experiments. |
Friday, March 6, 2020 9:00AM - 9:12AM |
W34.00006: Polyimide Two-Wave Structure Produced by Shock Compression Rachel Huber, Brian Bartram, Dana Dattelbaum, Lloyd L GIbson, John Lang Polymeric materials undergo densification when dynamically compressed, transitioning the polymer from reactants to products. During gas gun-driven planar impact, we can observe this decomposition with velocimetry probes capturing the particle velocity (movement of the material) history that results from the impinging shock wave. This transition produces a shock wave for both the reactants and the products. If the volume change is large enough, the reactants wave will separate from products wave, generating a two-wave structure in the velocimetry profiles. If the polymer is shocked above or below this transition region, a single wave will be observed. Polyimide (PI) is composed of imide monomer units (-OC2-NC-C2O-); it is used as a thermoplastic for high pressure, high temperature applications. Understanding how this polymer reacts within its transition region (17.8-30 GPa) provides vital information for equation of state (EOS) modeling. PI has a large volume change, 20.3%, when shocked into its transition region. Through gas gun-driven planar impact we have observed a two-wave structure in PI with velocimetry probes. The two-wave structure measurement provides kinetic parameters for the reactants-to-products transition that informs the kinetics for EOS models. |
Friday, March 6, 2020 9:12AM - 9:48AM |
W34.00007: 3D-printed polymeric foam under constant compressive strain: constitutive and multiscale models of long-term property changes Invited Speaker: Amitesh Maiti Cellular solids or foams constitute an important class of materials with diverse applications. Traditional processes to create such materials lead to significant dispersion in pore size, shape, thickness, and topology. However, recent LLNL advances in 3D printing of polymeric foams by direct-ink-write has enabled the creation of cellular materials of programmable microstructure, customizable shapes, and tunable mechanical response. Success of these 3D printed parts as viable replacement for traditional stochastic foams depends critically on their performance and stability under long-term mechanical strain. To study such effects, we carried out accelerated aging experiments on foams, both stochastic and 3D printed, under a state of constant compression. We monitored the time-evolution of permanent structural change (compression set), altered load-bearing capacity, and changed modulus. This talk will highlight several recent results based on the above measurements, including: (1) the prediction of long-term property changes through time-temperature superposition, with uncertainty margins created using statistical bootstrap; (2) the development of an “age aware” constitutive materials model using the Ogden hyperfoam formalism in a Tobolsky two-network scheme; and (3) finite-element stress analysis within X-ray-CT-imaged foam microstructures that illustrates the superior stability of certain 3D printed close-packed frameworks. The basic steps to a reptation-tube-encompassing coarse-grained strategy to model macroscale aging effects in rubber will also be discussed. |
Friday, March 6, 2020 9:48AM - 10:00AM |
W34.00008: Features of shock Hugoniot measurements of underdense materials Dana Dattelbaum, Joshua Coe, Brittany Branch An important challenge pertaining to equation of state model improvements for underdense materials is the quality of experimental measurements. A recent analysis of errors associated with historical explosively-driven experiments yielded large values (>10%) – due, in part, to the near-equivalencies of the shock and mass velocities, which give rise to large errors in density, and spatiotemporal limitations on diagnostics. Other challenges include material heterogeneity and high shock temperatures, both of which contribute to difficulties in experimental measurements. Shock heating, for exmaple, can dominate the compressive response resulting in “anomalous compression.” In the anomalous regime, the Hugoniot curves often bend back, with increases in shock pressure resulting in no volume change, even at modest porosities. We present a summary of features of shock Hugoniots of porous polymers over a range of initial densities, and show the interplays between initial density, shock stress, and normal vs. anomalous regimes. We also describe how penetrating x-ray-based imaging can be used to drive down errors. Recommendations will be made for future improvements and their impacts on theoretical model development. |
Friday, March 6, 2020 10:00AM - 10:12AM |
W34.00009: Efficient Shockwave Energy Dissipation in Dynamic PDMS Networks Christopher Evans, Nancy Sottos, Jaejun Lee, Laura Porath, Brian Jing Polymer networks containing dynamic bonds have received increasing attention over the past decade. Depending on the specific bond, a certain amount of energy is required for the bonds to undergo an exchange process. We hypothesize and demonstrate that dynamic bonds in polydimethylsiloxane (PDMS) networks can be used as an effective mechanism for dissipating energy, in particular from a shockwave. The density of dynamic bonds can be controlled which controls the modulus while the network Tg is unchanged. Using a classical laser induced shockwave technique, superior energy dissipation is observed in a PDMS dynamic rubber compared to the benchmark polyurea. The dynamic PDMS also outperforms covalently crosslinked PDMS and shows a monotonic improvement in dissipation performance with increasing density of dynamic boronic ester bonds. In all cases, the Tg is invariant in the different networks (-125 °C) implying a minimal role of segmental dynamics on dissipation in these specific networks. The dynamic networks can be shocked multiple times with invariant performance suggesting the mechanism is non-destructive and related to bond exchange rather than breakage. |
Friday, March 6, 2020 10:12AM - 10:48AM |
W34.00010: Synthesis and Self-Assembly of Multi-Patch Functional Colloids Invited Speaker: Alexander Böker This talk will discuss the creation of artificial materials systems which can be programmed to self-assemble and may even allow self-replication of structures. To achieve this, an indispensable prerequisite is the multi-directional control of interactions between the building blocks of materials. Thus, we describe a new class of multi-patch colloidal particles via an advanced micro-contact printing technique yielding patches of different chemical or physical functionalities. The new production process allows precise control over the patch location and chemistry even with low molecular weight inks and thus also yields particles that go well beyond known ABA- or ABC-type Janus particles. In addition chemical approaches for selective interaction and their influence on the self-assembly behavior will be discussed[1-5]. |
|
W34.00011: Surface hardness enhancement of ion bombarded polycarbonate Sunmog Yeo, Chang Young Lee, Won-Je Cho, Yong-Seok Hwang, Chorong Kim, Dong-Seok Kim The surface hardness of polycarbonate (PC) can be enhanced by ion bombardment with energy of a few hundred KeV. Nano indentation measurement on ion bombardment PC shows that the hardness of PC increases with increasing the ion dose. In addition, the surface properties examined by FT-IR show that the lighter ion mass causes the increase of C=O (1680-1750 cm-1) and C=C (1500-1700 cm-1) stretching vibration and the relative ratio of C-O-C peak near the wave number of 1200 cm-1 decreases with increasing dose and energy of H+ ion. We discuss the surface hardness enhancement of PC based on these results. |
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