Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session B9: Multimodal Characterization of Soft Materials in Complex Environments IFocus
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Sponsoring Units: DPOLY Chair: Cheng Wang, LBNL Room: 268 |
Monday, March 13, 2017 11:15AM - 11:51AM |
B9.00001: Recent instrumentation advances offer new opportunities in electron microscopy of polymers Invited Speaker: Enrique Gomez Imaging of polymers by transmission electron microscopy (TEM) or scanning transmission electron microscopy (STEM) remains a challenge due to the low contrast between domains and sensitivity to the electron beam. Recent advances in instrumentation for electron microscopy have aimed to push the resolution limit, leading to remarkable instruments capable of imaging at 0.5 {\AA}. But, when imaging soft materials, the resolution is often limited by the amount of dose the material can handle rather than the instrumental resolution. Despite the strong constraints placed by radiation sensitivity, recent developments in electron microscopes have the potential to advance polymer electron microscopy. For example, monochromatated sources enable spectroscopy and imaging based on the valence electronic structure, aberration correctors enable imaging of thick films, direct electron detectors minimize the required dose for imaging, and differential phase contrast imaging can map heterogeneities in electric fields within films. Altogether, the field of polymer electron microscopy is poised to make significant advances in the near future. [Preview Abstract] |
Monday, March 13, 2017 11:51AM - 12:03PM |
B9.00002: Organic semiconductor material structure measurement by Polarized Resonant Soft X-ray Scattering Dean DeLongchamp, Brian Collins, Eliot Gann, Daniel Fischer The quest for structure-property relationships in organic semiconductors has driven significant advances in soft matter characterization techniques over the past decade. Despite this progress, surprisingly little consensus has been reached on what aspects of organic semiconductor film structure affect electronic properties. Although order and orientation must matter, at what length scales are they relevant? A molecular-scale picture -- the most difficult to obtain, particular in soft materials - may ultimately be required. I will describe our approach to resonant soft X-ray scattering, which combines principles of spectroscopy, small-angle scattering, real-space imaging, and molecular simulation to produce a molecular scale structure measurement for soft materials and complex fluids. [Preview Abstract] |
Monday, March 13, 2017 12:03PM - 12:15PM |
B9.00003: A Close Look at the Structure of Polymers with Soft X-rays: Insights from Theory and Experiment Gregory Su, Shrayesh Patel, Isvar Cordova, Michael Brady, David Prendergast, Michael Chabinyc, Cheng Wang Continued advances in the performance of polymer-based applications depends on an understanding of the connections among chemistry, structure, and dynamics in polymeric materials. These relationships are difficult to probe, especially under \textit{in situ} or \textit{operando} environments, and simulations are needed to unravel experimental results. We show how first-principles calculations of soft X-ray absorption spectroscopy can help understand the fundamentals of electronic structure in conjugated polymers, and elucidate structural parameters such as backbone tilt or polymer chain axis orientation. The important effects of various molecular parameters such as polymer chain length, side chain atoms, and backbone orientation on simulated spectra is demonstrated for model conjugated polymer systems. Core-level spectroscopy, which is sensitive to chemical moieties and electronic structure, is closely linked to resonant scattering that can additionally reveal spatial information. Progress in theory is also needed to connect spectroscopic and scattering techniques. The combination of these methods is evolving to probe chemistry and morphology of soft matter in a time-resolved manner. [Preview Abstract] |
Monday, March 13, 2017 12:15PM - 12:27PM |
B9.00004: Using resonant x-ray scattering to determine how structure controls the charge generation process in PCPDTBT:PC$_{\mathrm{70}}$BM solar cells Michael Pope, Matthew Waldrip, Thomas Ferron, Brian Collins Increased solar power conversion efficiencies to 12{\%} in bulk heterojunction organic photovoltaics (OPVs) continue to brighten their prospects as an economically viable source of solar energy. It is known that OPV performance can be enhanced through processing additives that change the nanostructure. We track these critical structure-property relationships in the OPV system PCPDTBT:PC$_{\mathrm{70}}$BM while varying the amount of DIO additive. Resonant Soft X-ray Scattering reveals domain purity, domain size, and molecular orientation to highlight the system's complex dependence on DIO concentration. We will show the effect the resulting structure has on charge generation and recombination via in-situ transient and steady state optoelectronic measurements. By measuring structure, excited state dynamics and device performance all on the same sample enables direct relationships to be measured. We show that the appropriate balance of crystallinity, domain size and domain purity are important for optimized excited state dynamics and device performance. [Preview Abstract] |
Monday, March 13, 2017 12:27PM - 12:39PM |
