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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Single Turnover at Molecular Polymerization Catalysts Reveals Spatiotemporally Resolved Reactions

Abstract Multiple active individual molecular ruthenium catalysts have been pinpointed within growing polynorbornene, thereby revealing information on the reaction dynamics and location that is unavailable through traditional ensemble experiments. This is the first single‐turnover imaging of a molecular catalyst by fluorescence microscopy and allows detection of individual monomer reactions at an industrially important molecular ruthenium ring‐opening metathesis polymerization (ROMP) catalyst under synthetically relevant conditions (e.g. unmodified industrial catalyst, ambient pressure, condensed phase, ca. 0.03 m monomer). These results further establish the key fundamentals of this imaging technique for characterizing the reactivity and location of active molecular catalysts even when they are the minor components.

Easter, Quinn T.↗
DOE OSTI2017

Formation of Polymeric Nanocubes by Self‐Assembly and Crystallization of Dithiolane‐Containing Triblock Copolymers

Abstract Template‐free fabrication of non‐spherical polymeric nanoparticles is desirable for various applications, but has had limited success owing to thermodynamic favorability of sphere formation. Herein we present a simple way to prepare cubic nanoparticles of block copolymers by self‐assembly from aqueous solutions at room temperature. Nanocubes with edges of 40–200 nm are formed spontaneously on different surfaces upon water evaporation from micellar solutions of triblock copolymers containing a central poly(ethylene oxide) block and terminal trimethylene carbonate/dithiolane blocks. These polymers self‐assemble into 28±5 nm micelles in water. Upon drying, micelle aggregation and a kinetically controlled crystallization of central blocks evidently induce solid cubic particle formation. An approach for preserving the structures of these cubes in water by thiol‐ or photo‐induced crosslinking was developed. The ability to solubilize a model hydrophobic drug, curcumin, was also explored.

Margulis, Katherine↗
DOE OSTI2018

ipso ‐Arylative Ring‐Opening Polymerization as a Route to Electron‐Deficient Conjugated Polymers

Abstract ipso ‐Arylative ring‐opening polymerization of 2‐bromo‐8‐aryl‐8 H ‐indeno[2,1‐b]thiophen‐8‐ol monomers proceeds to M n up to 9 kg mol −1 with conversion of the monomer diarylcarbinol groups to pendent conjugated aroylphenyl side chains (2‐benzoylphenyl or 2‐(4‐hexylbenzoyl)phenyl), which influence the optical and electronic properties of the resulting polythiophenes. Poly(3‐(2‐(4‐hexylbenzoyl)phenyl)thiophene) was found to have lower frontier orbital energy levels (HOMO/LUMO=−5.9/−4.0 eV) than poly(3‐hexylthiophene) owing to the electron‐withdrawing ability of the aryl ketone side chains. The electron mobility (ca. 2×10 −3 cm 2 V −1 s −1 ) for poly(3‐(2‐(4‐hexylbenzoyl)phenyl)thiophene) was found to be significantly higher than the hole mobility (ca. 8×10 −6 cm 2 V −1 s −1 ), which suggests such polymers are candidates for n‐type organic semiconductors. Density functional theory calculations suggest that backbone distortion resulting from side‐chain steric interactions could be a key factor influencing charge mobilities.

Shih, Feng‐Yang↗
DOE OSTI2020

High-Pressure Synthesis of Metal–Inorganic Frameworks Hf 4 N 20 •N 2 , WN 8 •N 2 , and Os 5 N 28 •3N 2 with Polymeric Nitrogen Linkers

