Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session H56: Advanced Morphological Characterization of Polymeric Materials II: Emerging Microscopy and Spectroscopy TechniquesFocus
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Sponsoring Units: DPOLY Chair: Brian Collins, Washington State Univ Room: LACC 515B |
Tuesday, March 6, 2018 2:30PM - 3:06PM |
H56.00001: Break - Dillon Medal Talk
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Tuesday, March 6, 2018 3:06PM - 3:42PM |
H56.00002: In-Situ Imaging of Polymer and Organic Molecular Materials by Transmission Electron Microscopy Invited Speaker: David Martin We have been examining the use of in-situ techniques for monitoring the oxidative electrochemical polymerization of conjugated polythiophenes such as poly(3,4-ethylene dioxythiophene) (PEDOT) using transmission electron microscopy (TEM). Our approach utilizes a thin (~500 nm) film of reactive EDOT monomer-containing liquid sandwiched between a bottom substrate with microfabricated working, reference, and counter electrodes; and a solid top film. The electron dose must be carefully controlled and monitored during imaging to avoid damage to the sample and artifacts such as bubble formation. The method allows for the direct visualization of the transition from liquid EDOT monomer, through viscoelastic oligomers, to the final solid PEDOT polymer product. The detailed size, shape, and distribution of the precipitating intermediate states can be resolved, revealing new information about the local mechanisms of electrodeposition. This includes the evaporation of previously formed droplets back into the solution, presumably by curvature-driven variations in solubility similar to Ostwald ripening. Complimentary information about the processes seen in TEM can be obtained by a variety of other techniques including optical microscopy, scanning electron microscopy, and spatially-resolved infrared and Raman spectroscopies. |
Tuesday, March 6, 2018 3:42PM - 3:54PM |
H56.00003: Minimizing beam damage with antioxidants to enable high resolution imaging of conjugated polymers in the electron microscope Brooke Kuei, Enrique 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. DC is also higher for polymers with higher Tg. Altogether, these results suggest that the main mechanism for beam damage in conjugated polymers is diffusion of free radicals. Thus, we show that the addition of free radical scavengers such as butylated hydroxytoluene (BHT) mitigates beam damage at room temperature. We predict that the addition of BHT is important to enable high-resolution experiments without cryogenic conditions. |
Tuesday, March 6, 2018 3:54PM - 4:06PM |
H56.00004: Electron Tomography Reveals Details of the Internal Microstructure of Desalination Membranes Tyler Culp, Yue-xiao Shen, Mou Paul, Abhishek Roy, Michael Behr, Steve Rosenberg, Manish Kumar, Enrique Gomez Reverse osmosis (RO) membranes are the most widely used technique for desalination and reuse of wastewater, treating tens of billions of gallons of water per day. However, the internal structure of fully-aromatic polyamide films used in RO is largely unknown. In this work, the internal structure of the active layer of RO membranes was investigated using scanning transmission electron microscopy (STEM) tomography. Quantitative analysis of the 3D models of the active layer of compressed commercial membrane samples revealed that internal voids account for less than 0.3% of the total polyamide volume, contrary to previous reports that report values that are two orders of magnitude higher. We also measured that the normalized surface area of the polyamide top surface to be 3.48 and 3.07 for the seawater desalination and brackish water desalination membranes examined, respectively. These surface area values are more than double of what the conventional technique, atomic force microscopy (AFM), reports for such measurements. The reported procedures for obtaining a high-resolution 3D model of aromatic polyamide membranes and the obtained structural information can be used for further studies which could inform development of the next generation of water purification membranes. |
Tuesday, March 6, 2018 4:06PM - 4:18PM |
