Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session D33: Morphology Characterization: Frontier of Scattering and MicroscopyFocus
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Sponsoring Units: DPOLY Chair: Xiaodan Gu, Univ of Southern Mississippi Room: 505 |
Monday, March 2, 2020 2:30PM - 2:42PM |
D33.00001: Computational Reverse-Engineering Analysis for Scattering Experiments (CREASE) on Amphiphilic Block Polymer Solutions Arthi Jayaraman, Daniel J Beltran, Michiel Wessels In this talk we will present a new computational method titled ‘Computational Reverse-Engineering Analysis for Scattering Experiments’ or CREASE to interpret the intensity profiles obtained from small angle neutron scattering done on amphiphilic polymer solutions. For a given input comprised of scattering intensity profiles and information about the amphiphilic polymers in solution, CREASE uses a genetic algorithm that outputs the structure of the self-assembled micelles (e.g., core and corona diameters, aggregation number) and then through molecular reconstruction simulations describes the conformations of the amphiphilic polymer chains in the micelle (e.g., blocks’ radii of gyration, chain radii of gyration, monomer concentration profiles). The primary strengths of CREASE are its ability to analyze scattering profiles without an off-the-shelf scattering model and its ability to provide chain and monomer level structural information that is otherwise difficult to obtain from scattering and microscopy alone. |
Monday, March 2, 2020 2:42PM - 2:54PM |
D33.00002: Feature Engineering for Small-Angle Scattering Model Selection Yuke Wang, Tyler Martin While many soft-matter characterization techniques can be unambiguously interpreted to yield information about chemical and material structure, small-angle neutron and X-ray scattering (SANS and SAXS) data must be interpreted via a library of physical and phenomenological models. Complicating this task is the unavoidable phase problem, which causes scattering patterns to be non-unique and makes model selection a non-trivial task. Here we present our efforts in developing shallow- and deep-classifiers which, given a scattering dataset, suggest applicable models to the user. In particular, we will focus on our efforts in feature vector engineering i.e., the optimization of input parameters in order to maximize classification efficiency. We show that simple data transformations greatly increase our classification efficiency over a naïve model, allowing us to achieve greater than 99 % top-3 accuracy in the model-selection task. More broadly, these optimized feature vectors will enhance machine learning models for tasks other than model selection (e.g., error detection, automated experimentation, on-the-fly analysis). The ultimate goal of this project is to formalize feature vector design for small-angle scattering, thereby enabling the creation of bespoke machine-learning models. |
Monday, March 2, 2020 2:54PM - 3:06PM |
D33.00003: Identification of Frank-Kasper Phases in Conformationally Asymmetric Linear Block Copolymer Self-assembly Seungbae Jeon, Taesuk Jun, Seongjun Jo, Hyungju Ahn, Byeongdu Lee, Du Yeol Ryu The quasicrystalline phases which were originally observed in metal alloys have emerged with block copolymers (BCPs) self-assembly providing a new potential in soft materials. Theoretical and experimental studies have revealed that conformational asymmetry (ε) of the different blocks provides a key mechanism to stabilize the Frank-Kasper (FK) σ and A15 phases in BCPs self-assembly. In this work, polydimethylsiloxane-b-poly(2,2,2-triflouroethyl acrylate)s (PDMS-b-PTFEAs) were designed using flexible silicon-containing blocks and rigid fluorine-containing blocks to produce linear BCPs with a high conformational asymmetry. Evaluated value of ε was 2.20 which is higher than other BCPs reported in the literatures. A series of PDMS-b-PTFEAs were synthesized to produce compositionally asymmetric, PDMS-rich phases ranging from fPDMS = 0.746 to 0.869. Using small-angle X-ray scattering, the FK σ and C14 phases were observed at fPDMS = 0.80 and 0.85, respectively. Based on the fact that the stability of σ phase increases by the value of ε, we speculate that the stability level of the C14 phase as well as σ phase is due to the relatively high ε of PDMS-b-PTFEAs. |
Monday, March 2, 2020 3:06PM - 3:42PM |