Polynitrides are intrinsically thermodynamically unstable at ambient conditions and require peculiar synthetic approaches. Now, a one-step synthesis of metal–inorganic frameworks Hf 4 N 20 •N 2 , WN 8 •N 2 , and Os 5 N 28 •3N 2 via direct reactions between elements in a diamond anvil cell at pressures exceeding 100 GPa is reported. The porous frameworks (Hf 4 N 20 , WN 8 , and Os 5 N 28 ) are built from transition-metal atoms linked either by polymeric polydiazenediyl (polyacetylene-like) nitrogen chains or through dinitrogen units. Triply bound dinitrogen molecules occupy channels of these frameworks. Owing to conjugated polydiazenediyl chains, these compounds exhibit metallic properties. The high-pressure reaction between Hf and N 2 also leads to a non-centrosymmetric polynitride Hf 2 N 11 that features double-helix catena-poly[tetraz-1-ene-1,4-diyl] nitrogen chains [–N–N–N=N–] ∞ .

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

Does Selectivity of Molecular Catalysts Change with Time? Polymerization Imaged by Single‐Molecule Spectroscopy

Abstract The chemoselectivity of molecular catalysts underpins much of modern synthetic organic chemistry. However, little is known about the selectivity of individual catalysts because this single‐catalyst‐level behavior is hidden by the bulk catalytic behavior. Here, for the first time, the selectivity of individual molecular catalysts for two different reactions is imaged in real time at the single‐catalyst level. This imaging is achieved through fluorescence microscopy paired with spectral probes that produce a snapshot of the instantaneous chemoselectivity of a single catalyst for either a single‐chain‐elongation or a single‐chain‐termination event during ruthenium‐catalyzed polymerization. Superresolution imaging of multiple selectivity events, each at a different single‐molecular ruthenium catalyst, indicates that catalyst selectivity may be unexpectedly spatially and time‐variable.

Garcia, IV, Antonio↗
DOE OSTI2022

A Heterogeneous Palladium Catalyst for the Polymerization of Olefins Prepared by Halide Abstraction Using Surface R 3 Si + Species

Abstract The silylium‐like surface species [ i Pr 3 Si][(R F O) 3 Al−OSi≡)] activates (N^N)Pd(CH 3 )Cl (N^N=Ar−N=CMeMeC=N−Ar, Ar=2,6‐bis(diphenylmethyl)‐4‐methylbenzene) by chloride ion abstraction to form [(N^N)Pd−CH 3 ][(R F O) 3 Al−OSi≡)] ( 1 ). A combination of FTIR, solid‐state NMR spectroscopy, and reactions with CO or vinyl chloride establish that 1 shows similar reactivity patterns as (N^N)Pd(CH 3 )Cl activated with Na[B(Ar F ) 4 ]. Multinuclear 13 C{ 27 Al} RESPDOR and 1 H{ 19 F} S‐REDOR experiments are consistent with a weakly coordinated ion‐pair between (N^N)Pd−CH 3 + and [(R F O) 3 Al−OSi≡)]. 1 catalyzes the polymerization of ethylene with similar activities as [(N^N)Pd−CH 3 ] + in solution and incorporates up to 0.4 % methyl acrylate in copolymerization reactions. 1 produces polymers with significantly higher molecular weight than the solution catalyst, and generates the highest molecular weight polymers currently reported in copolymerization reactions of ethylene and methylacrylate.

Gao, Jiaxin↗
DOE OSTI2023

Anion-tethered Single Lithium-ion Conducting Polyelectrolytes through UV-induced Free Radical Polymerization for Improved Morphological Stability of Lithium Metal Anodes

