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Results for “Degree of polymerization”

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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Gaseous abundances and methane supersaturation in Titan's troposphere

Various properties of Titan's troposphere are inferred from an analysis of Voyager I infrared spectrometer (IRIS) data between 200 and 600/ cm. Two homogeneous spectral averages acquired at widely separated emission angles are chosen for the analysis. Both data sets are associated with northern low latitudes very close to that of the radio science ingress occultation point. Solutions require simultaneous nonlinear least-squares fits to the two IRIS data sets, coupled with iteration of the radio occultation refractivity data. Values and associated 1-sigma uncertainties of several parameters are inferred from our analysis. These include mole fractions for molecular hydrogen (approx. 0.0011), argon (small), and methane near the surface ( approx. 0.057). Solutions are also obtained for the hydrogen parafraction (close to equilibrium, with considerable uncertainty), air temperature near the surface ( approx. 93 K), surface surface temperature discontinuity (approx. 1 K), and maximum degree of methane supersaturation in the upper troposphere (approx. 1.5). Actual values for the above-mentioned parameters depend on the amount of ethane cloud near the tropopause. There is no evidence for methane clouds in the upper troposphere, nor is their presence compatible with large degrees of supersaturation. A wave number dependence for the stratospheric haze opacity is inferred similar to that found for a polymeric residue created in laboratory discharge experiments. This haze appears to be uniformly distributed with latitude between altitudes of 40 and 160 km, provided those nighttime data at southern high latitudes that are discounted.

Samuelson, Robert E.↗
DOE OSTI2026

FROMP-from-Monomer

This repository provides the 1D reaction-diffusion simulation engine for the multi-scale framework. It takes monomer-level kinetic and thermodynamic descriptors as inputs, approximated from quantum chemical calculations, to simulate and predict the macroscopic propagation behavior of Frontal Ring-Opening Metathesis Polymerization (FROMP). By solving a coupled 1D reaction-diffusion PDE system, this tool predicts front propagation speed, front temperature, and degree of conversion. The solver explicitly captures the three fundamental ROMP steps, initiator activation/inhibition, chain initiation, and propagation, while accounting for high-temperature cycloreversion as a competing pathway. The numerical implementation uses FEniCS to handle the coupled heat diffusion and reaction kinetics.

Chua, Lauren [Massachusetts Inst. of Technology (M↗
DOE OSTI2023

ATRP Enhances Structural Correlations In Polymerization–Induced Phase Separation**

Synthetic methods to control the structure of materials at sub–micron scales are typically based on the self–assembly of structural building blocks with precise size and morphology. On the other hand, many living systems can generate structure across a broad range of length scales in one step directly from macromolecules, using phase separation. Here, we introduce and control structure at the nano– and microscales through polymerization in the solid state, which has the unusual capability of both triggering and arresting phase separation. In particular, we show that atom transfer radical polymerization (ATRP) enables control of nucleation, growth, and stabilization of phase–separated poly–methylmethacrylate (PMMA) domains in a solid polystyrene (PS) matrix. ATRP yields durable nanostructures with low size dispersity and high degrees of structural correlations. Furthermore, we demonstrate that the length scale of these materials is controlled by the synthesis parameters.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Improving Miscibility of Polymer Donor and Polymer Acceptor by Reducing Chain Entanglement for Realizing 18.64 % Efficiency All Polymer Solar Cells