D33.00004: Combining Advanced Experimental Methods to Characterization of Polymer Nanocomposites Invited Speaker: Karen Winey Each characterization method provides specific information about a polymer sample over a limited range of length and time scales. A comprehensive understanding of polymer morphology and dynamics is best developed by combining a set of characterization methods to capture a broader range of lengths and times. This talk will highlight examples from our studies of polymer nanocomposites that have combined methods to develop detailed and quantitative descriptions of these complex polymer systems. Specifically, the dynamics in polymer nanocomposites include segmental and chain-scale motion of the polymer, as well as diffusion of the nanoparticles. We apply ion beam methods (elastic recoil detection and Rutherford backscattering) and single particle tracking methods, as well as more accessible methods such as temperature-modulated DSC and broadband dielectric spectroscopy methods, to probe the molecular weight dependence of the polymer and nanoparticles are revealed for nanoparticles of various sizes and nanoparticle-polymer interactions. These vignettes will also serve to illustrate the capabilities of the individual methods and demonstrate the exceptional value of combining these advanced experimental methods. |
Monday, March 2, 2020 3:42PM - 3:54PM |
D33.00005: Deformation Mechanics during Drawing of Ultra-High Molecular Weight Polyethylene Fibers Christopher Henry, Giuseppe Palmese, Nicolas Alvarez There has been extensive study of Ultra-high molecular weight polyethylene (UHMWPE) fibers owing to their remarkable tensile modulus and strength. It is understood that these properties are generated during the post drawing process. Questions remain however, regarding how the morphology of the polymer develops during processing, and how this leads to the observed properties. Basic information regarding strain rate, stress at failure, and the role of processing parameters is missing due to the difficulty of measurement with industrial processes. This information is critical to understanding the polymer response during drawing. In this study we use a modified extensional rheometer (VADER 1000) to perform the drawing process on a series of UHMWPE fibers spun at Drexel. We have shown previously that ASF crystalline structure is not limited to the isotropic states typically seen in literature. With the VADER 100, and this broad range of starting materials we can monitor true stress and strain throughout the draw, and discover the mechanical properties prior to, and at, the failure point. Small and wide-angle x-ray scattering is used investigate the crystalline morphology. With this information a fundamental understanding of the post-drawing will be developed. |
Monday, March 2, 2020 3:54PM - 4:06PM |
D33.00006: 3D Structure of Grain Boundaries in Tubular Network Block Copolymers Xueyan Feng, Amanda Suarez, Derrick Ong, Kaiqi Yang, Hua Guo, Edwin Thomas Multi-continuous microphases (such as double gyroid) have network structures with 3D interconnected, self supporting domains. The properties of the component in each domain are strongly expressed due to the geometrical continuity in all three dimensions. However, the occurrence of grain boundaries (GB), which interrupt the topological and geometrical order of the continuous ordered networks, will significantly affect their performance. Here, we examine GBs in a polystyrene-b-polydimethylsiloxane double gyroid system using high fidelity 3D reconstructions made by Slice and View scanning electron microscopy (SVSEM). Since large amounts of GB can be reconstructed, we employ machine learning to extract the shape/distribution of the GB. Also, two types of GBs are identified and described (grain-grain tilt and order-disorder-order boundaries). Different types of irregular nodes/topological loops/network connections within the GB region are identified. The local topological parameters, as well as curvature of the intermaterial dividing surface, node functionality distribution, strut length/orientation distribution and surface to volume ratio in the GB are analyzed and compared with the same set of morphological descriptors measured in the adjacent, ordered double gyroid grains. |
Monday, March 2, 2020 4:06PM - 4:18PM |