Single Li + ion conducting polyelectrolytes (SICs), which feature covalently tethered counter-anions along their backbone, have the potential to mitigate dendrite formation by reducing concentration polarization and preventing salt depletion. However, due to their low ionic conductivity and complicated synthetic procedure, the successful validation of these claimed advantages in lithium metal (Li 0 ) anode batteries remains limited. In this study, we fabricated a SIC electrolyte using a single-step UV polymerization approach. The resulting electrolyte exhibited a high Li + transference number (t + ) of 0.85 and demonstrated good Li + conductivity (6.3×10 -5 S/cm at room temperature), which is comparable to that of a benchmark dual ion conductor (DIC, 9.1×10 -5 S/cm). Benefitting from the high transference number of SIC, it displayed a three-fold higher critical current density (2.4 mA/cm 2 ) compared to DIC (0.8 mA/cm 2 ) by successfully suppressing concentration polarization-induced short-circuiting. Additionally, the t + significantly influenced the deposition behavior of Li0, with SIC yielding a uniform, compact, and mosaic-like morphology, while the low t + DIC resulted in a porous morphology with Li 0 whiskers. Using the SIC electrolyte, Li 0 ||LiFePO 4 cells exhibited stable operation for 4500 cycles with 70.5 % capacity retention at 22 °C.

25 ENERGY STORAGE↗
DOE OSTI2017

Formation of Polymeric Nanocubes by Self-Assembly and Crystallization of Dithiolane-Containing Triblock Copolymers

Template–free fabrication of non–spherical polymeric nanoparticles is desirable for various applications, but has had limited success owing to thermodynamic favorability of sphere formation. Herein we present a simple way to prepare cubic nanoparticles of block copolymers by self–assembly from aqueous solutions at room temperature. Nanocubes with edges of 40–200 nm are formed spontaneously on different surfaces upon water evaporation from micellar solutions of triblock copolymers containing a central poly(ethylene oxide) block and terminal trimethylene carbonate/dithiolane blocks. These polymers self–assemble into 28±5 nm micelles in water. Upon drying, micelle aggregation and a kinetically controlled crystallization of central blocks evidently induce solid cubic particle formation. An approach for preserving the structures of these cubes in water by thiol– or photo–induced crosslinking was developed. In conclusion, the ability to solubilize a model hydrophobic drug, curcumin, was also explored.

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

High-Pressure Synthesis of Metal–Inorganic Frameworks Hf 4 N 20 ·N 2 , WN 8 ·N 2 , and Os 5 N 28 ·3 N 2 with Polymeric Nitrogen Linkers

Polynitrides are intrinsically thermodynamically unstable at ambient conditions and require peculiar synthetic approaches. Now, a one-step synthesis of metal–inorganic frameworks Hf 4 N 20 ·N 2 , WN 8 ·N 2 , and Os 5 N 28 ·3 N 2 via direct reactions between elements in a diamond anvil cell at pressures exceeding 100 GPa is reported. The porous frameworks (Hf 4 N 20 , WN 8 , and Os 5 N 28 ) are built from transition-metal atoms linked either by polymeric polydiazenediyl (polyacetylene-like) nitrogen chains or through dinitrogen units. Triply bound dinitrogen molecules occupy channels of these frameworks. Owing to conjugated polydiazenediyl chains, these compounds exhibit metallic properties. The high-pressure reaction between Hf and N 2 also leads to a non-centrosymmetric polynitride Hf 2 N 11 that features double-helix catena-poly[tetraz-1-ene-1,4-diyl] nitrogen chains [–N–N–N=N–] ∞ .

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

Anion-tethered Single Lithium-ion Conducting Polyelectrolytes through UV-induced Free Radical Polymerization for Improved Morphological Stability of Lithium Metal Anodes

Single Li + ion conducting polyelectrolytes (SICs), which feature covalently tethered counter-anions along their backbone, have the potential to mitigate dendrite formation by reducing concentration polarization and preventing salt depletion. However, due to their low ionic conductivity and complicated synthetic procedure, the successful validation of these claimed advantages in lithium metal (Li 0 ) anode batteries remains limited. In this study, we fabricated a SIC electrolyte using a single-step UV polymerization approach. The resulting electrolyte exhibited a high Li + transference number (t + ) of 0.85 and demonstrated good Li + conductivity (6.3×10 -5 S/cm at room temperature), which is comparable to that of a benchmark dual ion conductor (DIC, 9.1×10 -5 S/cm). Benefitting from the high transference number of SIC, it displayed a three-fold higher critical current density (2.4 mA/cm 2 ) compared to DIC (0.8 mA/cm 2 ) by successfully suppressing concentration polarization-induced short-circuiting. Additionally, the t + significantly influenced the deposition behavior of Li 0 , with SIC yielding a uniform, compact, and mosaic-like morphology, while the low t + DIC resulted in a porous morphology with Li 0 whiskers. In conclusion, using the SIC electrolyte, Li 0 ||LiFePO 4 cells exhibited stable operation for 4500 cycles with 70.5 % capacity retention at 22 °C.

