Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session C46: Advanced Morphological Characterization of Polymeric Materials I: Soft and Hard X-ray, and Neutron ScatteringFocus
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Sponsoring Units: DPOLY Chair: Xiaodan Gu, Univ of Southern Mississippi Room: LACC 506 |
Monday, March 5, 2018 2:30PM - 2:42PM |
C46.00001: Exploring Structure and Chemistry of Soft Matter with X-ray Absorption Spectroscopy and Resonant Scattering Gregory Su, Isvar Cordova, Liwen Wan, Christopher Mcguirk, Jeffrey Long, David Prendergast, Walter Drisdell, Cheng Wang Continued progress in the development and performance of soft matter-based technologies depends critically on the ability to characterize chemistry and morphology in these systems. Energy tunable X-rays provide the ability to probe chemistry and structure through both X-ray absorption spectroscopy and scattering techniques. Here, we show how spectroscopy and scattering in the soft and tender X-ray regimes coupled with first-principles calculations can be applied to various soft matter systems, for example, gas adsorption mechanisms in amine-functionalized metal organic frameworks, morphology of hydrated vs. dry perfluorinated sulfonic-acid ionomer membrane materials, and orientation in semiconducting polymers. These findings highlight the need for continued development in combining theory and experiment to understand soft matter especially as studies move toward advanced in situ, operando, and time-resolved characterization. |
Monday, March 5, 2018 2:42PM - 2:54PM |
C46.00002: Resonant soft X-ray scattering study of fluidic phases with no electron density modulation Chenhui Zhu, Miroslaw Salamonczyk, Natasa Vaupotic, Damian Pociecha, Cheng Wang, Ewa Gorecka We have demonstrated that, when operated at carbon K-edge, the linearly polarized soft X-rays can enable bond orientation sensitivity, which can be utilized to probe the otherwise forbidden peak from the helices of twist bend nematic [2], B4 helical nanofilament phase [1], and cholesterol phase. Here we show that the same principle can be used to probe blue phase [3]. Furthermore, we discuss the relationship between the incoming linearly polarized X-rays, and the anisotropy in the scattering pattern. Future direction will be discussed as well [1] C. Zhu, et al. Nano. Lett. 15, 3420 (2015). [2]. C. Zhu, et al. Phys. Rev. Lett., 116, 147803 (2016). [3] M. Salamonczyk, et al. Soft Matter, (2017) |
Monday, March 5, 2018 2:54PM - 3:06PM |
C46.00003: Soft matter structure measurement by Polarized Resonant Soft X-ray Scattering Dean DeLongchamp In many applications of soft matter, the connection between structure and performance is complex, and conventional structure measurements are not sufficient to provide a predictive picture. Nanoscale variations in molecular orientation and composition, particularly in amorphous regions, are thought to be critical, but few techniques can probe them. I will describe our approach to polarized resonant soft X-ray scattering (P-RSoXS), 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. Progress and designs for a new P-RSOXS beamline will be shown. Results from model systems including commodity plastics, block copolymers, and organic photovoltaics blends will be discussed. |
Monday, March 5, 2018 3:06PM - 3:42PM |
C46.00004: Multimodal resonant x-ray scattering for polymer materials Invited Speaker: Cheng Wang An improved understanding of fundamental chemistry, morphology, and dynamics in polymers and soft materials requires advanced characterization techniques that amenable to in situ and in operando studies. Soft X-ray methods are especially useful in their ability to non-destructively provide material or chemical moiety specific information. Recent development of resonant soft x-ray scattering (RSoXS) at the Advanced Light Source (ALS) has enabled its applications to many critical research areas of materials research. Combining conventional x-ray scattering with soft x-ray absorption spectroscopy, RSoXS is a unique chemical sensitive structure probe that provides a novel route to unambiguously decipher the complex morphologies of mesoscale materials. Tuning x-ray photon energies to match the absorption spectrum of the different chemical components, the scattering contributions from the different components can be selectively enhanced, enabling a glimpse into these complex morphologies with unprecedented details. Applications of RSoXS have been extended to the areas of structured polymer assemblies, organic electronics, functional nano-composites, as well as liquid crystals. Recent development of customized instrumentation, multimodal characterization methods, as well as complementary theory and modeling for the extraction of the chemical distribution and spatial arrangement at multiple length scales in the application of polymer materials will be discussed. |
Monday, March 5, 2018 3:42PM - 3:54PM |
