Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session F9: Multimodal Characterization of Soft Materials in Complex Environments IIFocus
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Sponsoring Units: DPOLY Chair: Matthew Tirrell, University of Chicago Room: 268 |
Tuesday, March 14, 2017 11:15AM - 11:51AM |
F9.00001: Three dimensional characterization of polymer nanostructures through an integrated scattering and modeling approach Invited Speaker: Manolis Doxastakis Modern scattering techniques such as resonant X-ray and grazing-incidence small-angle X-ray scattering offer an unprecedented ability to quantitatively characterize nanoscale polymer structures on a substrate or embedded within thin films. In the case of line gratings or polymer lamellae formed by directed-self assembly, if the long structures are arranged with a nanoscale periodicity perpendicular to the beam, then scattering is concentrated into a series of characteristic spots recorded on a two-dimensional detector. The intensity of these spots is modulated by the three-dimensional shape and arrangement of the lines. However, data analysis is often focused onto extracting a two-dimensional model for the sample cross-section, discarding any additional information that the measurements can provide. In this talk, we will discuss how to leverage methods to extract details on the three-dimensional structure of such soft materials using a concerted computational and experimental approach. We will demonstrate the necessity to implement an efficient modeling strategy that maximizes output from such state-of-the art experimental techniques. Furthermore, by coupling molecular simulations to scattering we provide estimates on the thermodynamic and kinetic factors driving structure formation that are otherwise inaccessible. This combined modeling and scattering method is critical to probe and control processes central in the development of the next generation materials in nanopatterning. [Preview Abstract] |
Tuesday, March 14, 2017 11:51AM - 12:03PM |
F9.00002: Three-Dimensional Characterization of Block Copolymers using Molecular Simulation and Small-Angle X-ray Scattering Alec Bowen, Manolis Doxastakis, Gurdaman Khaira, Paul Nealey, Juan de Pablo Block copolymers have gained considerable interest for their ability to spontaneously form vast arrays of nanoscale structures, which is of particular use in semiconductor manufacturing and membrane fuel cell applications. However, these materials typically rely on precise substrate patterns and composition control to form ideal structures. A fully three-dimensional characterization technique is necessary for understanding the relationship between thermodynamic process conditions and resultant nano-structures, and consequently fine-tuning them into their desired form. We present a new method that couples experimental small angle X-ray scattering techniques to detailed physics-based molecular simulation models to produce a powerful three-dimensional metrology for block-copolymer systems. As the method uses scattering techniques, it is able to provide statistical information over large regions, providing insight into long-range phenomena such as line edge roughness. We have used our simulation-based characterization technique on a variety of samples, all of which have shown excellent agreement with other, two-dimensional characterization techniques, such as scanning electron microscopy and atomic force microscopy. [Preview Abstract] |
Tuesday, March 14, 2017 12:03PM - 12:15PM |
F9.00003: Characterizing Molecular Orientation with Polarized Resonant Critical Dimension Small Angle X-Ray Scattering Christopher Liman, Daniel Sunday, Hyun Wook Ro, Lee Richter, Thom Germer, R. Joseph Kline Critical dimension small angle X-ray scattering is a recently developed variable angle transmission technique that enables the characterization of the three-dimensional shape of periodic nanostructures such as the buried interfaces of directed self-assembled block copolymer lamellae. By using this technique at resonant soft X-ray energies with different polarizations to analyze polymer nanostructures, we not only improve the scattering contrast but also gain information about the preferential molecular orientations of these nanostructures. The information about shape and molecular orientation is convolved in the scattering and must be extracted by comparing it to simulated scattering and fitting using an inverse iterative algorithm. We first compare simulated scattering generated using rigorous couple wave analysis and a simpler optical model, and address questions of fit uniqueness. We then test this technique on model systems of polymer nanogratings fabricated using replica molding and nanoimprint lithography. Carbon 1s-pi* transition energies are used to probe the biaxial orientation of the aromatic rings in the polymer backbones. Distinct asymmetry in the scattering pattern results from the interaction of the beam geometry and the change in orientation across a periodic repeat unit, improving fit uniqueness. Fits of the scattering are compared to results from spectroscopic ellipsometry. [Preview Abstract] |