25 ENERGY STORAGE↗
DOE OSTI2026

Supramolecular Arene‐Perfluoroarene Assembly Enhances Photoiniferter Polymerization Kinetics

Ultra-high-molecular-weight (UHMW, >106 Da) polymers have unique thermomechanical properties due to their large number of physical entanglements. Producing UHMW styrenic polymers is challenging because of their prohibitively slow homopolymerization kinetics. In this report, we show that alternating photoiniferter copolymerization between methoxy-functionalized styrenic monomers and pentafluorostyrene can circumvent this limitation under conditions where arene–perfluoroarene (AP) interactions contribute to favorable monomer association and accelerate copolymerization. Increasing methoxy substitution on the styrene arene ring leads to pronounced rate enhancements that correlate with electronic complementarity between the styrenic comonomers. Density functional theory calculations reveal increasingly favorable AP interaction energies across the series, consistent with monomer association contributing to faster propagation. The result is up to 2000% enhancement in propagation rate in copolymerizations compared to styrene homopolymerization. Despite these rate enhancements, the resulting materials retain broadly similar glass-transition temperatures and network-like thermomechanical behavior, with only modest softening across the series. Here, we then leverage the approach to produce UHMW trialkoxystyrene copolymers bearing sterically encumbered pendants, which are ultrasoft (Young's modulus of 8 kPa) and highly extensible (560%). These results establish that designed supramolecular association between styrenics is a powerful tool for controlling reactivity in radical polymerization and generating otherwise difficult-to-obtain materials.

Marquez, Joshua D. [University of Florida, Gainesv↗
DOE OSTI2020

Hydrazone-Linked Heptazine Polymeric Carbon Nitrides for Synergistic Visible-Light-Driven Catalysis

Heptazine-based conjugated polymeric carbon nitrides (PCNs) are promising metal-free photocatalysts, yet their synthesis is challenging due to the electron-deficiency and insolubility of heptazine units. Indeed, heptazine-containing polymers have only been prepared through nucleophilic substitution with amines by using toxic cyameluric chloride as the starting material. Herein, we report the novel and environmentally friendly method for preparing heptazine-based mesoporous PCNs with hydrazone links formed through a simple Schiff base condensation of melem-NH 2 and aldehydes. Unlike cyameluric chloride, melem-NH 2 is non-toxic, stable, and can be readily obtained from melem and hydrazine in solution. We demonstrate that the hydrazone linkages and the heptazine units synergistically enhance the photocatalytic activity of PCNs in visible-light-driven aerobic oxidation of benzyl alcohol to benzaldehyde. In particular, the polymer constructed from melem-NH2 and p-phthalaldehyde shows 17 times more activity than graphitic carbon nitride (g-C 3 N 4 ).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Improved ambient-stable perovskite solar cells enabled by a hybrid polymeric electron-transporting layer

In this study, an efficient inverted perovskite solar cell with decent ambient stability is successfully demonstrated by employing an n-type polymer, poly{[ N,N’ -bis(2-octyldodecyl)- 1,4,5,8-naphthalene diimide-2,6-diyl]- alt -5,5’-(2,2’-bithiophene)} (N2200), as the electron-transporting layer (ETL). The device performance can be further enhanced from a power conversion efficiency (PCE) of 15 to 16.8% by tailoring the electronic properties of N2200 with a polymeric additive, poly[9,9-bis(6’- ( N,N’ -diethylamino)propyl)-fluorene- alt -9,9-bis(3-ethyl(oxetane- 3-ethyloxy)-hexyl) fluorene] (PFN-Ox). More importantly, the device derived from this hybrid ETL can maintain good ambient stability inherent from the pristine N2200 ETL, for which 60–70% of initial PCE can be retained after being stored in air with 10–20% humidity for 45 days.

