Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session A52: Advanced Morphological Characterization of Polymers I: ImagingFocus
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Sponsoring Units: DPOLY Chair: Xiaodan Gu, University of Southern Mississippi Room: BCEC 253B |
Monday, March 4, 2019 8:00AM - 8:12AM |
A52.00001: Topological Defects in Tubular Network Block Copolymers Edwin Thomas, Hua Guo, Xueyan Feng Materials based on the double gyroid multicontinuous tubular structure can exhibit an array of exotic properties due to the unique 3D network structure. The nature, frequency and potential influence of topological defects present in the interpenetrating gyroid networks on various physical properties is an open question. We examined a polystyrene – polydimethylsiloxane copolymer possessing the double gyroid microdomain morphology in order to identify the types of topological defects present in high fidelity 3D reconstructions made by slice and view scanning electron microcopy tomography. Large volume tomograms were made by repeated sequentially ion beam milling of a thin section and then using a normal incidence electron beam to image the sample surface. We found node functionality “f defects” where the normal node functionality of 3 rose to 4 and to 5, broken network struts, bridging struts linking the two different networks as well as donut loops comprised of 5 or 6 node rings instead of the characteristic 10 node ring of the (10,3)-a gyroid network. We term the 5 node donut loops as 5-4,3 and 5-4,4,3 defects while the 6 node donut loop is termed a 6-4,3,4 defect to indicate, following Wells, the number of struts in the loop as well as the node functionality and sequence. |
Monday, March 4, 2019 8:12AM - 8:24AM |
A52.00002: Imaging and Engineering Polypeptoid Nanosheets with Atomic Scale Precision Xi Jiang, Sunting Xuan, Ryan Spencer, David Prendergast, Ronald Zuckermann, Nitash Balsara Imaging soft materials with atomic resolution using electron microscopy 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. Our experiments were conducted on crystalline nanosheets formed by self-assembly of amphiphilic polypeptoid molecules in water. Low-dose cryo-electron microscopy micrographs were obtained from frozen hydrated crystalline nanosheets. A combination of crystallographic and single particle methods, developed for cryo-electron microscopy of biological macromolecules, was used to obtain high resolution images of the crystals. Our approach is robust and enable direct visualization of the arrangement of bromine atoms in crystalline polypeptoid nanosheets. It also enables the engineering of polypeptoid nanostructures with atomic scale precision. |
Monday, March 4, 2019 8:24AM - 8:36AM |
A52.00003: Anatomical studies of ordered block copolymer bicontinuous networks via slice-and-view SEM reconstruction Christopher Burke, Xueyan Feng, Ishan Prasad, Edwin Thomas, Gregory Grason Slice and view scanning electron microscopy (SVSEM) is an imaging technique in which the surface of a sample is imaged via SEM and then an ion beam is used to mill away a thin slice, exposing a new surface for imaging. Here we demonstrate that in block copolymer (BCP) samples exhibiting the complex tubular network double gyroid phase, SVSEM provides high resolution images of large volumes, giving access to high quality geometric information. 3D Fourier analysis of the volume images gives reciprocal space information directly without the need for scattering experiments. Using a fitting technique we identify the reciprocal lattice vectors, which gives unit cell dimensions and symmetry information. We create skeletal graphs of the gyroid networks, one-dimensional reductions of the networks consisting of bonds and nodes that capture their topology and geometry. Inter-material dividing surfaces (IMDS) are constructed; we measure the mean and Gaussian curvature distribution on the surface and compare to theoretical predictions. Finally we calculate distances between the skeletal graph and the IMDS, and the IMDS and the gyroid minimal surface, providing a measure of the degree of packing frustration in the minority and majority phase domains. |
Monday, March 4, 2019 8:36AM - 8:48AM |
A52.00004: Minimizing beam damage with antioxidants to enable high resolution imaging of conjugated polymers in the electron microscope Brooke Kuei, Chengyu Song, Jim Ciston, 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), 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 addition of antioxidants. 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 the main mechanism for beam damage in conjugated polymers is diffusion of free radicals. Thus, we show with both Dc experiments and high-resolution TEM that the addition of free radical scavengers such as butylated hydroxytoluene (BHT) mitigates beam damage at room temperature. |
Monday, March 4, 2019 8:48AM - 9:00AM |
