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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Unifying Energetic Disorder from Charge Transport and Band Bending in Organic Semiconductors

Abstract Characterizing the density of states (DOS) width accurately is critical in understanding the charge‐transport properties of organic semiconducting materials as broader DOS distributions lead to an inferior transport. From a morphological standpoint, the relative densities of ordered and disordered regions are known to affect charge‐transport properties in films; however, a comparison between molecular structures showing quantifiable ordered and disordered regions at an atomic level and its impact on DOS widths and charge‐transport properties has yet to be made. In this work, for the first time, the DOS distribution widths of two model conjugated polymer systems are characterized using three different techniques. A quantitative correlation between energetic disorder from band‐bending measurements and charge transport is established, providing direct experimental evidence that charge‐carrier mobility in disordered materials is compromised due to the relaxation of carriers into the tail states of the DOS. Distinction and quantification of ordered and disordered regions of thin films at an atomic level is achieved using solid‐state NMR spectroscopy. An ability to compare solid‐state film morphologies of organic semiconducting polymers to energetic disorder, and in turn charge transport, can provide useful guidelines for applications of organic conjugated polymers in pertinent devices.

Karki, Akchheta↗
NASA NTRS2002

Characterization of the electromechanical properties of ionomeric polymer-metal composite (IPMC)

IPMC is an electroactive polymer (EAP) that has been the subject of research and development since 1992. Its required low activation voltage and the large bending strain led to its consideration for various potential applications. However, before the benefits of IPMC can be effectively exploited for practical use, the electromechanical behavior of this group of EAP materials must be properly understood and quantified.

EAP↗
DOE OSTI2013

Assessment and characterization of the total geometric uncertainty in Gamma Knife radiosurgery using polymer gels

Purpose: This work proposes and implements an experimental methodology, based on polymer gels, for assessing the total geometric uncertainty and characterizing its contributors in Gamma Knife (GK) radiosurgery. Methods: A treatment plan consisting of 26, 4-mm GK single shot dose distributions, covering an extended region of the Leksell stereotactic space, was prepared and delivered to a polymer gel filled polymethyl methacrylate (PMMA) head phantom (16 cm diameter) used to accurately reproduce every link in the GK treatment chain. The center of each shot served as a 'control point' in the assessment of the GK total geometric uncertainty, which depends on (a) the spatial dose delivery uncertainty of the PERFEXION GK unit used in this work, (b) the spatial distortions inherent in MR images commonly used for target delineation, and (c) the geometric uncertainty contributor associated with the image registration procedure performed by the Leksell GammaPlan (LGP) treatment planning system (TPS), in the case that registration is directly based on the apparent fiducial locations depicted in each MR image by the N-shaped rods on the Leksell localization box. The irradiated phantom was MR imaged at 1.5 T employing a T2-weighted pulse sequence. Four image series were acquired by alternating the frequency encoding axis and reversing the read gradient polarity, thus allowing the characterization of the MR-related spatial distortions. Results: MR spatial distortions stemming from main field (B{sub 0}) inhomogeneity as well as from susceptibility and chemical shift phenomena (also known as sequence dependent distortions) were found to be of the order of 0.5 mm, while those owing to gradient nonlinearities (also known as sequence independent distortions) were found to increase with distance from the MR scanner isocenter extending up to 0.47 mm at an Euclidean distance of 69.6 mm. Regarding the LGP image registration procedure, the corresponding average contribution to the total geometric uncertainty ranged from 0.34 to 0.80 mm. The average total geometric uncertainty, which also includes the GK spatial dose delivery uncertainty, was found equal to (0.88 {+-} 0.16), (0.88 {+-} 0.26), (1.02 {+-} 0.09), and (1.15 {+-} 0.24) mm for the MR image series acquired with the read gradient polarity (direction) set toward right, left, posterior, and anterior, respectively. Conclusions: The implemented methodology seems capable of assessing the total geometric uncertainty, as well as of characterizing its contributors, ascribed to the entire GK treatment delivery (i.e., from MR imaging to GK dose delivery) for an extended region of the Leksell stereotactic space. Results obtained indicate that the selection of both the frequency encoding axis and the read gradient polarity during MRI acquisition may affect the magnitude as well as the spatial components of the total geometric uncertainty.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1978