All-polymer solar cells have experienced rapid development in recent years by the emergence of polymerized small molecular acceptors (PSMAs). However, the strong chain entanglements of polymer donors (P D s) and polymer acceptors (P A s) decrease the miscibility of the resulting polymer mixtures, making it challenging to optimize the blend morphology. Herein, we designed three P A s, namely PBTPICm-BDD, PBTPICγ-BDD and PBTPICF-BDD, by smartly using a BDD unit as the polymerized unit to copolymerize with different Y-typed non-fullerene small molecular acceptors (NF-SMAs), thus achieving a certain degree of distortion and giving the polymer system enough internal space to reduce the entanglements of the polymer chains. Such effects increase the chances of the P D being interspersed into the acceptor material, which improve the solubility between the P D and P A . The PBTPICγ-BDD and PBTPICF-BDD displayed better miscibility with PBQx-TCl, leading to a well optimized morphology. As a result, high power conversion efficiencies (PCEs) of 17.50 % and 17.17 % were achieved for PBQx-TCl : PBTPICγ-BDD and PBQx-TCl : PBTPICF-BDD devices, respectively. In conclusion, with the addition of PYFT-o as the third component into PBQx-TCl : PBTPICγ-BDD blend to further extend the absorption spectral coverage and finely tune microstructures of the blend morphology, a remarkable PCE of 18.64 % was realized finally.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Deciphering the Distribution and Crystal-Chemical Environment of Arsenic, Lead, Silica, Phosphorus, Tin, and Zinc in a Porous Ferrihydrite Grain Using Transmission Electron Microscopy and Atom Probe Tomography

Here the interaction of contaminants and nutrients with soil constituents is controlled by processes in intergranular and intragranular pore spaces of organic matter or/and common secondary minerals such as ferrihydrite, ~Fe 3+ 10 O 14 (OH) 2 . This contribution shows that distribution and clustering of the contaminants As, P, Pb, Si, Sn, and Zn in a porous ferrihydrite grain is greatly affected by the heterogeneous size distribution and chemical composition of the pores as well as the ability of their polyhedra to polymerize with the same type of polyhedron. Transmission electron microscopy (TEM) and atom probe tomography (APT) studies are conducted on focused ion beam (FIB) sections extracted from a porous ferrihydrite grain from the smelter-impacted topsoil in Sudbury, Ontario, Canada. The ferrihydrite grain has pore spaces ranging in diameter from tens to hundreds of nanometers. TEM and scanning-TEM studies indicate that the surfaces of the pore walls are enriched in Si. APT data in conjunction with First Near Neighbor (1NN) analyses indicate different degrees of clustering of Pb, As, Sn, Zn, Si, and P within the sample and selected domains. Careful evaluations of 3D atomic plots and 1NN distances indicates the occurrence of polymerized arsenite-, silica-, Sn-, and Zn-polyhedra within pore spaces of the ferrihydrite. Deciphering adsorption, polymerization, and nucleation processes in porous Fe-(hydr)oxides and other soil constituents requires multianalytical approaches and, in this regard, we discuss the advantages and disadvantages of the combination of TEM and APT for characterizing complex environmental samples at the atomic to nanometer scale.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1992

Skylab D024 thermal control coatings and polymeric films experiment

The Skylab D024 Thermal Control Coatings and Polymeric Films Experiment was designed to determine the effects of the external Skylab space environment on the performance and properties of a wide variety of selected thermal control coatings and polymeric films. Three duplicate sets of thermal control coatings and polymeric films were exposed to the Skylab space environment for varying periods of time during the mission. The specimens were retrieved by the astronauts during extravehicular activities (EVA) and placed in hermetically sealed return containers, recovered, and returned to the Wright Laboratory/Materials Laboratory/WPAFB, Ohio for analysis and evaluation. Postflight analysis of the three sets of recovered thermal control coatings indicated that measured changes in specimen thermo-optical properties were due to a combination of excessive contamination and solar degradation of the contaminant layer. The degree of degradation experienced over-rode, obscured, and compromised the measurement of the degradation of the substrate coatings themselves. Results of the analysis of the effects of exposure on the polymeric films and the contamination observed are also presented. The D024 results were used in the design of the LDEF M0003-5 Thermal Control Materials Experiment. The results are presented here to call to the attention of the many other LDEF experimenters the wealth of directly related, low earth orbit, space environmental exposure data that is available from the ten or more separate experiments that were conducted during the Skylab mission. Results of these experiments offer data on the results of low altitude space exposure on materials recovered from space with exposure longer than typical STS experiments for comparison with the LDEF results.

