Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session H43: Advancing Polymer Physics by Integrating Simulation and Theory II |
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Sponsoring Units: DPOLY DCOMP Chair: Jonathan Whitmer, Univ of Notre Dame Room: LACC 503 |
Tuesday, March 6, 2018 2:30PM - 3:06PM |
H43.00001: Break - Dillon Medal Talk
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Tuesday, March 6, 2018 3:06PM - 3:18PM |
H43.00002: “On the fly” QM/MM hybrid simulations of critical failure at the interface in CNT/polymer nanocomposites Jacek Golebiowski, Peter Haynes, Arash Mostofi Functionalised CNT/polymer composites are a class of strong, lightweight materials with application in many areas of technology, including aerospace. Developing a fundamental understanding of failure mechanisms at the CNT/polymer (CNP) interface can lead to making better materials suited to a broader range of applications. |
Tuesday, March 6, 2018 3:18PM - 3:30PM |
H43.00003: Prediction of ionic conductivity and transport mechanism in polymer electrolytes using molecular dynamics jonathan mailoa, Nicola Molinari, Georgy Samsonidze, Boris Kozinsky Polymer solid electrolytes are promising for Li-metal batteries because of easy processing, and better safety than liquid electrolytes. However, Li-ion diffusivity in the most widely used polymer (polyethylene oxide, or PEO) is relatively low. Considering the vast landscape of polymer compounds, there is a need to narrow down and identify new promising polymers with better Lithium ion transport through atomistic simulation methods. In this work, we develop a molecular dynamic simulation (MD) model which enables prediction of Li ion conductivity in various polymer systems at high Li-salt concentration. The model methodology and ionic conductivity experimental validation will be presented for polymers with various high Li-salt concentrations typical in real Li-polymer batteries. We highlight the importance of atom partial charge determination using quantum chemistry in order to ensure accuracy of the model. We also analyze the transport mechanism in the PEO, and explain how modifying polymer geometry & chemistry can activate a different transport mechanism which may enable better Li-ion transport in novel polymer systems. |
Tuesday, March 6, 2018 3:30PM - 3:42PM |
H43.00004: Computational study of mechanical properties of poly-phenylene terephthalamide Jie Yu, Giacomo Fiorin, Haowei Peng, Michael Klein, John Perdew We explore the mechanical properties of poly-phenylene terephthalamide (PPTA) by density functional theory calculations. We compare the results from LDA, PBE, PBE+rVV10, SCAN, and SCAN+rVV10, with the experiment. Among them SCAN shows the best performance in predicting the lattice constants of PPTA along the two crystal directions involving van der Waals (vdW) interaction and hydrogen-bond interaction. We study the mechanical response of PPTA as well by applying strain along three lattice directions. A clear observation is that the PBE functional does not capture any vdW interaction and exhibits a non-bonding energy curve. Due to the inclusion of vdW interaction, SCAN, PBE+rVV10, and SCAN+rVV10 all exhibit bonding energy curves. The equilibrium lattice constants obtained by SCAN and PBE+rVV10 are close to experimental data while SCAN+rVV10 slightly over-binds the system. We compute the Young’s modulus and yield strength of PPTA, and find that the experimental data are much smaller than computationally predicted values, partly due to the fact that these samples consisting of fibers are mechanically weaker than perfect molecular crystals. |
Tuesday, March 6, 2018 3:42PM - 3:54PM |
H43.00005: Electronically excited states in π/π stacking compounds Azusa Muraoka, Nao Fukabori, Tomomi Yasoshima In particular, π/π stacking compounds have become of interest in new materials for photocatalysis, solar energy and phosphorescent organic light-emitting diodes. We investigate theoretically the photo-induced charge transfer in supramolecular chemistry such as a bowl-shaped polycyclic hydrocarbon and helical ortho-position linked phenylenes (OPs). The electronically excited states and absorption spectra of these materials were first studied by using TD- DFT calculations with various functionals. The functional that best reproduced the experimental results was found to be wB97XD, and the assignment of the experimentally observed UV-Vis absorption spectrum was successfully performed in comparison with the theoretically obtained one. We especially performed spectral assignment of the carbazole (Cz) -modified OP complexes. The results showed that the absorption spectrum of the complexes consisted of (i) an n–π* charge-transfer type transition from Cz to OPs units of longer wavelength at around 290 nm and the π–π* transition of a shorter wavelength at around 230 nm, and (ii) the components of three isomers which coexist with three kinds of substitution of Cz to OPs, such as ortho, meta and para linkage of Cz, to interconnect the aromatic units of the Ops. |
Tuesday, March 6, 2018 3:54PM - 4:06PM |
H43.00006: Coarse-grained potentials to perform large scale molecular dynamics simulations of graphene sheets self-assembling at the water-oil interface Vikram Reddy Ardham, Frédéric Leroy Water-oil interfaces provide excellent templates to synthesize networks of graphene flakes, only up to a few layers thick. To simulate and study such systems using particle based simulations, we derive force-fields for particle-liquid interactions relying on the wetting coefficient (ω) as the parameter to provide the criterion. Using molecular dynamics, we simulate a composite system containing water-n-hexane interface and a graphene sheet at various values of ω to evaluate the boundaries for which the particle adsorbs at the interface. At the two resolutions studied (atomistic and coarse-grained) we observe that the boundaries for values of ω that allow monolayer graphene to adsorb at the interface are very consistent with the predictions made for thick macroscopic particles. We confirm our results by evaluating potentials of mean force of the system as a function of the particle’s separation from the interface. Further, we illustrate the applicability of method by simulating a relatively large water-oil interface with many graphene particles adsorbing at the interface using the derived coarse-grained model. The method might find applications in multi-scale modeling of polymer nanocomposites where a great deal of solid-liquid interface is to be modelled accurately. |
