Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session F49: Advanced Morphological Characterization of Polymer III: Anomalous Soft X-ray ScatteringFocus
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Sponsoring Units: DPOLY Chair: Cheng Wang, Lawrence Berkeley Natl Lab Room: BCEC 252A |
Tuesday, March 5, 2019 11:15AM - 11:27AM |
F49.00001: Critical-Dimension Grazing-Incidence Small Angle X-Ray Scattering: Applications using Soft, Tender and Hard X-Rays Guillaume Freychet, Dinesh Kumar, Isvar Cordova, Ronald J Pandolfi, Patrick Naulleau, Cheng Wang, Alexander Hexemer As the lithographically manufactured nanostructures are shrinking in size, conventional techniques, such as microscopies (SEM, AFM) reach their resolution limits. We have developed a high performance Grazing Incidence SAXS simulation tool to reconstruct the in-depth profile highly ordered material such as line gratings [1]. |
Tuesday, March 5, 2019 11:27AM - 11:39AM |
F49.00002: Label-free measurement of core-shell Pluronic F127 Micelle nanostructure determined using in-situ Resonant Soft x-ray Scattering Terry McAfee, Isvar Cordova, Thomas Ferron, Cheng Wang, Brian Collins Micelles are key to many applications such as drug delivery, and their size, shape and internal molecular conformation are of critical importance to their performance. By having both hydrophobic and hydrophilic monomer groups, polymers like Pluronic F127 self-assymble into spherical core-shell structures called Micelles. However, confirming the structural parameters, in particular conformation, is difficult if not impossible to date. Here we demonstrate a novel technique capable of such measurements based on Resonant Soft X-ray Scattering (RSoXS), which is uniquely sensitive to bond orientation and capable of probing organic materials using their intrinsic chemical structure for contrast manipulation rather than laborious and potentially disruptive isotopic labeling that is required in techniques such as neutron scattering. Like electron microscopy, RSoXS requires a high vacuum environment. By adapting a Poseidon Protochips TEM holder for use at BL11.0.1.2 of the Advance Light Source, we show that RSoXS can now be performed in in-situ/operando environments, allowing sample structure and interactions to be measured in the same conditions/environment as the intended application. |
Tuesday, March 5, 2019 11:39AM - 11:51AM |
F49.00003: Correlating anisotropy in polarized resonant soft X-ray scattering of block copolymer active layers with organic photovoltaic device performance Joshua Litofsky, Enrique D Gomez The use of Resonant Soft X-ray Scattering (RSoXS) allows the study of domain spacing and molecular orientation of conjugated polymers in the active layer of organic photovoltaics through tuning of the X-ray energy and polarization. Using the conjugated block copolymer system of poly(3-hexylthiophene) with acceptor blocks poly(fluorene-alt-dithienylbenzothiadiazole), (PFTBT), poly(carbazole-alt-dithienylbenzothiadiazole) (PCDTBT), and poly(phenylene-alt-dithienylbenzothiadiazole) (PPDTBT), along with alkyl side chain-added analogs PFT6BT, PCT6BT, and PPT6BT, we can examine the effects that morphological changes have on electronic device performance. The addition of hexyl side chains to the acceptor blocks decrease the degree of molecular order, as measured by the scattering anisotropy from RSoXS. This anisotropy has been shown to define the strength of alignment of chains with respect to the block copolymer interface within nematic domains, and can be used to directly compare long-range order between polymers. Based on our early findings, we believe that suppression of the long-range order is directly related to lower fill factors and lower device efficiencies. Studies into the charge carrier mobilities and crystallinity support these findings across the polymer systems. |
Tuesday, March 5, 2019 11:51AM - 12:27PM |
F49.00004: Advanced characterization of molecular nanostructures and interfaces with resonant X-ray scattering Invited Speaker: Brian Collins Emergent properties within molecular materials are determined by their nanoscale ordering, in particular at interfaces. This has revealed a potential for their use in drug delivery, printable electronics, and bottom-up nano-assembly if their ordering can be controlled. A major roadblock is the lack of nanoprobes that can precisely characterize ordering within these delicate materials that contain light elements, 3D structures, and low crystallinity. I will discuss recent progress in developing a new class of measurements based on X-rays resonant with molecular transitions to enable quantitative characterization of molecular order. Resonant soft X-ray scattering (RSoXS) combines polarized spectroscopy with scattering, enabling sensitivity to bond type and orientation – similar to ellipsometry and RAMAN spectroscopy but with higher spatial resolution. Contrast variation can be achieved by tuning the photon energy – similar to deuteration in neutron scattering but without the need of laborious and disruptive chemical labelling. I will highlight our recent progress in developing quantitative RSoXS analyses for characterizing molecular interfaces as well as ordering within and between nanostructures. In particular, the ability of polarized RSoXS to measure local molecular orientation even in polydisperse 3D matrices is not possible with any other technique. I will also touch on our work in developing a new instrument to measure structural evolution of solvated nanoparticles and operando electrochemical processes. As RSoXS continues to mature, it will enable increased understanding and control of molecular and hybrid nanostructures resulting in revolutionary new technologies based on these novel materials. |