Characterization of wear debris generated in accelerated rolling-element fatigue tests

A ferrographic analysis was used to determine the types and quantities of wear debris generated during accelerated rolling contact fatigue tests. The five-ball rolling contact fatigue tester was used. Ball specimens were made of a corrosion resistant, high-temperature bearing steel. The lubricant was a superrefined naphthenic mineral oil. Conditions included a maximum Hertz stress of 5.52 10 to the 9th power Pa and a shaft speed of 10,000 rpm. Four types of wear debris were observed: (1) normal rubbing wear particles, (2) fatigue microspall particles, (3) spheres, and (4) friction polymer deposits. The characterization of wear debris as a function of time was of limited use in predicting fatigue failures in these accelerated tests.

Jones, W. R., Jr.↗
NASA NTRS2004

High Temperature Polymers for use in Fuel Cells

NASA Glenn Research Center (GRC) is currently working on polymers for fuel cell and lithium battery applications. The desire for more efficient, higher power density, and a lower environmental impact power sources has led to interest in proton exchanges membrane fuels cells (PEMFC) and lithium batteries. A PEMFC has many advantages as a power source. The fuel cell uses oxygen and hydrogen as reactants. The resulting products are electricity, heat, and water. The PEMFC consists of electrodes with a catalyst, and an electrolyte. The electrolyte is an ion-conducting polymer that transports protons from the anode to the cathode. Typically, a PEMFC is operated at a temperature of about 80 C. There is intense interest in developing a fuel cell membrane that can operate at higher temperatures in the range of 80 C- 120 C. Operating the he1 cell at higher temperatures increases the kinetics of the fuel cell reaction as well as decreasing the susceptibility of the catalyst to be poisoned by impurities. Currently, Nafion made by Dupont is the most widely used polymer membrane in PEMFC. Nafion does not function well above 80 C due to a significant decrease in the conductivity of the membrane from a loss of hydration. In addition to the loss of conductivity at high temperatures, the long term stability and relatively high cost of Nafion have stimulated many researches to find a substitute for Nafion. Lithium ion batteries are popular for use in portable electronic devices, such as laptop computers and mobile phones. The high power density of lithium batteries makes them ideal for the high power demand of today s advanced electronics. NASA is developing a solid polymer electrolyte that can be used for lithium batteries. Solid polymer electrolytes have many advantages over the current gel or liquid based systems that are used currently. Among these advantages are the potential for increased power density and design flexibility. Automobiles, computers, and cell phones require highly efficient power density for lowering emissions and meeting increasing consumer demands. Many of the solutions can be provided by proton exchange membrane fuel cells and lithium batteries. NASA Glenn Research Center has recognized this need, and is presently engaged in a solution. The goals for the summer include mastering synthesis techniques, understanding the reactions occurring during the synthesis, and characterizing the resulting polymer membranes using NMR, DSC, and TGA for the PEMFC and lithium batteries.

Peplowski, Katherine M.↗
DOE OSTI2019

Chapter 5.01 - Organic Electronic Devices With Water-Dispersible Conducting Polymers

This chapter details the history, chemistry, characterization, and application of water-dispersible conducting polymers. These materials can be produced through versatile synthetic routes and possess unique doping chemistries. The nature of their conductivity has been investigated through characterization of optical, electrochemical, and structural properties. Applications in thin-film transistors, light-emitting diodes, solar cells, and electrochromic devices are described.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1999

Strain Rate Dependent Deformation and Strength Modeling of a Polymer Matrix Composite Utilizing a Micromechanics Approach

