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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

Crosslinking Amine-Modified Silica Aerogels with Epoxies: Mechanically Strong Lightweight Porous Materials

The mesoporous surfaces of TMOS-derived silica aerogels have been modified with amines by co-polymerization of TMOS with APTES. The amine sites have become anchors for crosslinking the nanoparticles of the skeletal backbone of the aerogel by attachment of di-, tri and tetra-functional epoxies. The resulting conformal coatings increase the density of the native aerogels by a factor of 2-3 but the strength of the resulting materials may increase by more than two orders of magnitude. Processing variables such as amount of APTES used to make the gels, the epoxy type and concentration used for crosslinking, as well as the crosslinking temperature and time were varied according to a multivariable design-of-experiments (DOE) model. It was found that while elastic modulus follows a similar trend with density, maximum strength is attained neither at the maximum density nor at the highest concentration of -NH2 groups, suggesting surface saturation effects. Aerogels crosslinked with the tri-functional epoxide always show improved strength compared with aerogels crosslinked with the other two epoxides under identical conditions. Solid C-13 NMR studies show residual unreacted epoxides, which condense with ne another by heating crosslinked aerogels at 150 C.

Meador, Mary Ann B.↗
DOE OSTI2020

Solution–Processable Thermally Crosslinked Organic Radical Polymer Battery Cathodes

Organic radical polymers are promising cathode materials for next-generation batteries because of their rapid charge transfer and high cycling stability. However, these organic polymer electrodes gradually dissolve in the electrolyte, resulting in capacity fade. Several crosslinking methods have been developed to improve the performance of these electrodes, but they are either not compatible with carbon additives or compromise the solution processability of the electrodes. A one-step post-synthetic, carbon-compatible crosslinking method was developed to effectively crosslink an organic polymer electrode and allow for easy solution processing. The highest electrode capacity of 104 mAh g –1 (vs. a theoretical capacity of 111 mAh g –1 ) is achieved by introducing 1 mol % of the crosslinker, whereas the highest capacity retention (99.6 %) is obtained with 3 mol % crosslinker. In addition, mass transfer was observed in situ by using electrochemical quartz crystal microbalance with dissipation monitoring. Furthermore, these results may guide future electrode design toward fast-charging and high-capacity organic electrodes.

25 ENERGY STORAGE↗
DOE OSTI2020

Use of high throughput screening methods to study dual-functional crosslinkable latexes

Herein, structure-formulation-property relationships for crosslinkable core-shell latexes were studied initially using high throughput screening methods and then using conventional experimental methods to determine optimum coating formulations. Two approaches that are used within coatings technology to improve sustainability are reduction in volatile organic compounds (VOC) and reduction in energy needed to cure coatings. Hybrid crosslinkable core-shell latexes have shown potential in meeting these challenges where film properties provided by particle coalescence are not sufficient and chemical crosslinking is needed. However, with numerous parameters involved such as latex particle architecture, nature and amount of crosslinker, and curing conditions, the screening of formulations via conventional coating testing methods becomes laborious and time-consuming. The results from high-throughput dye extraction and puncture testing were compared to data from conventional testing methods such as chemical resistance (MEK double rubs), pendulum hardness, and tensile testing to identify correlations. The dye extraction results have shown a strong correlation to solvent resistance and pendulum hardness data whereas toughness from puncture testing data correlated to tensile testing. Both high throughput dye extraction and puncture testing methods can be used for the accelerated screening of crosslinkable coating formulations to optimize curing parameters to achieve the best coating performance.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Structure and in vivo psoralen DNA crosslink repair activity of mycobacterial Nei2

Mycobacterium smegmatis Nei2 is a monomeric enzyme with AP β-lyase activity on single-stranded DNA. Expression of Nei2, and its operonic neighbor Lhr (a tetrameric 3'-to-5' helicase), is induced in mycobacteria exposed to DNA damaging agents. Here, we find that nei2 deletion sensitizes M. smegmatis to killing by DNA inter-strand crosslinker trimethylpsoralen but not to crosslinkers mitomycin C and cisplatin. By contrast, deletion of lhr sensitizes to killing by all three crosslinking agents. We report a 1.45 Å crystal structure of recombinant Nei2, which is composed of N and C terminal lobes flanking a central groove suitable for DNA binding. The C lobe includes a tetracysteine zinc complex. Mutational analysis identifies the N-terminal proline residue (Pro2 of the ORF) and Lys51, but not Glu3, as essential for AP lyase activity. We find that Nei2 has 5-hydroxyuracil glycosylase activity on single-stranded DNA that is effaced by alanine mutations of Glu3 and Lys51 but not Pro2. Testing complementation of psoralen sensitivity by expression of wild-type and mutant nei2 alleles in Δnei2 cells established that AP lyase activity is neither sufficient nor essential for crosslink repair. By contrast, complementation of psoralen sensitivity of Δlhr cells by mutant lhr alleles depended on Lhr’s ATPase/helicase activities and its tetrameric quaternary structure. The lhr–nei2 operon comprises a unique bacterial system to rectify inter-strand crosslinks.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Photo-Crosslinkable Naphthalene Diimide Polymer for Solution-Processed n – i – p Perovskite Solar Cells