Tuesday, March 5, 2019 12:27PM - 12:39PM |
F49.00005: Probing Molecular Orientation using Polarized Resonant Soft X-ray Reflectivity Jacob Thelen, Camille Bishop, Daniel Sunday, Eliot H Gann, Mark Ediger, Dean DeLongchamp Charge transport in organic semiconducting films is inherently anisotropic: it depends on the orientation and packing of the molecules, which in turn are influenced by molecular structure and film processing conditions. A technique capable of non-destructively depth-profiling molecular orientation with (sub)nanometer-level depth resolution would enable a significant improvement in the understanding of structure-property-processing relationships in organic semiconductor devices. We explore the feasibility of using polarized resonant soft X-ray reflectivity (p-RSoXR) as a tool to profile molecular orientation by studying a model set of glassy small molecule (posaconazole) films with different net orientations. By comparison with variable angle spectroscopic ellipsometry (VASE) and near edge X-ray absorption fine structure (NEXAFS) data, we show that p-RSoXR is sensitive to both surface and bulk molecular orientation in the films. We conclude by demonstrating our approach to extracting orientation profiles from p-RSoXR data, as well as discussing the current strengths and limitations of the technique. |
Tuesday, March 5, 2019 12:39PM - 12:51PM |
F49.00006: Effects of Confinement on the Structure of Bottlebrush Polymers in Thin Films Daniel Sunday, Alice Chang, Moshe Dolejsi, Paul F Nealey, Robert H Grubbs, R. Joseph Kline Bottlebrush block copolymers (BCPs) have intriguing potential in nanopatterning and photonics applications as they lack entanglements and can rapidly assemble. As a result, bottlebrush BCPs can self-assemble with periodicities over 100 nm, a length scale which is challenging to achieve with linear BCPs. Nanopatterning applications will require confinement of bottlebrush BCPs in thin films, where their behavior is still poorly understood. The assembly of bottlebrush BCPs of polystyrene-b-poly(lactic acid) (PS-b-PLA) in thin films was studied using a combination of techniques. Blade coating was used to produce a controlled thickness gradient so that the impact of the thickness/periodicity ratio can be studied. The resulting structures were evaluated using a combination of atomic force microscopy (AFM), grazing incidence X-ray scattering (GISAXS) and resonant soft X-ray scattering (RSoXS). The effects of solvent and annealing conditions on the resulting morphologies was also explored. |
Tuesday, March 5, 2019 12:51PM - 1:03PM |
F49.00007: Improving Optical Models of Polarized R-SoXS for Quantitative Measurement of Molecular Orientation within Polymer Nanostructures Victor Murcia, Brian Collins Resonant soft X-ray scattering (RSoXS) with polarized X-rays is sensitive to local molecular orientation within nanostructures but it is difficult to interpret the scattering patterns due to a lack of appropriate optical models. Uniaxial optical tensors have been used successfully to measure average global molecular orientation in X-ray absorption spectroscopy (XAS) and ellipsometry. The model reduces into diagonal tensors whose elements correspond to parallel and perpendicular alignments of the incident electric field with respect to the transition dipole moment. It is uncertain, however, if such a model will work in polarized RSoXS as it assesses differences in local ordering. We show how to create such a model using XAS measurements and test it against polarized RSoXS measurements on pure films of a semicrystalline conjugated polymer. We show the model works for the pi* resonances but breaks down in regions that include other transitions. DFT calculations demonstrate how not all transitions follow uniaxial symmetry and require a lower symmetry model to reproduce measurements. Combining XAS and DFT into such a new model may enable further details of local molecular orientation to be extracted by pol-RSoXS that remove current limitations of XAS. |
Tuesday, March 5, 2019 1:03PM - 1:15PM |
F49.00008: Characterization of ion distribution around the surface of micelles under high salt conditions using small angle neutron scattering and resonant soft x-ray scattering Hanqiu Jiang, Greg Beaucage, Karsten Vogtt Surfactants can self-assemble into micelles once reaching critical micellar concentration. Industrially, high concentration of inorganic salts are frequently employed as additives for surfactant systems to depress the CMC of the system, enhance further growth of micelle and eventually alter the rheological behavior of targeted systems. Although frequently employed in commercial surfactant products and in biological systems, little was known about how ions behave around these aggregates under high salt condition. An ion cloud model was recently developed based on the screening effect observed in small angle neutron scattering for the high salt condition. To verify this model, resonant soft x-ray scattering was performed by setting the energy of the incident x-ray close to the absorption edge of Cl atom, which allows the manipulation of the scattering length density. The scattering contribution of the ion cloud layer can thus be obtained through the subtraction of scattering curves measured at different energies. This also allows verification of the forcefield and other protocols applied in micelle simulations and enhance the predictability of micelle behavior. |