14 SOLAR ENERGY↗
DOE OSTI2020

Combining Chemistry, Material Science, Inspiration from nature, and Serendipity to Develop Stimuli-responsive Polymeric Materials

Neither of us can remember people talking about stimuli-responsive polymers when we were students. Even though this was still in the last century, it was almost 70 years after Staudinger's seminal paper "uber Polymerisation"![1] By the time we entered graduate school in the early 1990 s, the first papers on polymer light emitting diodes appeared, while research on electrically conducting, nonlinear optical, and other "functional" polymers was already in full swing. Looking back, there were some stimuli-responsive materials that were around at the time, but it took the better part of the last 30 years until the field had developed into what we think is one of the most vibrant areas of polymer science. Before the potential usefulness of this class of materials was recognized, researchers were focused on developing polymeric materials that would not respond to external influences, and in fact maintain (in particular) their mechanical properties in a wide range of environments. This has led to the development of many environmentally robust polymers, which have come to impact basically every aspect of our daily life. Ironically, this long-sought stability now comes back to haunt us in the form of plastic pollution, but this is another story. The concept of materials that adapt their properties in response to changing environmental conditions might appear like a complete reversal with respect to the original goals of creating stable materials. However, eventually a) it was recognized that materials that respond to a specific stimulus in a predictable and useful manner would significantly broaden the potential usefulness of polymers, and b) the field of polymer science had developed to the point where the rational design, preparation, and characterization of such materials became possible. The expression 'stimuli-responsive polymer' had been first used in the 1980's, however its use really only gained popularity a few decades later. In the early days, terms such as environmentally-sensitive or environmentally-responsive polymers, stimuli-reversible or stimuli-sensitive polymers, or polymers with phase transitions have also been used.

Rowan, Stuart J.↗
DOE OSTI2019

Two‐dimensional graphene oxide‐reinforced porous biodegradable polymeric nanocomposites for bone tissue engineering

Abstract This study investigates the mechanical properties and in vitro cytotoxicity of two‐dimensional (2D) graphene oxide nanoribbons and nanoplatelets (GONRs and GONPs) reinforced porous polymeric nanocomposites. Highly porous poly(propylene fumarate) (PPF) nanocomposites were prepared by dispersing 0.2 wt % single‐ and multiwalled SONRs (SWGONRs and MWGONRs) and GONPs. The mechanical properties of scaffolds were characterized using compression testing and in vitro cytocompatibility was assessed using QuantiFlour assay for cellularity and PrestoBlue assay for cell viability. Immunofluorescence was used to assess collagen‐I expression and deposition in the extracellular matrix. Porous PPF scaffolds were used as a baseline control and porous single and multiwalled carbon nanotubes (SWCNTs and MWCNTs) reinforced nanocomposites were used as positive controls. Results show that incorporation of 2D graphene nanomaterials leads to an increase in the mechanical properties of porous PPF nanocomposites with following the trend: MWGONRs > GONPs > SWGONRs > MWCNTs > SWCNTs > PPF control. MWGONRs showed the best enhancement of compressive mechanical properties with increases of up to 26% in compressive modulus (i.e., Young's modulus), ~60% in yield strength, and ~24% in the ultimate compressive strength. Addition of 2D nanomaterials did not alter the cytocompatibility of porous PPF nanocomposites. Furthermore, PPF nanocomposites reinforced with SWGONRs, MWGONRs, and GONPs show an improvement in the adsorption of collagen‐I compared to PPF baseline control. The results of this study show that 2D graphene nanomaterial reinforced porous PPF nanocomposites possess superior mechanical properties, cytocompatibility, and increased protein adsorption. The favorable cytocompatibility results opens avenues for in vivo safety and efficacy studies for bone tissue engineering applications. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1143–1153, 2019.