Lehn, William L.↗
DOE OSTI2021

Pyroelectricity of Lead Sulfide (PbS) Quantum Dot Films Induced by Janus-Ligand Shells

Asymmetry is an essential property to control. To do that in nanocrystalline systems we have developed methods to produce Janus-ligand shells on otherwise symmetric PbS quantum dots (QDs). In this work, we demonstrate that control by constructing a system that exhibits pyroelectricity built from spherical PbS QDs. We observed a pyroelectric current in two different configurations. In one configuration, the QDs are self-assembled into close-packed arrays while in the second configuration, the QDs are dispersed into an electro-inactive polymer, polydimethylsiloxane. Both exhibit a pyroelectric response. In the first configuration we estimate a lower limit of the pyroelectric coefficient to be 1.97 × 10 -7 C/m 2 K, which is likely limited by the degree of QD alignment during film formation but is already on par with common pyroelectric systems. Compared with inorganic ceramic-like and polymeric pyroelectric materials, pyroelectric films self-assembled from polar QDs are easier to prepare, responsive to light with different energies based on QD exciton energy, and the polarization of each QD could be easily tuned by constructing different Janus-ligand shells.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1971

Effects of the thermal sterilization procedure on polymeric products

Properties of samples are tested, after thermal exposure, and values are compared with unexposed samples. Thermal stability or compatibility ratings of formulated or compounded organic polymers using trade names are made and degree of change in measured properties is assessed. Products are rated compatible, marginal, or not compatible.

Campbell, B. A.↗
NASA NTRS1989

PMR Resin Compositions For High Temperatures

Report describes experiments to identify polymer matrix resins suitable for making graphite-fiber laminates used at 700 degree F (371 degree C) in such applications as aircraft engines to achieve higher thrust-to-weight ratios. Two particular high-molecular-weight formulations of PMR (polymerization of monomer reactants) resins most promising. PMR compositions of higher FMW exhibit enhanced thermo-oxidative stability. Formation of high-quality laminates with these compositions requires use of curing pressures higher than those suitable for compositions of lower FMW.

Vannucci, Raymond D.↗
DOE OSTI2025

Thiol- and Disulfide-Functionalized Polycyclooctene: Metathesis Polymerization, Degradation, and Reformation

The enormous global production and use of polymers and plastics, combined with slower and less efficient disposal and recycling methods, have led to a worldwide growth in plastic waste. Here, we describe an approach that builds degradability into macromolecular polyolefins through the design of telechelic oligomers with reactive functional groups that enables control over polymer deconstruction and reconstruction. Our work exploits disulfide-containing polymers that have emerged as promising cyclable materials due to their dynamic reversibility (bond formation and cleavage) driven by redox chemistry under mild conditions. Specifically, we describe the synthesis of a telechelic α,ω-dithiopolycyclooctene (PCOE) by ring-opening metathesis polymerization using a dithioacetate chain transfer agent, followed by deprotection to convert the chain-end thioacetates to thiols. This process was studied towards control over the degree of oxidation to yield disulfide-containing PCOE, followed by an evaluation of reductive degradation and oxidative repolymerization. Overall, this approach facilitates the production of disulfide-containing unsaturated polyolefins and the integration of degradable and reformable moieties into soluble, processable, metathesis-derived polymers.

Lee, Kyoungwon↗
DOE OSTI2021

Biocompatible Electrostatic Layered Systems for Viral Elimination in the Nose/Throat