C46.00005: Improving Optical Models of Polarized R-SoXS for Quantitative Measurement of Molecular Orientation within Polymer Nanostructures Victor Murcia, Brian Collins Polarized R-SoXS is sensitive to local molecular orientation between domains within nanostructures, but it is difficult to interpret the data due to a lack of appropriate optical models. Uniaxial optical models are typically used in both NEXAFS and ellipsometry measurements of polymer films to determine molecular orientation with respect to a substrate. The model is based on transition dipole moments (TDM’s) being aligned either parallel or perpendicular to a primary molecular axis with respect to the incident electric field. We have successfully used this model in polarized R-SoXS to go beyond global orientation to measure correlative local molecular orientation with respect to interfaces. We show how this model can break down due to TDMs in the molecule that break uniaxial symmetry and detail an optical model free of this restriction that combines R-SoXS with DFT calculations. By correlating measured and calculated features we identify resonances with molecular moieties and assign separate TDM orientations. We show how this lower symmetry model may enable further details of molecular orientation to be extracted from complex polymer nanostructures. |
Monday, March 5, 2018 3:54PM - 4:06PM |
C46.00006: In-situ Resonant Soft X-ray Scattering Elucidates Crystalline-Amorphous Interfaces in Semicrystalline Polymers Eliot Gann, Tyler Martin, Subhrangsu Mukherjee, R. Joseph Kline, Lars Thomsen, Ronald Jones, Chad Snyder, Dean DeLongchamp Resonant Soft X-ray Scattering (RSoXS) reveals spatial correlations of molecular orientation in addition to correlations between chemical species within complex organic thin-films. In polyethylene films (both dry and in solvent), polarization induced RSoXS scattering anisotropy reveals the nature and extent of the molecular orientation between the lamellar crystalline domains. The crystalline-amorphous interface and the connectivity between the crystal layers within these materials is of particular interest for understanding and predicting materials behavior. Near Edge X-ray Fine Structure (NEXAFS) spectroscopy measures the complex angle-dependent resonant refractive index, which enables us to predict spectroscopic scattering patterns from different morphologies, and understand the experimental data. Of wide interest to the field, we characterize these systems in environmental cells, in which we have used several solvents including water. This capability is applicable to soft matter solid-liquid systems where chemical-specific molecular orientation and phase segregation is of interest. |
Monday, March 5, 2018 4:06PM - 4:18PM |
C46.00007: X-ray Photon Correlation Spectroscopy in Linear Diblock Copolymer Melts Ronald Lewis, Grayson Jackson, Michael Maher, Kyungtae Kim, Suresh Narayanan, Mahesh Mahanthappa, Frank Bates The specific dynamic processes which govern ordering in diblock copolymer melts are still largely unknown. Techniques such as Time-Resolved Small Angle X-ray Scattering and Rheology have been used in the past to characterize ordering kinetics, but these techniques generally lack the capability to decouple individual characteristic timescales of the system. To this end, we have employed X-ray Photon Correlation Spectroscopy (XPCS), a relatively new technique in soft materials, to further understand the kinetic mechanisms for ordering in linear diblock copolymers. Specifically, a series of model diblock copolymers with varying chemistry, composition, and molecular weight were investigated at several temperatures. The conclusions of this work are two-fold: i) XPCS is a feasible technique for measuring characteristic timescales of diblock copolymers, and ii) ordered diblock copolymers exhibit unique heterodyne mixing behavior under specific conditions. This work motivates additional XPCS studies to further elucidate the dynamics of ordering in diblock copolymer melts, as well as other related soft material systems. |
Monday, March 5, 2018 4:18PM - 4:30PM |
C46.00008: Strain Hardening and Morphological Evolution in Acid-Containing Polyethylenes via 2D Quantitative Fitting of In Situ X-ray Scattering During Tensile Deformation Karen Winey, Edward Trigg, L. Robert Middleton Some types of precise polyethylenes, or linear polyethylenes containing precisely periodic functional groups, can exhibit massive strain hardening under tensile deformation. Precise polyethylenes with pendant carboxylic acid groups exhibit strain hardening, while those with imidazolium bromide groups do not. To examine the mechanisms of deformation and evaluate the differences in tensile behavior with respect to morphological evolution, we perform in situ X-ray scattering during tensile deformation. Quantitative evaluation of the 2D fiber patterns show that the carboxylic acid polyethylene undergoes a drastic morphological transition, from a semicrystalline structure to a fibrillar structure, while the morphology of the imidazolium bromide polyethylene simply reorients without undergoing a significant change. This suggests that the fibrillization plays an important role in the strain hardening mechanism. |
Monday, March 5, 2018 4:30PM - 4:42PM |
C46.00009: Mapping Structural Evolution of Semi-crystalline Polymers to SAXS Patterns: An Explanation of the Butterfly Pattern William Kennedy, Hilmar Koerner, David Grubb, Sanjeeva Murthy Coupling the micromechanical behavior of semi-crystalline polymers under various processing conditions to the morphological and structural evolution of crystalline/amorphous regions has been the subject of study for decades. However, even with a wealth of experimental data via Small Angle X-ray Scattering (SAXS) there is currently no clear understanding of the underlying structural features that give rise to the observed scattering patterns, even less so describing the associated morphology evolution during transformation from one type of pattern to another. A unique type of SAXS pattern, commonly referred to as butterfly pattern, has been observed since the first SAXS studies on polymers, but has not been satisfactorily explained. In this presentation we model the morphologies, simulate the experimental SAXS data, and refine the model using key morphological parameters to fully explain the observed patterns in terms of chain slip and lamellar shear as the essential deformation modes. Not only does this approach illustrate the static SAXS pattern, it also reveals the transformation from e.g., a butterfly pattern to a simple 4-point pattern, often observed in semi-crystalline polymer processing. |