We copolymerize a norbornene monomer bearing a pendant naphthalene diimide with a norbornene bearing a cinnamate pendant moiety to synthesize a crosslinkable electron-transporting polymer and study its use in solution-processed n–i–p perovskite solar cells. The crosslinked material exhibits over 90% transparency in the visible region and higher thermal stability (>300 °C) and lower surface energy than the corresponding homopolymer of the naphthalene diimide functionalized norbornene. Coating an ITO surface with the photo-crosslinked copolymer yields a slightly lower work function than homopolymer-coated ITO. We show that the morphologies of the perovskite films deposited on both polymers are similar (~300 nm features) based upon scanning electron microscopy. Our solar-cell device results show that the crosslinked naphthalene diimide polymer gives a higher open-circuit voltage (1.08 vs 1.05 V), fill factor (average 64.43 vs 58.77%), and stabilized power conversion efficiency (12.28 vs 10.33%) compared to its non-crosslinked homopolymer counterpart, as well as reduced hysteresis. As a result, we attribute the improved performance to decreased work function, reduced nonradiative recombination, and higher shunt resistance.

14 SOLAR ENERGY↗
DOE OSTI2023

Post-Hydration Crosslinking of Ion Exchange Membranes to Control Water Content

The utilization of crosslinking as a technique to limit excess water uptake in ion exchange membranes is a well-established approach. However, traditional methods involve performing the crosslinking reaction before the membrane self-segregates into hydrophilic and hydrophobic domains upon exposure to water. In this study, we employ numerical and molecular simulations to explore the potential of post-hydration crosslinking of the polymer at subsaturated conditions. This process allows for the development of a nanosegregated morphology, which establishes well-connected but narrow water channels, while limiting additional sorption of water. The significant reduction in membrane swelling observed in our study indicates that post-hydration crosslinking could be a promising approach to regulate water uptake in ion exchange membranes. Here based on our analyses, we propose chemical crosslinking strategies that may yield high membrane gel fractions.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Well-designed Crosslinked Polymer Electrolyte Enables High Ionic Conductivity and Enhanced Salt Solvation

A new facile single-step method to fabricate crosslinked polymer electrolyte membranes consisting of branched poly(ethyleneimine), (PEI) and poly(ethylene oxide), (PEO) is demonstrated. The membranes exhibit excellent ionic conductivity (1.2 × 10 –3 S cm –1 at 80 °C) with minimal addition of plasticizer (20 wt%). The amine functional group in the PEI-PEO crosslinked matrix provides Lewis basic and hydrogen bonding characteristics that facilitate the dissolution of lithium salt and enables a higher cation transport number than a PEO crosslinked matrix. The glass transition temperature, degree of crystallinity, and room temperature storage modulus increases with decreasing crosslink density and increasing ratio of free amines. The resultant ionic conductivity and mechanical strength can be flexibly tailored by varying the molar ratio of free amine moieties in the crosslinked PEI-PEO matrix. This study provides an improved synthesis method, in-depth characterization, and fundamental insights on the effect of free amine moieties on the transport properties of a highly conductive gel polymer electrolyte.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Ion Transport in Concentrated Crosslinked Solid Polymer Electrolytes

Crosslinking polymers is a common approach to create mechanically stable solid materials such as polymer electrolytes for lithium batteries. In conventional liquid electrolytes, the solvent molecules move freely to accommodate the field-induced motion of ions. However, in crosslinked polymer electrolytes, the rearrangement of polymer segments is constrained by the deformation limits of the network. Herein, we develop a new transport model that accounts for both the formation of concentration gradients and the elasticity of the electrolyte. The elasticity is incorporated by adding an additional term related to the entropy of crosslinked strands to the electrochemical potential of the salt. The resulting Crosslink Model contains two adjustable parameters: $\mathcal{N}$, the average number of monomers in a strand, and λ crit , the maximum strain the network can sustain. These solid-like constraints produce singularities in the governing transport equations, fundamentally altering the concentration profiles. Plateaus in salt concentrations emerge near the electrodes, and network elasticity introduces a strain overpotential. When compared to a Baseline Model ($\mathcal{N}$ → ∞, equivalent to concentrated solution theory), which predicts steepest gradients near the electrodes, both models yield similar current–voltage relationships. Model predictions are compared to electrochemical data for a poly(ethylene oxide)-based crosslinked polymer electrolyte.