Potential gas turbine applications will expose polymer matrix composites to very high strain rate loading conditions, requiring an ability to understand and predict the material behavior under extreme conditions. Specifically, analytical methods designed for these applications must have the capability of properly capturing the strain rate sensitivities and nonlinearities that are present in the material response. The Ramaswamy-Stouffer constitutive equations, originally developed to analyze the viscoplastic deformation of metals, have been modified to simulate the nonlinear deformation response of ductile, crystalline polymers. The constitutive model is characterized and correlated for two representative ductile polymers. Fiberite 977-2 and PEEK, and the computed results correlate well with experimental values. The polymer constitutive equations are implemented in a mechanics of materials based composite micromechanics model to predict the nonlinear, rate dependent deformation response of a composite ply. Uniform stress and uniform strain assumptions are applied to compute the effective stresses of a composite unit cell from the applied strains. The micromechanics equations are successfully verified for two polymer matrix composites. IM7/977-2 and AS4/PEEK. The ultimate strength of a composite ply is predicted with the Hashin failure criteria that were implemented in the composite micromechanics model. The failure stresses of the two composite material systems are accurately predicted for a variety of fiber orientations and strain rates. The composite deformation model is implemented in LS-DYNA, a commercially available transient dynamic explicit finite element code. The matrix constitutive equations are converted into an incremental form, and the model is implemented into LS-DYNA through the use of a user defined material subroutine. The deformation response of a bulk polymer and a polymer matrix composite are predicted by finite element analyses. The results compare reasonably well to experimental values, with some discrepancies. The discrepancies are at least partially caused by the method used to integrate the rate equations in the polymer constitutive model.

Goldberg, Robert K.↗
DOE OSTI2017

Tuning Block Polymer Structure, Properties, and Processability for the Design of Efficient Nanostructured Materials Systems

Block polymers (BPs) are ideal building blocks for nanoporous membranes, microelectronics templates, energy storage devices, and other technologies. For these systems, precise control over morphology, properties, and processability are essential to optimize performance. The Epps group has used a multidisciplinary approach to control BP nanostructure ordering and orientations, order-disorder and glass transition temperatures, and mechanical and transport properties through the informed manipulation of BP effective segregation strengths and interfacial energetics. For example, alterations in macromolecular interactions between BP chains were achieved through the introduction of composition gradients between copolymer blocks or by adding dopants. In thin films, high-throughput approaches were designed to modify and characterize substrate-polymer interactions, and solvent annealing techniques were developed to facilitate nanoscale alignment and ordering. Finally, by manipulating BP interfacial energetics to gain exquisite tunability of nanostructures and materials' properties, the group is accelerating the development of next-generation BPs that will be harnessed to fabricate inexpensive, efficient, and high-performance devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Molecular Characterization of High Molecular Weight Polyesters by Matrix-Assisted Laser Desorption/Ionization High-Resolution Time-of-Flight Mass Spectrometry Combined with On-plate Alkaline Degradation and Mass Defect Analysis

Matrix-assisted laser desorption ionization high-resolution time-of-flight mass spectrometry (MALDI HR TOF MS) is a powerful tool for the molecular characterization of industrial polymers. However, accurate mass determination and resolution of isobaric ions are possible for oligomer samples only typically below m/z 3000. To cut long polymer chains into oligomers suitable for high-resolution mass spectrometry, we propose a simple “on-plate” alkaline degradation of polyesters as a sample pretreatment technique prior to the MALDI TOF MS measurement. This pretreatment can be performed on a MALDI target using a small amount of sample (μg or less) and 1 μL of alkaline reagent by simple pipetting. Informative mass spectra in the oligomeric mass range are successfully recorded but complicated by the variation of end-groups and the copolymeric composition of the degradation products. Data processing is assisted by a series of advanced Kendrick mass defect (KMD) analyses recently proposed by the authors to plot visually understandable two-dimensional maps. On-plate degradation pretreatment, high-resolution MALDI TOF MS measurements, and advanced KMD analyses are innovatively combined for the compositional characterization of bacterial poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) and industrial poly(ethylene terephthalate) samples. .