Monday, March 5, 2018 4:42PM - 4:54PM |
C46.00010: Characterization of cellulose microfibril crystal orientation in primary cell walls using X-ray scattering Dan Ye, Sintu Rongpipi, Sarah Kiemle, Chenhui Zhu, Daniel Cosgrove, Esther Gomez, Enrique Gomez Cellulose, one of the key components in plant cell walls, holds promise as a renewable source for biofuel production. In plant cell walls, cellulose is assembled into fibrils that are 3-5 nm in diameter and several hundred microns long. These cellulose microfibrils are stiff and are the load bearing component in plant cell walls. Nevertheless, many aspects of cellulose microfibril organization remain unknown, such as the orientation of cellulose crystals within fibrils. We have used grazing-incidence wide angle X-ray scattering to measure the distribution of cellulose crystal orientations with respect to the plant cell wall. Taking advantage of the high-flux X-ray source at synchrotron facilities and grazing incidence geometry, we generated pole figures to systematically study a series of primary cell walls. Samples were treated with different chemicals and enzymes to remove various components of the cell wall. Our results demonstrate that crystals within cellulose microfibrils in the plant cell wall have a preferred orientation, and that the degree of orientational order (texturing) varies depending on the plant species and type of tissue in a way not currently possible to reveal with other techniques. |
Monday, March 5, 2018 4:54PM - 5:06PM |
C46.00011: Thin film characterization using Grazing Incidence X-ray Scattering and Spectroscopy Mihael Coric, Nitin Saxena, Mika Pflüger, Peter Müller-Buschbaum, Michael Krumrey, Eva M. Herzig The nanostructure of organic thin films is often closely linked with its physical properties. Particularly for functional material systems, the interest is strong to be able to fully and unambiguously characterize the nanostructure of the surface and bulk of the films. We present here recent measurements using a combination of grazing incidence X-ray scattering (GIXS) and spectroscopy to investigate the nanomorphology of thin films applicable for a wide range of materials. |
Monday, March 5, 2018 5:06PM - 5:18PM |
C46.00012: Multiple Metastable Micellar States in Disordered Diblock Copolymers Kyungtae Kim, Akash Arora, Ronald Lewis, Meijiao Liu, Wei-hua Li, Anchang Shi, Kevin Dorfman, Frank Bates Low molar mass and compositionally asymmetric polyisoprene-b-polylactide (PI-PLA) diblock copolymers were ordered into multiple crystalline states, including BCC and the σ, C14, and C15 Frank-Kasper phases, using recently discovered thermal processing techniques. For a given pre-ordered phase, heating above the order-disorder transition temperature (TODT) followed by cooling below TODT returns the system to the same ordered state. Small angle x-ray scattering revealed that the number density of micellar particles, n/V, is retained in the highly structured disordered liquid. We hypothesize that the number of micelles per volume, n/V, imprinted on the liquid during the initial ordering stage, governs the symmetry breaking during subsequent crystallization, and that the metastable structured liquid cannot achieve the equilibrium particle density due to prohibitively large free-energy barriers for micelle fusion and fission. Once the n/V is fixed, facile chain exchange redistributes mass to meet the required particle sizes and packing associated with individual ordered phases. This work reveals the nature of the fluctuating disordered state in asymmetric diblock copolymers in the low molar mass limit. |
Monday, March 5, 2018 5:18PM - 5:30PM |
C46.00013: Interrogating the Network Structure in Crosslinked Polymer Networks via Neutron Porosimetry Bradley Frieberg, Christopher Stafford, Edwin Chan, Christopher Soles Many technologies and industries are dependent on the use of highly crosslinked polymer networks. These industries can range from coatings to water filtration to pharmaceuticals. The nature of the crosslinks can vary from covalent crosslinks to physical entanglements or hydrogen bonded networks. One key factor in understanding how these materials will function is a deeper understanding of their network structure over a variety of length scales. For example, in water filtration and desalination, highly crosslinked polyamides are often used. The function of the membrane and mechanism of filtration is directly related to pore or mesh size of the network. We have used a vapor flow cell to perform small-angle neutron scattering (SANS) porosimetry on crosslinked polymer networks. Information about the crosslink density, mesh size and the interaction between the solvent and polymer can be determined by swelling the network in-situ. Using SANS, we can probe the length scales that are relevant to the crosslink structure (nm to 100s of nm), as well as taking advantage of contrast match solvents to estimate a distribution in mesh sizes found within the network. |
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