Patel, Vivaan [University of California, Berkeley,↗
DOE OSTI2022

Crosslink V.0.11.x User Manual

CrossLink is a novel two-dimensional and three-dimensional geometry and mesh generation software package developed by the Simulation Tools team at Los Alamos National Laboratory. This software represents the third generation of topology-based mesh generation technology developed by the Department of Defense and the Department of Energy with a special focus on complex multi-material hydrodynamic applications, mesh scalability, and high-order element mesh generation. The topology-based meshing approach offered by CrossLink enables users to quickly and easily mesh complex geometries in a repeatable and robust manner. CrossLink’s topology-based meshing approach is well-suited for parametric design studies, parametric design optimization, damage scenario assessment, and iterative design modification (i.e. feature addition and/or removal). CrossLink’s python API allows workflow scripting of the geometry creation and mesh generation process for traceability, repeatability, data provenance, and version control. CrossLink consists of three main components: a graphical user interface (GUI), a geometry creation and mesh generation engine, and a python API that provides a workflow scripting interface to the geometry and meshing functions.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1987

Crosslinking-property relationships in PMR polyimide composites. I

The thermooxidatively-induced crosslinking/ physical and mechanical property relationships of graphite fiber-reinforced PMR polyimide-matrix composites were studied during isothermal exposure of the composite specimens at 288 C in air for periods of up to 5000 hr. The crosslinking densities due to this treatment were estimated on the basis of the kinetic theory of rubber elasticity and shifts in the glass transition temperature T(g). Several linear relationships are noted between crosslink density and physical and mechanical properties: T(g), initial weight loss, and elevated temperature interlaminar shear strength increase with crosslink density, while initial moisture absorption decreases. After achieving the highest crosslink density, several of the composite properties begin to decrease from their maximum values.

Pater, R. H.↗
NASA NTRS1990

Process for crosslinking methylene-containing aromatic polymers with ionizing radiation

A process for crosslinking aromatic polymers containing radiation-sensitive methylene groups (-CH2-) by exposing the polymers to ionizing radiation thereby causing crosslinking of the polymers through the methylene groups is described. Crosslinked polymers are resistant to most organic solvents such as acetone, alcohols, hydrocarbons, methylene, chloride, chloroform, and other halogenated hydrocarbons, to common fuels and to hydraulic fluids in contrast to readily soluble uncrosslinked polymers. In addition, the degree of crosslinking of the polymers depends upon the percentage of the connecting groups which are methylene which ranges from 5 to 50 pct and preferably from 25 to 50 pct of the connecting groups, and is also controlled by the level of irradiation which ranges from 25 to 1000 Mrads and preferably from 25 to 250 Mrads. The temperature of the reaction conditions ranges from 25 to 200 C and preferably at or slightly above the glass transition temperature of the polymer. The crosslinked polymers are generally more resistant to degradation at elevated temperatures such as greater than 150 C, have a reduced tendency to creep under load, and show no significant embrittlement of parts fabricated from the polymers.

Bell, Vernon L.↗
NASA NTRS1992

Platelet factor XIII increases the fibrinolytic resistance of platelet-rich clots by accelerating the crosslinking of alpha 2-antiplasmin to fibrin

Platelet clots resist fibrinolysis by plasminogen activators. We hypothesized that platelet factor XIII may enhance the fibrinolytic resistance of platelet-rich clots by catalyzing the crosslinking of alpha 2-antiplasmin (alpha 2AP) to fibrin. Analysis of plasma clot structure by polyacrylamide gel electrophoresis and immunoblotting revealed accelerated alpha 2AP-fibrin crosslinking in platelet-rich compared with platelet-depleted plasma clots. A similar study of clots formed with purified fibrinogen (depleted of factor XIII activity), isolated platelets, and specific factor XIII inhibitors indicated that this accelerated crosslinking was due to the catalytic activity of platelet factor XIII. Moreover, when washed platelets were aggregated by thrombin, there was evidence of platelet factor XIII-mediated crosslinking between platelet alpha 2AP and platelet fibrin(ogen). Specific inhibition (by a monoclonal antibody) of the alpha 2AP associated with washed platelet aggregates accelerated the fibrinolysis of the platelet aggregate. Thus in platelet-rich plasma clots, and in thrombin-induced platelet aggregates, platelet factor XIII actively formed alpha 2AP-fibrin crosslinks, which appeared to enhance the resistance of platelet-rich clots to fibrinolysis.