Tuesday, March 14, 2017 12:15PM - 12:27PM |
F9.00004: Functional Group Depth Profiling with Resonant Soft X-ray Reflectivity Daniel Sunday, Edwin P. Chan, Sara V. Orski, Chris M. Stafford The distribution and concentration of functional groups in thin films can be difficult to characterize due to the small sample volume and limited methods with depth sensitivity beyond the film surface. Soft X-rays with energies in the vicinity of an atomic absorption edge are sensitive to specific chemical functionalities. In this contribution, we demonstrate how resonant soft x-ray reflectivity can be used to quantifying the distribution of specific functional groups in polyamide thin films, which have applications as water purification membranes. Using a layer-by-layer assembly system for the synthesis of the polyamide we can control the concentration of oxygen or nitrogen based functional groups within the thin film. Three different polyamide films were prepared with different precursor materials in order to control the functional group concentration in the film. The measurement was calibrated using a series of reference films composed of random copolymers with controlled copolymer compositions. The results of this measurement can be used to determine the cross-link density and residual hydroxyl group concentration, which can be related to the performance of the membrane. [Preview Abstract] |
Tuesday, March 14, 2017 12:27PM - 12:39PM |
F9.00005: Polarization effect in resonant soft X-ray scattering study of helical liquid crystal phases. Chenhui Zhu, Miroslaw Salamoncyzk, Anthony Young, Cheng Wang, Alexander Hexemer, Jim Gleeson, Antal Jakli, Sam Sprunt, Michael Tuchband, Min Shuai, Joseph Maclennan, David Walba, Noel Clark, Ewa Grecka, Damian Pociecha, Natasa Vaupotic Liquid crystals form many interesting nano-scale structures, many of which can be probed with X-ray scattering techniques, such as layering in smectics, hexagonal packing of cylinders in discotics. Typically hard X-rays are used due to its high penetrating power. However, in the hard X-ray regime, the scattering contrast of some LC nanostructures can be extremely low due to their weak electron density modulation. Here we show that by utilizing the coupling between x-ray polarization and molecular bond orientation, it is possible to use polarized soft x-rays at carbon resonant k-edge to probe helical strictures, i.e. the helical nanofilament B4 phase [1], the newly discovered twist bend nematic phase [2], and the blue phase [3], which are structures with no or minimal electron density modulation. Furthermore, we will discuss the relationship between the scattering anisotropy and the polarization of the incoming x-rays. These work show the great potential of resonant soft x-ray scattering in investigating structures of high orientational order. [Preview Abstract] |
Tuesday, March 14, 2017 12:39PM - 12:51PM |
F9.00006: Resonant Soft X-ray Scattering as a Powerful Probe of Buried Polymer Interfaces Wei Chen, Zhang Jiang, Matthew Tirrell Elucidation of polymer interfacial structures provides insights into interfacial molecular mechanisms for coating protection, adhesion, lubrication, friction, wettability, biocompatibility, and even charge transport properties. Resonant Soft X-ray Scattering (RSoXS) offers a unique element, site and valence specific probe to study spatial modulations of molecular orbital degrees of freedom on the nanoscopic length scale. This unique sensitivity is achieved by merging small angle x-ray scattering and x-ray absorption spectroscopy into a single experiment, where the scattering provides information about spatial modulations and the spectroscopy provides sensitivity to the molecular anisotropy. Here we applied RSoXS to polystyrene (PS) films at solid-solid interfaces and poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) brushes at solid-liquid interfaces. It is found that the interfacial width of PS thin film is about one order of magnitude large than those observed by traditional scattering techniques. In addition, although the ion-induced changes of PMPC thickness are not apparent in aqueous solutions, their chain conformations like polyzwitterion distribution and correlation varied, dependent on salt types, ionic strengths and ion valences. Consequently, it is evident that RSoXS is a powerful probe of buried polymer interlaces with both spatial and chemical sensitivities. [Preview Abstract] |