D33.00007: Local density and free volume inhomogeneities govern transport properties in reverse osmosis membranes Michael Geitner, Tyler Culp, Jeffrey D. Wilbur, Steven Jons, Manish Kumar, Enrique D Gomez Developing a mechanistic description of how microstructure affects membrane properties could lead to the development of next-generation materials for desalination. Quantification of the internal microstructure of fully-aromatic polyamide thin-films, which serve as the active layer in state-of-the-art desalination membranes, is a crucial component to developing such descriptions. Here, we studied a series of reverse osmosis membranes showing systematic increases in water permeance over currently available membrane materials without sacrificing water-salt selectivity. We quantified the internal morphology of the polyamide active layers via scanning transmission electron tomography, where 3D reconstructions were obtained and parameters, such as void fraction and surface area, were measured. Tomogram intensity analysis revealed the nanometer-scale density and free volume distributions, used in conjunction with the 3D polyamide models to model water transport properties in such materials. The combination of density and free volume distributions determined from electron tomography with water transport modeling has provided a robust approach towards the development of structure-property relationships in reverse osmosis membranes. |
Monday, March 2, 2020 4:18PM - 4:30PM |
D33.00008: Three-Dimensional Imaging the Crystalline Structure of Polypeptoid Nanosheet with Atomic Resolution Xi Jiang, Sunting Xuan, Nan Li, David Prendergast, Ronald Zuckermann, Nitash Balsara Electron microscopy imaging of three-dimensional structures in soft materials with atomic resolution is challenging because soft materials are unstable under the electron beam, and techniques such as x-ray scattering or diffraction are not able to provide atomic resolution phase information in position space. The experiments were conducted on self-assembled crystalline polypeptoid nanosheets. Low-dose cryogenic electron microscopy micrographs were obtained from frozen hydrated crystalline nanosheets on the novel ultra-flat supporting grid at different tilting angles. A hybrid processing of crystallographic, tomography and single particle methods, developed for cryo-electron microscopy of biological macromolecules, was used to resolve the structure of crystals with atomic resolution in three dimensions. Our approach is robust and enable direct visualization of the arrangement of polypeptoid backbones and side chains in crystalline nanosheets. It also revealed the effect of side chain chemistry on the crystalline structure of polypeptoid nanosheets. |
Monday, March 2, 2020 4:30PM - 4:42PM |
D33.00009: Pushing the resolution limits for imaging conjugated polymers in the transmission electron microscope Brooke Kuei, Enrique D Gomez Transmission electron microscopy (TEM) of conjugated polymers has remained a challenge because resolution is limited by the electron dose the sample can handle. We have characterized beam damage in poly(3-hexylthiophene) (P3HT), poly(3-dodecylthiophene-2,5-diyl) (P3DDT), and poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3’’’-di(2-octyldodecyl)-2,2’;5’,2’’;5’’,2’’’-quaterthiophene-5,5’’’-diyl)] (PffBT4T-2OD) via electron diffraction and electron energy-loss spectroscopy (EELS). Critical dose DC values were calculated from the decay of diffraction and low-loss EELS peaks as functions of dose rate, temperature, and beam size. At room temperature, DC first increases then decreases with increasing dose rate, whereas at cryogenic conditions this dose rate dependence is less pronounced and the overall DC increases; these results suggest that a significant mechanism for beam damage in conjugated polymers is diffusion of secondary free radicals. DC also increases with decreasing beam size. These new concepts in beam damage revealed strategies to push the resolution in the TEM, allowing us to image 3.6 Å π-π stacking in PffBT4T-2OD with 4D STEM, high-resolution TEM (HRTEM) at cryogenic conditions, and HRTEM at room temperature with antioxidants. |
Monday, March 2, 2020 4:42PM - 4:54PM |
D33.00010: Observation of Elongated Nano Domains in Organic Photovoltaic Active Layers with Electric Field Treatment using Cross-Sectional Scanning Tunneling Microscopy and Spectroscopy. Rabindra Dulal, Akshay Iyer, Umar Ghumman, Joydeep Munshi, Aaron Wang, Ganesh Balasubramanian, Wei Chen, Te-Yu Chien The effects of the electric-field-assisted annealing on the bulk heterojunction nano-morphology in the P3HT/PCBM active layer of the organic photovoltaic cells (OPVCs) are presented here. It was widely accepted that the electric field will facilitate the P3HT, the polar polymer, to be better crystallized hence enhance the charge mobility and improve the OPVC performance. However, the