A52.00005: Three-dimensional morphological analysis of polymer blends through combined ToF-SIMS/AFM Hao Mei, Adeline Mah, Travis Laws, Wei Li, Tanguy Terlier, Rajeev Kumar, Gila E Stein, Rafael Verduzco Time-of-flight secondary ion mass spectroscopy (ToF-SIMS) enables three-dimensional compositional analysis using a focused ion beam along with an argon cluster beam for depth profiling. Combined with atomic force microscopy (AFM), topographical and compositional information can be acquired simultaneously. We apply ToF-SIMS to study the phase behavior of blends of bottlebrush polymers with linear polymers and generate a phase diagram for interfacial segregation. We quantify the composition of bottlebrush throughout the film by calibration of ion intensity ratios, and self-consistent field theory calculations elucidate the enthalpic and entropic contributions to segregation. We further analyze the three-dimensional morphology of phase-separation in thin film polymer blends using combined ToF-SIMS/AFM. ToF-SIMS/AFM is a powerful technique that enables analysis of unlabeled polymer blends, composites, and self-assembling systems. |
Monday, March 4, 2019 9:00AM - 9:12AM |
A52.00006: STM Characterization of Metallic Graphene Nanoribbons Daniel J Rizzo, Gregory Veber, Jingwei Jiang, Christopher Bronner, Ting Chen, Steven G. Louie, Felix R Fischer, Michael F Crommie Graphene nanoribbons (GNRs) are narrow strips of graphene that can host a wide range of 1-dimensional phenomena, including non-trivial topology and magnetism. The advent of molecule-based bottom-up synthesis techniques has enabled GNR properties to be tuned via the precise placement of individual carbon atoms. Realization of robust metallicity in bottom-up GNRs, however, remains elusive. The ability to engineer the frontier band structure of GNRs via hybridization of topologically-protected interface states suggests a strategy for inducing GNR metallicity by symmetrizing the hopping between adjacent interface states. Using this approach we have realized metallic GNR superlattices that are gapless by virtue of the symmetric placement of π-radical states along the GNR backbone. Scanning tunneling microscopy and spectroscopy (STM/STS) performed in conjunction with first-principles calculations confirms that these GNR superlattices possess a non-zero density of states (DOS) through EF, a hallmark of metallicity. Strategies for increasing the bandwidth of metallic GNRs will be discussed. |
Monday, March 4, 2019 9:12AM - 9:24AM |
A52.00007: nano-FTIR nanoscopy based identification of polymers at the 10nm length scale Andreas Huber, Stefan Mastel, Tobias Gokus, Alexander Govyadinov Scattering-type Scanning Near-field Optical Microscopy (s-SNOM) employs the strong confinement of light at the apex of a sharp metallic AFM tip to create a nanoscale optical hot-spot. Analyzing the scattered light from the tip enables the extraction of the optical properties below the tip and yields nanoscale resolved images simultaneous to topography [1]. Recently, the technology has been advanced to enable FTIR-spectroscopy on the nanoscale (nano-FTIR) [2]. |
Monday, March 4, 2019 9:24AM - 9:36AM |
A52.00008: Morphological Characterization of Well-Ordered Nanonetwork Materials via Real- and Reciprocal- Space Imaging POTING CHIU, YuCheng Chien, Rong-Ming Ho The morphological evolution of network phases from templated electroless plating using block copolymer as a template was investigated as an exemplary system for the characterization of developing complex gyroid and diamond phases from self-assembly. By taking advantage of the nucleation and growth mechanism of templated electroless plating, network-structured Au could be successfully fabricated through the development of Au nanoparticle, tripod/tetrapod and branched tripods/tetrapods, finally network structure. Hence, the morphological evolution of each stage could be examined by combining real-space observation of transmission electron microscopy with reciprocal-space investigation using small-angle X-ray scattering. A simple approach for the fitting of the scattering results was established at which the fingerprint scattering profiles of the building block for network phases were fitted with the form factor of sphere (i.e., the nanoparticle) and the diffraction results of final morphology (i.e., the network phases) could be well addressed by combined scattering of the form and structure factors, revealing the difference between the curvatures of gyroid and diamond phases from self-assembly. |
Monday, March 4, 2019 9:36AM - 10:12AM |