Tuesday, March 5, 2019 1:15PM - 1:27PM |
F49.00009: ABSTRACT WITHDRAWN
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Tuesday, March 5, 2019 1:27PM - 1:39PM |
F49.00010: Elucidating microphase separation in perfluoropolyether triblock copolymers using scattering techniques Deep Shah, Kevin Olson, Xiuhong Li, Bruce Allen Garetz, Sue Mecham, Joseph M. DeSimone, Nitash Balsara Short chain perfluoropolyether (PFPE) polymers have recently been shown to conduct and solvate lithium salts, and thus can be used as homopolymer electrolytes for battery applications. In an attempt to improve the transport characteristics, poly(ethylene oxide) (PEO) has been covalently bonded to the ends of PFPEs to form triblock copolymers of type A-B-A. By increasing the lengths of the PEO segments, the segregation strength of the copolymers increases; at the highest PEO molecular weight, the copolymers microphase separate. While phase separation was not immediately apparent using small angle X-ray scattering (SAXS), measuring birefringence with depolarized light scattering (DPLS) allows for the conclusion of phase separation. The Flory-Huggins interaction parameter between PEO and PFPE was calculated to determine the segregation strength as a function of salt concentration. This work provides thermodynamic data on the interactions between non-fluorinated end-groups and fluorinated backbones. |
Tuesday, March 5, 2019 1:39PM - 1:51PM |
F49.00011: Stability of Complex Spherical Packing Phases in Low-Molecular-Weight Diblock Copolymers Jiayu Xie, Chi To Lai, Anchang Shi Block copolymers are known for their ability to self-assemble into an array of ordered structures. Of special interest are the spherical packing phases due to their similarity to the atomic crystals. Until the past decade, the packing arrangement was believed to be primarily body-centered cubic for diblock copolymers. However, recent experimental and theoretical studies have revealed the emergence of various complex spherical phases including the Frank-Kasper phases. Qualitatively, the agreement between experimental and theoretical phase behaviour of diblocks is remarkable. On the other hand, quantitative differences still exist. These discrepancies could be due to numerous factors, such as polydispersity and the non-Gaussian nature of low-molecular-weight polymers used in experiments. In this work, we examine the formation of complex spherical phases for low-molecular-weight polymers with conformational asymmetry. Using the self-consistent field theory applied to freely-joint polymer chains, we model the conformational asymmetry by a difference in the bond lengths of the A and B blocks. Our results indicate that, consistent with the experiments, the inclusion of polydispersity and short-chain statistics leads to a shift of the phase boundaries between different ordered phases. |
Tuesday, March 5, 2019 1:51PM - 2:03PM |
F49.00012: Effect of Free-Volume Holes on Dynamic Mechanical Properties of Epoxy Resins for Carbon-Fiber-Reinforced Polymers Studied by Positron Annihilation Hongjun Zhang, Selvakuma Sellaiyan, T. Kakizaki, Akira Uedono, Y. Taniguchi, K. Hayashi We studied the effect of free-volume holes on dynamic mechanical properties (storage modulus E', loss modulus E'', damping factor tanδ, and complex viscosity |η*|) for six types of amine-cured epoxy resins with different chemical structures. Positron annihilation lifetime (PAL) experiments were applied to determine the free-volume hole properties of each sample. The correlations between hole fraction and dynamic mechanical parameters were studied by Williams-Landel-Ferry equation. In the temperature range of Tg(PAL)<T<Tg(PAL)+100 °C (Tg(PAL) is the Tg given by PAL experiments), regular variations of dynamic mechanical parameters with increasing relative hole fraction (1-hPAL@Tr/hPAL, where hPAL is the hole fraction from PAL experiments, and hPAL@Tr is the hPAL at reference temperature Tr) are revealed: (1) log[E'(T)] and log[|η*|(T)] initially decrease linearly and then remain nearly unchanged; (2) log[E''(T)] and log[tanδ(T)] initially increases linearly and then decrease linearly. In this work, PAL spectroscopy provided precious quantitative information of free-volume holes in polymers [1]. |
Tuesday, March 5, 2019 2:03PM - 2:15PM |
F49.00013: Effect of temperature on thermal conductivity of aligned amorphous polyethylene - Molecular Dynamics study Rajmohan Muthaiah, Jivtesh Garg The effects of temperature dependence of the thermal conductivity (k) of chain-oriented amorphous polyethylene (PE) using Molecular Dynamics Simulation. We found that the temperature corresponding to a peak k progressively decreases by increasing the levels of orientation. Un-oriented PE exhibits the peak k at 350K, while aligned PE under an applied strain of 400% shows a maximum at 100K. This transition of peak k to lower temperatures with increasing alignment is explained in terms of a crossover from disorder to anharmonicity dominated phonon transport in aligned polymers. The disorder in the polymer chain is manipulated to support this crossover corresponding to peak k. Disorder is controlled through a change in the dihedral parameters of the potential function, allowing a change in the relative fraction of trans and gauche transformations. The results shed light on the underlying thermal transport processes in aligned polymers and hold importance for low temperature applications of polymer materials in thermal management technologies. |
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