effects on the nano-morphology in the active layer treated with the electric field are not well understood. Here, by utilizing the cross-sectional scanning tunneling microscopy and spectroscopy (XSTM/S), it is revealed that the electric-field-assisted annealing will facilitate the P3HT-rich domains formed elongated shape with the orientation close to the direction of the external electric field which is beneficial to the OPVC charge collection. On the other hand, it was also observed that the electric-field-assisted annealed samples showed smaller energy gaps and smaller energy off-set between the molecular domains which might negatively impact the charge separation efficiency. The XRD and SAXS results indicate that the smaller energy gaps might be caused by the molecular intermixing. These results point out competing factors affecting the OPVC performance. |
Monday, March 2, 2020 4:54PM - 5:06PM |
D33.00011: Directly Visualizing Conformations of Bottlebrush Polymers in Bulk Films using Super-Resolution Optical Microscopy Jonathan Chan, Avram Kordon, Zhe Qiang, Muzhou Wang Bottlebrush polymers have advantageous photonic and mechanical properties that are well suited for applications such as coatings, pigments, and super-soft materials. This architecture consists of a polymer backbone densely grafted by side chains, whose steric repulsions result in rigid, elongated conformations. While the single-chain conformations of these polymers have been studied experimentally for isolated chains on surfaces and within dilute solutions, few studies have probed their conformations in bulk environments. In this work, we directly visualize individual bottlebrush polymers in a bulk environment populated by other bottlebrushes, by mixing dilute quantities of fluorescently-labeled chains with unlabeled polymers and imaging through super-resolution optical microscopy (SROM). Using SROM, we resolved individual chains within thin films of bulk polymers and found the tangent correlation functions (TCFs) of the backbone. These TCFs were fit to a worm-like chain model, and values for the persistence length were extracted to quantify rigidity. Changes to these conformations were observed with variations to architectural parameters such as side chain length and grafting density. |
Monday, March 2, 2020 5:06PM - 5:18PM |
D33.00012: Kinetically Controlled Morphology in Copolymer-based Hydrogels Crosslinked by Crystalline Nanodomains Determines Efficacy of Ice Inhibition Pablo Sepulveda-Medina, Chao Wang, Bryan Vogt Confinement of water within physically crosslinked hydrogels can alter the physics associated with the water within the hydrogel. When water is confined between hydrophobic nanodomains that act as physical crosslinks, crystallization of water can be dramatically inhibited. In prior work, the inter-nanodomain spacing was controlled by changing the fraction of hydrophobic segments in the polymer, which leads to an inverse correlation between water content and confinement extent. However, water content and confinement effect have not been decoupled. Here, we decouple confinement and water content through kinetically controlled nanostructure in a hydrogel crosslinked by crystalline nanodomains based on 2-hydroxyethyl acrylate (HEA) and n-octadecyl acrylate (ODA). Zone annealing of the dry copolymer alters the structure of the crystalline ODA domains that effectively crosslink the hydrogel. Despite these changes in the ODA structure, the average hydrogel water content was not significantly altered. However, the unfrozen water inside the hydrogel varies from 60 to 99 wt%, determined from DSC and in-situ WAXS. The antifreeze efficacy is found to correlate directly with the structure where smaller spacing leads to higher unfrozen water fraction. |
Monday, March 2, 2020 5:18PM - 5:30PM |
D33.00013: Morphological Investigations of Anion-Conducting Polymer-Catalyst Interface Nora Buggy, Yifeng Du, Mei-Chen Kuo, Bryan Coughlin, Andrew Herring The heterogeneous microstructure of the electrode in polymer electrolyte-based electrochemical devices is not well understood. This is due in part to complex interactions between the ion-conducting polymer (ionomer), catalyst particles, and carbon. It is known that interactions at the polymer-catalyst interface induce restructuring that propagates through the bulk morphology of the material [1]. This is potentially to the detriment of species transport in the electrode, ultimately affecting device performance. |
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