H56.00005: An imaging platform for single-molecule super-resolution microscopy in organic polymer materials Muzhou Wang, Zhe Qiang, Kevin Shebek, Masahiro Irie Super-resolution microscopy offers an exciting method for direct in situ real-space observation at nanometer resolutions. Most previous studies have applied these techniques to important scientific problems in the biological community, but little work has explored their use in materials science. In this work, we develop a photoswitchable fluorophore optimized for organic environments, and we explore its incorporation into a super-resolution microscopy experiment. The fluorophore is polymerizable which greatly streamlines labeling strategies into a single step, where a small quantity is mixed with standard monomers and copolymerized to yield the functionalized material with no further purification. Nanoscale imaging is demonstrated through single-molecule super-resolution of polymer blends. Individual fluorophores can be switched several times between bright and dark states, enabling repeated time-lapse imaging. We hope this platform removes barriers from fluorophore chemistry, promoting widespread adoption of super-resolution microscopy in the polymer community. |
Tuesday, March 6, 2018 4:18PM - 4:30PM |
H56.00006: Environmental and Variable-Temperature Studies of Polymers with High-Speed AFM Sergei Magonov, Shijie Wu Atomic Force Microscopy (AFM) as the well-established technique for characterization of polymers is further advanced with high-speed scanning. Quick Scan in Keysight microscopes is realized with a fast response nose-cone, which is embedded into a regular scanner, and the use of high-frequency probes. This mode enables the scanning rates up to 100 Hz on areas from 100 nm to 100 μm. Quick scan operation can be carried out in different organic vapors and at temperatures from +250C to -30C. The variable temperature AFM studies can be performed at 5-10C/min heating/cooling rates and images can be collected at every temperature degree. Monitoring of structural changes, which accompany swelling, hydration, crystallization, melting, will be illustrated by studies of single brush macromolecules, liquid crystalline oligomers, polyethylene and polymer blends. A motion and conformational changes of brush macromolecules were observed during their aggregation and spreading in different vapors. The dynamic nanoscale changes were recorded during crystallization of low-density ethylene/octene copolymers. High-quality images at small and large scales, which can be routinely obtained in a fraction of minute, provide unseen efficiency of AFM analysis. |
Tuesday, March 6, 2018 4:30PM - 4:42PM |
H56.00007: Inelastic Neutron Scattering of Biaxially-Oriented Polyethylene Terephthalate (BoPET) Films Zachary Stroupe, Nicholas Strange, John Larese Polyethylene terephthalate (PET) has received considerable attention in recent years due to its ability to be generated from renewable materials that are biologically-based. Using the VISION spectrometer at the Spallation Neutron Source at Oak Ridge National Laboratory the inelastic neutron scattering (INS) spectrum has been measured for a thin sheet of biaxially oriented PET (BoPET) at low temperatures with the highest resolution attainable to date. Comparisons with earlier INS measurements of polyethylene films at the Rutherford Appleton Laboratory (J. Chem. Soc., Faraday Trans., 1996,92, 1941-1946) will be made. CASTEP (DFT) was used to optimize the structure of a model PET crystal and the corresponding vibrational spectrum was generated from coordinates and force constants. The INS spectrum in the current study of BoPET was generated using the classical Wilson GF matrix method. The phonon density of states was used to correct for dispersion in the vibrational spectrum. The calculated INS spectrum using this approach shows good agreement with the experimentally obtained results. |
Tuesday, March 6, 2018 4:42PM - 4:54PM |
H56.00008: nano-FTIR: Near-Field Spectroscopy of Polymers with sub-20nanometer Spatial Resolution Max Eisele, Adrian Cernescu Scattering-type scanning near-field optical microscopy (s-SNOM) has emerged as one of the key technologies to study the optical properties of physical, chemical and biological materials on the 10-nm length scale – far beyond the diffraction limit of light. Utilizing the strong confinement of the optical near-field at the apex of a sharp metal atomic-force microscope the tip, this technology is capable of detection the complex valued dielectric function of the materials directly below the tip. This way important information about the samples absorption and reflectivity can be extracted at the nanoscale. With the development of Fourier transform infrared spectroscopy on the nanoscale (nano-FTIR) and hyperspectral nanospectroscopy, we have successfully extended s-SNOM towards a complete spectroscopic analysis tool that is capable of analyzing complex polymer nanostructures, embedded structural phases in biominerals, organic semiconductors and two-dimensional materials. In this presentation we will introduce the basic principle of near-field microscopy, nano-FTIR spectroscopy and hyperspectral nanoscopy and address their impact and key applications in the field polymer characterization. |