B9.00005: Illumination Alters the Conformation, Assembly and Thermodynamics of Conjugated Polymers Mark Dadmun, Brian Morgan Our group has recently completed a series of experiments that document the impact of illumination on the conformation, assembly, and thermodynamics of conjugated polymers. We have used small angle neutron scattering and reflectivity to monitor the impact of the presence of light on the changes of conjugated polymers in dilute and gel-forming solutions, as well as the self-assembly of conjugated polymer composite thin films. Ultimately, these works cumulatively provide strong evidence that light exposure dramatically alters the conformation and assembly of conjugated polymers in solutions and the melt. This can have far-reaching implications on the processing of organic electronic materials. Overlooking illumination conditions and failing to provide a consistent ambient light environment throughout device fabrication will result in non-uniform chain conformations and layering architectures, inevitably impacting device performance. However if properly understood and harnessed, these light-induced effects could make possible an entirely novel methodology for in-situ tuning of organic electronic device physical parameters. [Preview Abstract] |
Monday, March 13, 2017 12:39PM - 12:51PM |
B9.00006: Deuteration and neutron scattering: a powerful pair in polymer characterizations Kunlun Hong The complete characterization of a polymeric material in solution, as well as in bulk or thin films, requires an array of analytical techniques. Scattering techniques, including light, neutrons, and X-Rays, have proven to be essential analytical tools in characterizing polymers because they provide a non-invasive probe of structure, interactions, and dynamics of polymers over a wide range of length and timescales. The basic scattering techniques are well-established, and there are numerous reports about scattering in polymers. Here we show the use of neutron scattering techniques coupled with precise synthesis, especially with selective deuteration, to understand the structures of poly(3-alkylthiophene) derivatives. [Preview Abstract] |
Monday, March 13, 2017 12:51PM - 1:03PM |
B9.00007: Deuteration effect in RSOXS by using polystyrene side-chains Xiaodan Gu, Tadanori Kurosawa, Hongping Yan, Cheng Wang, Michael Toney, Zhenan Bao Deuteration of hydrogen atoms for polymer has been widely used in neutron scattering community to tune the contrast (a.k.a neutron scattering length) of a given material. Different polymers were synthesized with targeted contrast to cater different morphology characterization requirements. Here we present a similar "deuteration effect" for conjugated polymers using a PS side-chain for resonant soft X-ray scattering (RSOXS). By incorporating different amount of polystyrene side-chains to conjugated polymer, the scattering contrast between two-conjugated polymers could be easily enhanced or reduced, in a similar way that deuteration effect in neutron scattering. With only 10{\%} of polystyrene side-chain attached to a polymer backbone, the scattering contrast between conjugated polymer blends is improved by 170 times. This methodology could provide new way to consider when characterizing inherent low contrast between conjugated polymers blends. [Preview Abstract] |
Monday, March 13, 2017 1:03PM - 1:15PM |
B9.00008: Direct imaging of nanobubble Ostwald ripening using graphene liquid cell TEM Cong Xu, Qian Chen, Steve Granick We directly image the growth, morphology evolution and interaction dynamics of gas nanobubbles in a thin liquid, which are relevant to many materials and electrochemical processes. Using the recently emergent liquid phase transmission electron microscopy (TEM), we resolve the dynamics of nanobubbles \textit{in situ} at nm resolution in real time. We find that nanobubbles grow through an Ostwald ripening-like process, where adjacent bubbles stochastically fluctuate to disappear or enlarge. Capability of feature tracking enables us to characterize the motions and shape fluctuations of nanobubbles, providing insights into the gas-liquid interfacial fluctuations explored at the nanoscale. [Preview Abstract] |
Monday, March 13, 2017 1:15PM - 1:27PM |
B9.00009: Minimizing beam damage in the electron microscope to enable new imaging approaches for conjugated polymers 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 the effects of beam damage on poly(3-hexylthiophene) (P3HT) 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 scanning TEM electron energy-loss spectroscopy (STEM-EELS). Critical dose D$_{\mathrm{C}}$ values were calculated from the decay of diffraction and low-loss EELS peaks as a function of dose rate, accelerating voltage, and temperature. Importantly, D$_{\mathrm{C}}$ increases with dose rate in the low dose rate regime, likely due to the limited diffusion of ions. STEM-EELS spectrum imaging also revealed that damage occurs even in areas untouched by the beam. Altogether, our results suggest that although local heating can be important, other factors such as the dose rate must also be tuned to minimize beam damage. [Preview Abstract] |
Monday, March 13, 2017 1:27PM - 1:39PM |