An anti-viral coating for the nose & throat is needed to quickly address the spread of COVID-19 infections and to aid future pandemics. Current nasal delivery systems are typically a 1-spray homogenous solution, which is convenient but may not be as efficient or durable as a multi-spray solution that contains a binding layer to anchor the anti-viral components. Many of the current nasal solutions being investigated to aid in pandemic response have solution-based mechanisms of action and are quickly cleared from the nose/mouth limiting their efficacy lifetime. A multi-spray approach utilizing strong intermolecular forces between polymeric materials and anti-viral agents to provide a robust biocompatible coating is expected to have increased physical and chemical properties to combat viral infection. This work evaluated which tailored biocompatible materials are needed to generate a layered system to combat viral infection. This layered system takes advantage of electrostatic interactions to bind anti-viral components, shown in Figure 1. Proof of concept success was demonstrated through cell toxicity studies and anti-viral assays on both the individual layer components and the complete layered system. Project work began with chemical modifications of Xantham Gum to hydrolyzing xanthan gum to give a negatively charged polymer with varying degrees of ionic character and investigate bonding efficiencies. However, this was abandoned in favor of comparing COTS available materials listed in Table 1 (Results section). Concentration and adhesion studies were performed on layers created using the listed polymeric materials and anti-viral agents. Finally, biocompatibility of materials, layers, and coating system were confirmed through cytotoxicity studies and the efficacy of the anti-viral properties tested with phi6 bacteriophage as a SARS-CoV2 surrogate.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Material Compatibility of Elastomers Used in the Salt Waste Processing Facility(SWPF)

Near the beginning of calendar year 2021, Salt Waste Processing Facility (SWPF) processed nearly a million gallons of initially diluted, and subsequently undiluted, supernatant. Higher than usual levels of Isopar L were detected in the Decontaminated Salt Solution (DSS). After shutting down the process and inspecting the DSS coalescers, personnel discovered the coalescers media appeared deformed and at least one had extruded out of the sealing surfaces. The gasket material was removed and sent to the Savannah River National Laboratory to possibly determine the cause of gasket degradation. A memorandum was issued documenting the results that could not rule out assembly error of the coalescer. For example, over torquing the gaskets beyond their recommended degree of compression, may have been a potential failure mode. SRNL recommended performing a quick compatibility test between the different process solutions used at SWPF and four different polymeric materials (the fifth one-Kalrez ® -arrived at the end of this test).

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS1994

In-situ polymerized PLOT columns III: divinylbenzene copolymers and dimethacrylate homopolymers

Studies of divinylbenzene copolymers and dimethacrylate homopolymers indicate that the polymer pore size controls the separation of water and ammonia on porous-layer-open-tubular (PLOT) columns. To a lesser degree, the polarity of the polymers also affects the separation of a water-ammonia gas mixture. Our results demonstrate that the pore size can be regulated by controlling the cross-linking density or the chain length between the cross-linking functional groups. An optimum pore size will provide the best separation of water and ammonia.

NASA Discipline Exobiology↗
DOE OSTI2020

Direct processing of PbZr 0.53 Ti 0.47 O 3 films on glass and polymeric substrates

This work reports on direct crystallization of PbZr 0.53 Ti 0.47 O 3 (PZT) thin films on glass and polymeric substrates, using pulsed thermal processing (PTP). Specifically, xenon flash lamps deliver pulses of high intensity, short duration, broadband light to the surface of a chemical solution deposited thin film, resulting in the crystallization of the film. Structural analysis by X-ray diffraction (XRD) and transmission electron microscopy show the existence of perovskite structure in nano-sized grains (≤5 nm). Local functional analysis by band excitation piezoelectric spectroscopy and electrostatic force microscopy confirm the presence of a ferroelectric phase and retention of voltage-written polarization for multiple days. Based on structural and functional analyses, strategies are discussed for optimization of pulse voltage and duration for the realization of crystalline ferroelectric thin films. For ~200 nm-thick PZT films on glass substrates, 500 μs-long pulses were required for crystallization, starting with 100 pulses at 350 V, 10 or 25 pulses at 400 V and in general lower number of pulses at higher voltages (resulting in higher radiant energy). Overall power densities of >6.4 kW/cm 2 were needed for appearance of peaks corresponding to the perovskite phase in the XRD. Films on glass processed at 350–400 V had a higher degree of 111-oriented perovskite grains. Higher applied radiant energy (through increased pulse voltage or count) resulted in more random and/or partially 001-oriented films. For ~1 μm-thick PZT films on polymeric substrates, 10 to 25 250 μs-long pulses at voltages ranging between 200 to 250 V, corresponding to power densities of ~2.8 kW/cm 2 , were optimal for maximized perovskite phase crystallization, while avoiding substrate damage.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Activated relaxation in supercooled monodisperse atomic and polymeric WCA fluids: Simulation and ECNLE theory