Tuesday, March 14, 2017 12:51PM - 1:03PM |
F9.00007: Chain Conformation of Phosphorycholine-based Zwitterionic Polymer Brushes in Aqueous Solutions Jun Mao, Jing Yu, Sungsik Lee, Guangcui Yuan, Sushil Satija, Wei Chen, Matthew Tirrell Polyzwitterionic brushes are resistant to nonspecific accumulation of proteins and microorganisms, making them excellent candidates for antifouling applications. It is well-known that polyzwitterions exhibit the so-called antipolyelectrolyte effect: Polyzwitterionic brushes would adopt a collapsed conformation at a low ionic strength due to the electrostatic inter/intra-chain association; whereas at a high ionic strength, they would exhibit an extended conformation because the electrostatic inter/intra-chain dipole–dipole interaction is weakened. However, poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) is a unique member in polyzwitterionic families. Its ultrahigh affinity to water leads to no detectable shrinks in aqueous solutions even at low ionic strengths. In this study, we synthesized highly dense PMPC brushes via surface initiated radical polymerization and systematically investigate their conformational behaviors at solid-liquid interfaces in the presence of multivalent counterions, combining X-ray and neutron scattering and force measurements. We have demonstrated that despite no obvious changes of the entire lengths of extended PMPC brushes in aqueous solutions, the chain conformations including, but not limited to, polyzwitterion distribution and charge correlation, varied, dependent on salt types, ionic strengths and ion valences. [Preview Abstract] |
Tuesday, March 14, 2017 1:03PM - 1:15PM |
F9.00008: Resonant Soft X-Ray Scattering for the Multimodal Operando Characterization of Proton Exchange Membranes Isvar Cordova, Gregory Su, David Kilcoyne, Ahmet Kusoglu, Adam Weber, Cheng Wang The design of novel high-performance membranes for electrochemical applications relies on our ability to elucidate the relationships between their nanometer-scale chemistry, physical structure, and function. Our study harnesses the spatio-chemical sensitivity that is inherent to Resonant Soft X-ray Scattering (RSoXS) to characterize the proton exchange membrane component of a custom fuel/electrolytic cell under operando conditions, while also facilitating complementary studies with other spectromicroscopic methods. In this presentation, we will present recent results on Nafion, a membrane material that is considered to be a critical cost and performance-limiting component in many electrochemical devices. Recent RSoXS results acquired with a wet sample cell interrogated the Nafion films' partially orientated molecules inside ionomer domains. Using polarized X-rays tuned to the fluorine absorption edge, we observed a strong scattering anisotropy that indicated preferred local crystalline grain orientation at the interface between different phases. We will then expand on how combining such operando RSoXS data with other analytical methods can uncover important dynamic structure-property relationships underlying the interplay of various critical performance factors. [Preview Abstract] |
Tuesday, March 14, 2017 1:15PM - 1:27PM |
F9.00009: Gel Phase Formation in Dilute Triblock Copolyelectrolyte Complexes Samanvaya Srivastava, Marat Andreev, Vivek Prabhu, Juan de Pablo, Matthew Tirrell Assembly of oppositely charged triblock copolyelectrolytes into phase-separated gels at extremely low polymer concentrations (\textless 1 {\%} by mass) has been observed in scattering experiments and molecular dynamics simulations. In contrast to uncharged, amphiphilic block copolymers that form discrete micelles at low concentrations and enter a phase of strongly interacting micelles in a gradual manner with increasing polymer concentrations, the formation of a dilute phase of individual micelles is prevented in polyelectrolyte complexation-driven assemblies of triblock copolyelectrolytes. Gel phases form and phase separate almost instantaneously upon solvation of the copolymers. Furthermore, molecular models of self-assembly demonstrate the presence of oligo-chain aggregates in early stages of triblock copolyelectrolyte assembly, at experimentally unobservable polymer concentrations. Our discoveries not only contribute to our fundamental understanding of the structure and pathways of complexation driven assemblies, but also raise intriguing prospects for formation of gel structures at extraordinarily low concentrations, with applications in tissue engineering, agriculture, water purification and theranostics. [Preview Abstract] |