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

Structural variability in Cu(I) and Ag(I) coordination polymers with a flexible dithione ligand: Synthesis, crystal structure, microbiological and theoretical studies

Two new compounds namely [Cu(SCN)(µ-L)]{sub n} (1) and ([Ag (µ{sub 2}-L)](ClO{sub 4})){sub n} (2) have been synthesized at room temperature by one-pot reactions between the 1,1-(1,4-butanediyl)bis(1,3-dihydro-3-methyl-1H-imidazole- 2-thione) (L) and appropriate copper(I) and silver(I) salts. These polymers have been characterized by single crystal X-ray diffraction, XRPD, TGA, elemental analysis, infrared spectroscopy, antibacterial activity and scanning probe microscopy studies. In the crystal structure of 1, copper atoms have a distorted trigonal planar geometry with a CuS{sub 2}N coordination environment. Each of the ligands in the structure of 1 acting as a bidentate S-bridging ligand to form a 1D chain structure. Additionally, the adjacent 1D chains are interconnected by the intermolecular C-H…S interactions to create a 2D network structure. In contrast to 1, in the cationic 3D structure of 2 each of the silver atoms exhibits an AgS{sub 4} tetrahedral geometry with 4-membered Ag{sub 2}S{sub 2} rings. In the structure of 2, the flexible ligand adopts two different conformations; gauche-anti-gauche and anti-anti-anti. The antibacterial studies of these polymers showed that polymer 2 is more potent antibacterial agent than 1. Scanning probe microscopy (SPM) study of the treated bacteria was carried out to investigate the structural changes cause by the interactions between the polymers and target bacteria. Theoretical study of polymer 1 investigated by the DFT calculations indicates that observed transitions at 266 nm and 302 nm in the UV–vis spectrum could be attributed to the π→π* and MLCT transitions, respectively. - Graphical abstract: Two new Cu(I) and Ag(I) coordination polymers have been have been synthesized by one-pot reactions. Copper complex has a 2D non-covalent structure, but silver compound is a 3D coordination compound. These compounds have effective antibacterial activity. - Highlights: • Cu(I) and Ag(I) based coordination polymers have different network structures. • Ag(I) polymer has more antibacterial activity than Cu(I) polymer. • DFT calculations of Cu(I) polymer has been investigated. • Cu(I) and Ag(I) polymers can destroy the structure of chromosomal and plasmid DNA.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Effects of Intercalating Molecules on the Polymer Properties of DNA

Atomic force microscopy (AFM) enables determination of physical properties from single DNA molecules. Insertion of aromatic molecules into the structure of DNA results in morphological changes. However, the accompanying changes to elastic properties due to this insertion are not fully understood. AFM was used to examine the morphological effects of intercalator binding and report changes in the elastic properties of intrinsically straight DNA molecules. The persistence length and polymer extension were characterized in the presence of three intercalating molecules: ethidium bromide and the less well studied chloroquine and acridine. It was found that all three intercalators significantly increased the bending persistence length. In addition, an analysis of the normal bending modes of the static molecules corroborated these results. Furthermore, this approach of measuring binding effects of intercalators on DNA physical properties using a model system of intrinsically straight DNA is applicable to other DNA binding ligands and other modes of DNA interaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Trace Compound Analysis in TATB by Liquid Chromatography coupled with Spectroscopic and Spectrometric Detection

Accurate quantitation of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) is important because of its strategic use as an energetic material. A purity determination is also needed for the proper assessment of performance. A fast and sensitive method has been developed to measure the purity of TATB in polymer-bonded materials. The target material is extracted with DMSO, and the extract is separated on a reversed-phase chromatography column. The column effluent is monitored by diode array detection (DAD) at 354 nm. The characteristic UV-Vis response and retention time identify the individual components when compared to pure compound standards. The chemical structures of compounds with no pure standards available have been determined by high-resolution mass spectrometry (MS) and MS/MS. The major component, TATB, along with 1-chloro-3,5-dinitro-2,4,6-triaminobenzene (T4A) and mono-benzofuroxan (FX1) were quantitated directly from pure compound standards. Several trace concentration components, mono-benzofurazan (F1), 1-bromo-3,5-dinitro-2,4,6-triaminobenzene (Br-T4A), 2,4,6-triamino-1-nitroso-3,5-dinitrobenzene (MN-TATB), 2,4,6-triamino-1-hydroxyl-3,5-dinitrobenzene (HO-TATB), and 2,4,6-triamino-1-nitrile-3,5-dinitrobenzene (Nitrile-TATB) were also detected and structures verified via MS/MS. Approximate concentrations were determined using calibrations from standards of similar structures. Additional trace components were also detected by MS. Contained herein are the results of analyses of TATB-based materials characterized for polymer-bonded formulations compared to different preparations of TATB. The accuracy, details, and process of developing this method are reported here.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Solution-processable and functionalizable ultra-high molecular weight polymers via topochemical synthesis