Farshid, Behzad↗
DOE OSTI2018

An Efficient Post-Polymerization Modification of Poly(Styrene- co -Maleic Anhydride) for Thermally Reversible Nanocomposites

A copolymer of maleic anhydride and styrene is functionalized with Diels–Alder (DA) capable pendant groups to enable the study of this material with different crosslink densities. This constituent is synthesized using commercially available starting materials and relatively simple and uncomplicated chemistries which open the possibility for its use in large-scale applications. The 10%, 25%, 50%, and 100% DA nominal crosslinking based on available pendant furan groups on the polymeric component is investigated. The reaction kinetics are monitored using infrared spectroscopy and rheology. Based on the rheological results, carbon nanotube (CNT) incorporation into the DA matrix is explored in order to determine its effects on the complex modulus of the material. This work done in this report is meant as a proof of concept for this DA material with the possibility of its incorporation into other commonly used bulk materials and/or adhesives to allow for an easily reversible product formulation.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Durability of polymeric encapsulation materials in a PMMA/glass concentrator photovoltaic system

We examined the durability of polymeric encapsulation materials using outdoor exposure at the nominal geometric concentration of 500 suns. The results for 36-month cumulative field deployment are presented for materials including: poly(ethylene-co-vinyl acetate), (EVA); polyvinyl butyral (PVB); ionomer; polyethylene/polyoctene copolymer (PO); thermoplastic polyurethane (TPU); poly(dimethylsiloxane) (PDMS); poly(diphenyl dimethyl siloxane) (PDPDMS); and poly(phenyl-methyl siloxane) (PPMS). Measurements of the field conditions including ambient temperature and ultraviolet (UV) dose were recorded at the test site during the experiment. Our measurements for the experiment included optical transmittance (with subsequent analysis of solar-weighted transmittance, UV cut-off wavelength, and yellowness index), mass, visual photography, photoelastic imaging, and fluorescence spectroscopy. While the results to date for EVA are presented and discussed, examination here focuses more on the siloxane materials. A specimen recently observed to fail by thermal decomposition is discussed in terms of the implementation of the experiment as well as its fluorescence signature, which was observed to become more pronounced with age. Modulated thermogravimetry (allowing determination of the activation energy of thermal decomposition) was performed on a subset of the siloxanes to quantify the propensity for decomposition at elevated temperatures. Supplemental, Pt-catalyst- and primer-solutions as well as peroxide-cured PDMS specimens were examined to assess the source of the luminescence. Furthermore, our results, including the change in optical transmittance, observed failure modes, and subsequent analyses of the failure modes are described in the conclusions.

14 SOLAR ENERGY↗
DOE OSTI2020

Round-robin weathering test of various polymeric back-sheets for PV modules with different ultraviolet irradiation and sample temperatures

Durability assessment of materials exposed to natural weathering with expected service lifetimes of more than 20 years requires accelerated testing of the UV stability, especially for polymeric materials. Fraunhofer ISE organized an interlaboratory comparison for testing different back-sheets in various test laboratories using different UV sources. The five participating test laboratories used three different types of UV sources. The interaction of the UV radiation with the polymers used in PV modules is main subject of this round-robin. Laminates were produced by using solar glass and a suitable EVA encapsulant combined with 10 different back-sheets. The simultaneous usage of different optical filters allowed to investigate roughly the spectral sensitivity and the intensity impact. The degradation was followed by spectral reflectance and transmittance measurements and calculation of the yellowness index as degradation indicator. Clear differences in the degradation behavior of the different products were found.

14 SOLAR ENERGY↗