A52.00009: Recent developments of morphological characterization in nano-composite materials by electron microscopy Invited Speaker: Hiroshi Jinnai In order to truly understand various interesting properties of soft materials, it is crucial to directly visualize their morphologies both in quiescent state and under deformation. The interfacial region between fillers and polymer matrix, the interphase regionfor short, is believed to be one of the key morphological elements in nanocomposite materials. Direct visualization of such interphase region has been a subject for many years. Although transmission electron microscopy (TEM) is a powerful tool to visualize nano-scale polymeric morphologies, however, because the interphase region consists of the same polymeric species as the matrix, it is invisible under TEM. Atomic force microscopy (AFM), on the other hand, clearly demonstrates regions with higher elastic modulus (than the matrix) around the fillers, indicating the existence of the interphase region. However, because the mechanical properties can be easily affected by the structures underneath the measurement points, the high elastic regions around the fillers may not truly reflect the interphase region. Thus, we used transmission electron tomography, a nano-scale three-dimensional (3D) visualization method, to investigate the internal 3D structure of rubber nano-composite at exactly the same placeas the AFM force measurements. In doing so, it became possible to accurately determine the interphase regions for the first time. |
Monday, March 4, 2019 10:12AM - 10:24AM |
A52.00010: Contruction of 3D Models From USAXS on Aggregate Structures Alex McGlasson, Andrew J Mulderig, Greg Beaucage, Kabir Rishi, Vikram K Kuppa An accurate 3D model of aggregate structures is desirable for comparison with TEM micrographs and as an input to computer simulations of aggregate transport and growth. For example, we have used such 3D models for polymer nanocomposites with carbon black and silica. Ultra-small angle X-ray scattering was coupled to a hierarchical scattering model, the unified scattering function, to obtain topological parameters that describe 9 average features of aggregates including details of the branched structure. A simple diffusion limited aggregation model was simulated and use to generate aggregates using two free parameters, the degree of aggregation, z, and the sticking probability, p [1]. USAXS measurements resulted in z for input to the simulation and the single parameter p was varied from 0 to 1 until a value that could reproduce the 8 remaining USAXS aggregate descriptors was found. The simulated average aggregates agreed well with TEM micrographs of the same samples. This approach can be used to depict complex morphological differences in ceramic oxide and carbon black aggregates and has the potential to be applied to a wide range of other aggregated materials. |
Monday, March 4, 2019 10:24AM - 10:36AM |
A52.00011: Self-Assembled Morphologies of Poly(styrene-b-1,4-butadiene) Confined within Cone-Shaped Templates Youngkeol Kim, takeshi higuchi, Sungyoul Hwang, Anchang Shi, Baohui Li, Hiroshi Jinnai, Kookheon Char Block copolymers (BCPs) self-assembled under nanoscale confinement have distinctive nanostructures, which do not appear in bulk state. Especially, depending on different dimensionality of confinement spaces, shape and morphology of block copolymers and their optical properties are affected. In this study, we report phase-separated morphologies of polystyrene-block-1,4-polybutadiene (PS-b-PB) confined in conical templates with various size, shape and surface properties. Based on experimental observation using transmissional electron microscopy (TEM) and theoretical calculation of simulated annealing method, we found that phase separation of PS-b-PB in the conical confinement system are competitively affected by three thermodynamic factors; (1), (2) the interfacial energy between two different block and surrounding environment (air and substrates) and (3) the entropic penalty associated with large curvature at the vertices of conical pores. In addition, 3D imaging of TEM tomography were also performed in an attempt to identify internal nanostructures of BCP thoroughly. |
Monday, March 4, 2019 10:36AM - 10:48AM |
A52.00012: The distinctive microstructures in bitumen and their indication of bitumen’s phase stability Xiaokong Yu, Nancy Burnham, Sergio Granados-Focil, Mingjiang Tao Bitumen, similar to some amorphous polymeric systems, display diverse microstructures that are related to bitumen’s bulk physical and rheological properties; yet the chemical-microstructural-mechanical relationships for bitumen have been very challenging to establish due to bitumen’s complicated molecular interactions. To tackle this challenge, we chose two pristine bitumen (i.e., ABD and AAD), separated them into their asphaltene and maltene fractions, and prepared derivative bitumen by remixing their corresponding asphaltenes and maltenes at different ratios. We studied the microstructures of the two pristine bitumen and their derivatives using atomic force microscopy (AFM), and their phase stability using differential scanning calorimetry and their rheology using dynamic shear rheometry. Our results suggest that AAD-based derivatives had phase separation; in contrast, ABD-based samples were phase stable. The difference in phase stability between the two groups of bitumen is largely relevant to the aggregation behavior of their respective asphaltene fraction that was measured via NMR. |
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