Tuesday, March 6, 2018 4:54PM - 5:06PM |
H56.00009: Probing H- and J- aggregate spectral signatures via Stokes formalism for polarized light: applications to P3HT Steven Ulrich, Renato Sampaio, Huan Nguyen, Newton Barbosa, Paulo Araujo Spectroscopic measurements, particularly PL (and subsequently absorption measurements) have seen significant use as a means of probing H- and J- aggregate behavior in P3HT among other polymer systems. While excitonic transitions associated with these aggregate formations are readily obtained and visualized at low temperature (T<70K), thermal affects broaden their spectral signatures, making it difficult to accurately resolve signatures of one transition to another. Modeling, including Frank Condon fitting and numerical calculations have been able to deconvolute peaks from PL signatures, even from high temperature data (T>150K). However, these fitting techniques involve in depth fitting algorithms and don’t necessarily interact directly with acquired PL signatures, instead providing best fit approximations. Here, we show how the Stokes Formalism can be applied to acquire polarization dependent spectroscopic emission, and that the off axis linear polarization shows heightened resolution of aggregate emissions typically unresolvable at high temperature (T>150K). Subsequent analysis of this polarized emission is then used following proposed theory to obtain emission peak rations, coherence lengths, coherence numbers among other pertinent parameters. |
Tuesday, March 6, 2018 5:06PM - 5:18PM |
H56.00010: From Vesicles to Cylinders in MeBIP-containing Poly(acrylate)s Frederick Beyer, Alice Savage, Scott Walck, Robert Lambeth Supramolecular assembly of metallopolymers provides a wide parameter space in which morphology can be altered, without additional polymer synthesis, whether by changing the metal salt, adding free metal-ligand complex, or by addition of other compounds. Here, we have explored morphological behavior in a system based on a low molecular weight prepolymer of poly(n-butyl acrylate) containing 2,6-bis(1′-methylbenzimidazolyl)pyridine (MeBIP) -functionalized acrylate, synthesized using controlled radical techniques. MeBIP accounted for 2 to 10 percent of the prepolymer. Supramolecular assembly of the prepolymer by addition of Zn(ClO4)2 salt produced free-standing networked films. In most cases, an essentially amorphous and featureless material resulted. In one case, however, vesicles containing concentrated metal-ligand complex were observed. When small amounts of free MeBIP-salt complex were added to these materials supramolecular assemblies, a change in morphology from vesicles to cylinders was observed. Morphological behavior was monitored using small-angle X-ray scattering (SAXS), and probed extensively using high-angle annular dark field scanning TEM (HAADF STEM), energy dispersive X-ray spectroscopy (EDS), electron energy loss spectroscopy (EELS), and energy filtered TEM (EFTEM). |
Tuesday, March 6, 2018 5:18PM - 5:30PM |
H56.00011: The interplay of thermodynamics and kinetics: Imparting hierarchical control over film formation of self-stratified blends Samantha Rinehart, Mark Dadmun Spin casting is an attractive method to fabricate thin films found in electronic devices. Recent results investigate the impact of spin casting parameters on final film structure, and proved the impact of casting speed and molecular weight on film structure are due to the thermodynamic properties of surface energy and miscibility of the polymer blend, respectively. To determine the overarching thermodynamic property controlling final film structure, we monitor final film structures developed from the polymer blend of poly(3-hexylthiophene-2,5-diyl) and poly(methyl methacrylate) at controlled loading ratios, relative molecular weights, and casting speed. The structures of these thin films were characterized via neutron reflectivity, and the results show that at the fastest casting speed, enthalpy and surface energy of the blend dictate final film structure, and at the slowest casting speed, there is less control over the film orientation due to multiple thermodynamic properties simultaneously driving the stratification. These results broaden the current correlation between spin casting parameters and final polymer thin film architecture, providing routes to polymer thin film fabrication protocols that result in targeted structures. |
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