Tuesday, March 14, 2017 1:27PM - 1:39PM |
F9.00010: Experimentally Determined Polyelectrolyte Complexation Phase Diagrams Lu Li, Samanvaya Srivastava, Matthew Tirrell Polyelectrolyte complexation is the associative phase separation of oppositely charged macromolecules in aqueous environments, caused by the correlated electrostatic interactions among the chains and the entropy gains from release of the counterions associated with the chains. Understanding the phase compositions and small molecule partitioning during complexation are of vital importance in motivating development of complex-based materials for biomedical applications. Harnessing the availability of synthetic polyelectrolytes with controlled properties, we will present experimentally determined complexation phase diagrams for several low-polydispersity polymer systems with varying hydrophobic and electrostatic properties. Using meticulous measurements, we will demonstrate that while parts of the phase diagrams agree with the general trends predicted by traditional Voorn-Overbeek model, the contributions of polyelectrolyte backbone hydrophobicity become increasingly significant with increasing polymer as well as salt concentrations, leading to non-trivial deviations from the expected results. [Preview Abstract] |
Tuesday, March 14, 2017 1:39PM - 1:51PM |
F9.00011: Molecular Exchange Kinetics in Polyelectrolyte Complex Micelles Hao Wu, Samanvaya Srivastava, Jeff Ting, Matthew Tirrell Polyelectrolyte~complex (PEC) micelles form when oppositely charged block polyelectrolytes are mixed together in aqueous media. These nanoscale PEC micelles have varied biomedical applications including drug and gene delivery, tissue engineering and diagnostics. However, much less is known about the structural stability of the PEC micelles, particularly the mechanism fundamentally governing the molecular exchange kinetics between the micelles. We will present a systematic study of structural stability and molecular exchange kinetics in polyelectrolyte complex micelles (PECs) using dynamic light scattering, small-angle X-ray scattering (SAXS) and time-resolved small-angle neutron scattering (TR-SANS) as a function of various parameters, including core-forming block length, charge density, salt concentration and polymeric conformation. [Preview Abstract] |
Tuesday, March 14, 2017 1:51PM - 2:03PM |
F9.00012: Hierarchical structure and dynamics of oligocarbonate-functionalized PEG block copolymer gels Vivek Prabhu, Guangmin Wei, Samim Ali, Shrinivas Venkataraman, Yi Yan Yang, James Hedrick Hierarchical, self-assembled block copolymers in aqueous solutions provide advanced materials for biomaterial applications. Recent advancements in the synthesis of aliphatic polycarbonates have shown nontraditional micellar and hierarchical structures driven by the supramolecular assembly of the carbonate block functionality that includes cholesterol, vitamin D, and fluorene. This presentation shall describe the supramolecular assembly structure and dynamics observed by static and dynamic light scattering, small-angle neutron scattering and transmission electron microscopy in a model pi-pi stacking driven fluorene system. The combination of real-space and reciprocal space methods to develop appropriate models that quantify the structure from the micelle to transient gel network will be discussed. [Preview Abstract] |
Tuesday, March 14, 2017 2:03PM - 2:15PM |
F9.00013: Measuring Lithium Dendritic Growth in Polymer Electrolytes Yuping He, Gregory Downing, Howard Wang The nature of Li dendritic growth in polymeric electrolytes for rechargeable batteries has been investigated using simultaneous electrochemical and neutron depth profiling (NDP) measurements. A symmetric sandwich cell of Li / poly(ethyleneoxide) (PEO) : lithium bis(trifluoromethane)sulfonamide (LiTFSI) / Li was used as a model system in this study. Operating the cell at a constant electric current of 0.1 mA, in situ NDP measurements show that after a period of steady Li plating, dendrites start to grow, which eventually short-circuit the sandwich cell. 3D Li mapping reveals heterogeneous lateral distribution of Li over length scales from below a millimeter to centimeters. Most Li in the electrolyte layer resides in dendrites growing from the top electrode, it is observed that dendrites also grow from the bottom electrode, where presumably only Li oxidation reaction occurs. The revelation poses new design and engineering challenges in using Li metal electrode in future development of rechargeable batteries. [Preview Abstract] |
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