B9.00010: Material sensitive grazing incidence small angle x-ray scattering Mihael Coric, Nitin Saxena, Jan Wernecke, Stefanie Langner, Peter Mueller-Buschbaum, Michael Krumrey, Eva M. Herzig We combine the structural analysis GISAXS (Grazing Incidence Small Angle X-ray Scattering) with the material sensitivity of spectroscopy. At resonant energy edges there is a drastic change in the absorption as well as in the dispersion behavior of the material containing the resonant atom. This causes variations in the scattering strength, generating sensitivity to the absorbing element. This approach has been successfully applied at the Carbon 1s absorption edge, an atom present in large amounts in every organic molecule.\footnote{Wang, C. et al.; \textbf{Nano Lett.} 2011, 11, (9), 3906-3911} We show an approach to exploit the weak changes in scattering strength due to a much lower concentration of atoms, e.g. sulfur, hence gaining material sensitivity in organic thin film materials. Using a model system, we are able to demonstrate that we can resolve the origin of scattering contrast in organic binary thin films using GISAXS measurements by varying the x-ray energy used during the experiment while at the same time obtaining information on structural length scales. [Preview Abstract] |
Monday, March 13, 2017 1:39PM - 1:51PM |
B9.00011: Control of Porosity in Ladder Polymers by Solvent-induced Aggregation. Michael Brady, Eri Gamo, Cheng Wang, Yan Xia Porous polymers hold promise as materials for gas absorption, membranes, and organic electronics. In all of these applications, attaining in-plane ordering of backbones and thus porous free volume impacts the ability to adsorb gas, selectively filter molecules, and conduct charges. In this work, hard and soft x-ray scattering and soft x-ray spectroscopy are of focus to study the pore structure, induced by the solution-driven aggregation of ladder polymer thin films made of LP-1 and LP-2. Using GISAXS and AFM it is shown that thermal annealing drives the growth of crystallites in thin films. Due to the completely \textit{sp2 }nature of the ladder polymer backbones, it is expected that backbones are extremely stiff and thus preventing them from packing once left in a metastable state following casting. Therefore, the combination of GIWAXS and GISAXS will be shown to be critical in correctly understanding how pores develop in this \textasciitilde 700 m2/g sorbent (N2). Finally, application in CO2/N2 separation membranes towards carbon sequestration will be presented that show gas selectivity is achieved through heteroatom incorporation and polymer blending. In this talk, focus will be placed on state-of-the-art x-ray scattering and spectroscopy, highlighting the importance of chemically sensitive structural information enabled by the combination of spectroscopy and scattering at play with the use of resonant soft x-rays. [Preview Abstract] |
Monday, March 13, 2017 1:51PM - 2:03PM |
B9.00012: Resonant Soft X-ray Scattering of Cellulose Microstructure in Plant Primary Cell Walls Dan Ye, Sarah N. Kiemle, Cheng Wang, Daniel J. Cosgrove, Esther W. Gomez, Enrique D. Gomez Cellulosic biomass is the most abundant raw material available for the production of renewable and sustainable biofuels. Breaking down cellulose is the rate-limiting step in economical biofuel production; therefore, a detailed understanding of the microscopic structure of plant cell walls is required to develop efficient biofuel conversion methods. Primary cell walls are key determinants of plant growth and mechanics. Their structure is complex and heterogeneous, making it difficult to elucidate how various components such as pectin, hemicellulose, and cellulose contribute to the overall structure. The electron density of these wall components is similar; such that conventional hard X-ray scattering does not generate enough contrast to resolve the different elements of the polysaccharide network. The chemical specificity of resonant soft X-ray scattering allows contrast to be generated based on differences in chemistry of the different polysaccharides. By varying incident X-ray energies, we have achieved increased scattering contrast between cellulose and other polysaccharides from primary cell walls of onions. By performing scattering at certain energies, features of the network structure of the cell wall are resolved. From the soft X-ray scattering results, we obtained the packing distance of cellulose microfibrils embedded in the polysaccharide network. [Preview Abstract] |
Monday, March 13, 2017 2:03PM - 2:15PM |
B9.00013: Strategies for Multi-Modal Analysis Alexander Hexemer, Cheng Wang, Ronald Pandolfi, Dinesh Kumar, Singanallur Venkatakrishnan, James Sethian This section on soft materials will be dedicated to discuss the extraction of the chemical distribution and spatial arrangement of constituent elements and functional groups at multiple length scales and, thus, the examination of collective dynamics, transport, and electronic ordering phenomena. Traditional measures of structure in soft materials have relied heavily on scattering and imaging based techniques due to their capacity to measure nanoscale dimensions and their capacity to monitor structure under conditions of dynamic stress loading. Special attentions are planned to focus on the application of resonant x-ray scattering, contrast-varied neutron scattering, analytical transmission electron microscopy, and their combinations. This session aims to bring experts in both scattering and electron microscope fields to discuss recent advances in selectively characterizing structural architectures of complex soft materials, which have often multi-components with a wide range of length scales and multiple functionalities, and thus hopes to foster novel ideas to decipher a higher level of structural complexity in soft materials in future. [Preview Abstract] |
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