Abstract Topochemical polymerization reactions hold the promise of producing ultra-high molecular weight crystalline polymers. However, the totality of topochemical polymerization reactions has failed to produce ultra-high molecular weight polymers that are both soluble and display variable functionality, which are restrained by the crystal-packing and reactivity requirements on their respective monomers in the solid state. Herein, we demonstrate the topochemical polymerization reaction of a family of para -azaquinodimethane compounds that undergo facile visible light and thermally initiated polymerization in the solid state, allowing for the first determination of a topochemical polymer crystal structure resolved via the cryoelectron microscopy technique of microcrystal electron diffraction. The topochemical polymerization reaction also displays excellent functional group tolerance, accommodating both solubilizing side chains and reactive groups that allow for post-polymerization functionalization. The thus-produced soluble ultra-high molecular weight polymers display superior capacitive energy storage properties. This study overcomes several synthetic and characterization challenges amongst topochemical polymerization reactions, representing a critical step toward their broader application.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

A Bayesian Approach to Predict Solubility Parameters

Abstract Solubility is a ubiquitous phenomenon in many aspects of material science. While solubility can be determined by considering the cohesive forces in a liquid via the Hansen solubility parameters (HSP), quantitative structure–property relationship models are often used for prediction, notably due to their low computational cost. Here, gpHSP, an interpretable and versatile probabilistic approach to determining HSP, is reported. Our model is based on Gaussian processes, a Bayesian machine learning approach that provides uncertainty bounds to prediction. gpHSP achieves its flexibility by leveraging a variety of input data, such as SMILES strings, COSMOtherm simulations, and quantum chemistry calculations. gpHSP is built on experimentally determined HSP, including a general solvents set aggregated from the literature, and a polymer set experimentally characterized by this group of authors. In all sets, a high degree of agreement is obtained, surpassing well‐established machine learning methods. The general applicability of gpHSP to miscibility of organic semiconductors, drug compounds, and in general solvents is demonstrated, which can be further extended to other domains. gpHSP is a fast and accurate toolbox, which could be applied to molecular design for solution processing technologies.

Sanchez‐Lengeling, Benjamin↗
DOE OSTI2021

Strain-Induced Nanocavitation in Block Copolymer Thin Films for High Performance Filtration Membranes

A new pore formation process was investigated for the manufacture of composite ultrafiltration membranes. Phase-separated block copolymer (BCP) thin films supported on a compliant macroporous poly(ether sulfone) (PES) support craze under tensile strain, leaving behind pores of predictable size based on the self-assembled nanoscopic domains. The high aspect ratio pores formed in this process were used to create membranes that were highly permeable (959 L/(m 2 h bar) with near complete rejection of 40 nm diameter gold nanoparticles (AuNP). By use of BCP’s inherent ability to cavitate under strain, tedious block removal steps are avoided. Membranes can thus be prepared in a simple, roll-to-roll ready, one-step process. In this initial study, BCP craze formation and filtration performance were characterized for various polymer types, molecular weights, and thicknesses. Furthermore, all these factors influenced the BCP’s thin film morphology, mechanical performance, deformation mechanism, and ultimately filtration performance. This work demonstrates a possible new path toward achieving scalable, BCP-based ultrafiltration membranes.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Combined hydrophobicity and mechanical durability through surface nanoengineering

This paper reports combined hydrophobicity and mechanical durability through the nanoscale engineering of surfaces in the form of nanorod-polymer composites. Specifically, the hydrophobicity derives from nanoscale features of mechanically hard ZnO nanorods and the mechanical durability derives from the composite structure of a hard ZnO nanorod core and soft polymer shell. Experimental characterization correlates the morphology of the nanoengineered surfaces with the combined hydrophobicity and mechanical durability, and reveals the responsible mechanisms. Such surfaces may find use in applications, such as boat hulls, that benefit from hydrophobicity and require mechanical durability.

77 NANOSCIENCE AND NANOTECHNOLOGY↗