Here, we combine simulation and Elastically Collective Nonlinear Langevin Equation (ECNLE) theory to study the activated relaxation in monodisperse atomic and polymeric Weeks–Chandler–Andersen (WCA) liquids over a wide range of temperatures and densities in the supercooled regime under isochoric conditions. By employing novel crystal-avoiding simulations, metastable equilibrium dynamics is probed in the absence of complications associated with size polydispersity. Based on a highly accurate structural input from integral equation theory, ECNLE theory is found to describe well the simulated density and temperature dependences of the alpha relaxation time of atomic fluids using a single system-specific parameter, a c , that reflects the nonuniversal relative importance of local cage and collective elastic barriers. For polymer fluids, the explicit dynamical effect of local chain connectivity is modeled at the fundamental dynamic free energy trajectory level based on a different parameter, N c , that quantifies the degree of intramolecular correlation of bonded segment activated barrier hopping. For the flexible chain model studied, a physically intuitive value of N c ≈ 2 results in good agreement between simulation and theory. A direct comparison between atomic and polymeric systems reveals that chain connectivity can speed up activated segmental relaxation due to weakening of equilibrium packing correlations but can slow down relaxation due to local bonding constraints. The empirical thermodynamic scaling idea for the alpha time is found to work well at high densities or temperatures but fails when both density and temperature are low. The rich and subtle behaviors revealed from simulation for atomic and polymeric WCA fluids are all well captured by ECNLE theory.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Mixing ligands to enhance gas uptake in polyMOFs

Polymer-metal organic frameworks (polyMOFs) offer a pathway toward processable polymer–MOF hybrid materials; however, because polymeric ligands are incorporated throughout the MOF lattice, polyMOFs have an inherent shortcoming of reduced pore accessability and surface area compared to traditional MOFs. Herein, a strategy for altering the degree of polymer incorporation in polyMOFs by mixing a multivalent polymer ligand containing MOF-forming linkers with “free” linkers is investigated as a means to tune the properties of polyMOFs, resulting in polyMOFs with superior N 2 and CO 2 uptake. The mixed ligand approach is further extended to distinct MOF-forming polymer ligands to create multivariate (MTV)-polyMOFs, which provides a method for incorporating low-dispersity polymer ligands with complex architectures into polyMOF lattices without the addition of small molecule components.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Impact of polymer additives on crack mitigation of rod-coated fuel cell cathode catalyst layers

Cracks in catalyst layers (CLs) are a potential source of long-term failure in a fuel cell membrane electrode assembly (MEA). While modifications to the CL ink formulation can affect the degree of cracking, these changes may lead to lower initial performance than their cracked analogues due to the established link between formulation and performance. In this work, we explored the use of polymeric additives to mitigate CL cracks. Small quantities of poly (acrylic acid), poly (ethylene oxide), poly (methyl methacrylate), or poly (vinyl alcohol) - 5 wt% relative to ionomer mass - were added to the ink prior to its final mixing. Poly (vinyl alcohol) resulted in crack-free CLs, whereas the other polymers resulted in CLs with similar crack percentages as the control CL. Through a combination of transmission electron microscopy, X-ray computed tomography, and infrared spectroscopy, we ascribed the crack-mitigating mechanism of poly (vinyl alcohol) to its ability to hydrogen-bond with Nafion, the ion conducting polymer binder in the catalyst ink. Initial performance of this non-cracked electrode exhibited nearly identical electrochemical behavior to its cracked counterpart, demonstrating that PVA additives successfully reduce cracks while maintaining cell initial performance.

30 DIRECT ENERGY CONVERSION↗