Tuesday, March 6, 2018 4:06PM - 4:18PM |
H43.00007: Hierarchical excluded volume screening in solutions of bottlebrush polymers Jaroslaw Paturej, Torsten Kreer Polymer bottlebrushes provide intriguing features being relevant both in nature and in synthetic systems. While their presence in the articular cartilage optimizes synovial joint lubrication, bottlebrushes offer pathways for fascinating applications, such as within super-soft elastomers or for drug delivery. However, the current theoretical understanding lacks completeness, primarily due to the complicated interplay of many length scales. During the talk analytical model will be presented which demonstrates how structural properties of bottlebrushes depend on the concentration, ranging from dilute solutions to highly concentrated melts. The validity of our model is supported by data from extensive molecular dynamics simulations. We demonstrate that the hierarchical structure of bottlebrushes dictates a sequence of conformational changes as the solution concentration increases. The effect is mediated by screening of excluded volume interactions at subsequent structural parts of the bottlebrushes. Our findings provide important insights that should enable improved customization of novel materials based on the architectural design of polymer bottlebrushes. |
Tuesday, March 6, 2018 4:18PM - 4:30PM |
H43.00008: Routine million-particle simulations of epoxy curing with dissipative particle dynamics Stephen Thomas, Eric Jankowski Mesoscale simulation techniques have helped to bridge the length and time scales needed to predict the microstructures of cured epoxies, but the prohibitive computational cost of simulating experimentally relevant system sizes has limited their impact. In this work we develop an open-source plugin for the molecular dynamics code HOOMD-Blue that permits epoxy crosslinking simulations of millions of particles to be routinely performed on a single modern graphics card. Using these capabilities, we are able to use ensembles of epoxy processing pathways to obtain realistic bond kinetics and relaxation times that sensitively depend on stochastic bonding rates and a diffusive drag parameter. This work also demonstrates the first implementation of fully customizable temperature-time curing profiles with dissipative particle dynamics. Finally, we evaluate the ability of this model to predict the mechanical properties that result from a variety of curing profiles and chemistries for a classic epoxy/hardener/toughener system and quantify the relationship between the temperature-time curing profile and resultant molecular microstructure. |
Tuesday, March 6, 2018 4:30PM - 4:42PM |
H43.00009: Structure and Mechanics of Semi-Crystalline Polymers: Coarse-Grained Simulation and Theory Tyler Martin, Ronald Jones, Chad Snyder Semi-crystalline polymers are a class of polymers which have interconnected crystalline and non-crystalline (amorphous) regions in their microstructure and are used in applications ranging from piping to photovoltaics to food packaging due to their favorable mechanical, wear, electronic, and barrier properties. Despite their near-ubiquitous use, our understanding of semi-crystalline polymer microstructure (morphology/topology) and its connection to macroscopic mechanical properties is far from complete. Many past theoretical studies have attempted to explain semi-crystalline morphology with varying degrees of success, but recent experimental studies are challenging some of these theoretical explanations. In this talk, we will highlight our attempts to use modern molecular simulation and theory techniques to better understand the morphology-mechanics connection in semi-crystalline polymeric materials. This study expands our understanding of a large-class of polymeric materials and will improve material scientists’ and synthetic chemists’ ability to create semi-crystalline polymeric materials with optimal and targeted properties. |
Tuesday, March 6, 2018 4:42PM - 4:54PM |
H43.00010: Comparing Dynamics via Atomistic Simulations with Mechanics via Experiment: Utility of the Time-Temperature Superposition Principle Ketan Khare, Frederick Phelan Jr. Large system size and computationally inaccessible timescales makes quantitative comparison of atomistic simulations and experiment non-trivial for polymer networks. Recently, we studied the temperature trend of the specific volume for an epoxy system using multiple cooling rates in conjunction with the time-temperature superposition principle (TTSP) and showed that this permits a direct quantitative comparison of simulation and experiment, bridging a ten order of magnitude mismatch in the respective rates. Here, we show that the time and temperature trend of the mean squared displacement can be used to create a master curve that incorporates the temporal effects at a convenient reference temperature. The features of this master curve relevant to the glass transition show quantitative agreement with published experimental data for creep compliance. Similar to our previous study, the use of the TTSP allows us to use simulations at elevated temperatures to bridge an eight order of magnitude mismatch in computational and experimental timescales. The integration of molecular resolution atomistic simulations with established experimental methods for the study of the thermo-mechanical properties of polymer networks holds tremendous promise for progress in materials research. |
Tuesday, March 6, 2018 4:54PM - 5:06PM |
H43.00011: Shock-induced Para-crystallinity in PPTA Subodh Tiwari, Sungwook Hong, Paulo Branicio, Rajiv Kalia, Aiichiro Nakano, Priya Vashishta The outstanding strength-to-weight ratio of para-aramid fibers, such as Kevlar and Twaron, can be largely attributed to their high content of p-phenylene terephthalamides (PPTA) crystals. Here, we perform non-adiabatic shock loading on large PPTA crystal models along different low-index crystallographic directions using reactive molecular-dynamics simulations. Results reveal an anisotropic shock response displaying elastic, plastic, and phase transformation from crystalline to para-crystalline configuration. The simulation results provide an atomistic view on the effects of shock in para-aramid synthetic fibers. |
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