Non-NASA Center↗
DOE OSTI2025

Crosslinked polymeric ionic liquid stationary phases incorporating a combination of silver(I) and copper(II) ions for olefin separations by gas chromatography

The development of efficient and selective olefin separation technologies is a critical challenge within the chemical industry given the high energy demands of conventional cryogenic distillation methods. To address this, the study explores the effectiveness of polymeric ionic liquid (PIL) stationary phases in gas chromatography (GC) that incorporate both silver(I) ([Ag + ]) and copper(II) ([Cu 2+ ]) ions for enhanced olefin separation via π-complexation interactions. Further, the effects of both non-crosslinked and crosslinked PIL stationary phases containing varying ratios of [Ag⁺] and [Cu²⁺] ions were systematically investigated to evaluate their impact on the separation of olefins from paraffins and structurally similar olefins. Retention measurements using a broad range of olefinic probes revealed that [Ag⁺] ions provided stronger and more consistent π-complexation in PIL-based stationary phases, while [Cu²⁺] ions preferentially enhance olefin retention in crosslinked systems. Furthermore, thermal stability studies showed that [Ag + ]-containing PIL stationary phases maintain stable olefin separation efficiency over prolonged exposure under elevated temperatures, while crosslinked PIL stationary phases containing [Cu 2+ ] ions exhibited stronger retention due to increased surface adsorption. These findings provide insight into the tunability of metal–olefin interactions using PIL-based stationary phases and suggest design strategies for achieving thermally stable and highly selective chromatographic separations of unsaturated hydrocarbons.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Site-specific photo-crosslinking in a double crossover DNA tile facilitated by squaraine dye aggregates: advancing thermally stable and uniform DNA nanostructures

We investigated the role of dichloro-squaraine (SQ) dye aggregates in facilitating thymine–thymine interstrand photo-crosslinking within double crossover (DX) tiles, to develop thermally stable and structurally uniform two-dimensional (2D) DNA-based nanostructures. By strategically incorporating SQ modified thymine pairs, we enabled site-selective [2 + 2] photocycloaddition under 310 nm UV light. Strong dye–dye interactions, particularly through the formation of aggregates, facilitated covalent bond formation between proximal thymines. To evaluate the impact of dye aggregation on crosslinking efficiency, ten DX tile variants with varying SQ-modified thymine positions were tested. Our results demonstrated that SQ dye aggregates significantly enhanced crosslinking, driven by precise SQ-modified thymine dimer placement within the DNA tiles. Analytical techniques, including denaturing PAGE and UV-visible spectroscopy, validated successful crosslinking in DNA tiles with multiple SQ-modified thymine pairs. This non-phototoxic method offers a potential route for creating thermally stable, homogeneous higher-order DNA–dye assemblies with potential applications in photoactive and exciton-based fields such as optoelectronics, nanoscale computing, and quantum computing. Furthermore, the insights from this study establish a foundation for further exploration of advanced DNA–dye systems, enabling the design of next-generation DNA nanostructures with enhanced functional properties.

2D DNA template↗
DOE OSTI2020

Reversible Crosslinked Polymer Binder for Recyclable Lithium Sulfur Batteries with High Performance

Owing to the negative impact of the extensive utilization of batteries on the environment, sustainability of the cells needs to be included in the systemic research of batteries. In this work, a dissolvable ionic crosslinked polymer (DICP) is exploited as a binder for lithium–sulfur batteries by crosslinking the polyacrylic acid and polyethyleneimine through carboxy-amino ionic interaction. This interaction is pH-controlled, and therefore, the crosslinked binder network can be readily dissociated under basic conditions, providing a facile strategy enabling valuable components recycled through a convenient washing method. The sulfur cathode prepared using the recycled carbon–sulfur composite can deliver comparable capacity as that of fresh electrode. In addition, evidence from cell performance and characterizations, such as in situ X-ray absorption spectroscopy, in situ UV–visible spectroscopy, X-ray photoelectron spectroscopy, and density functional theory calculation, confirms that DICP is a more effective binder than its commercial counterpart on suppressing polysulfide dissolution in the electrolyte. Exploiting reversible crosslinked polymer binder for recyclable Li–S batteries with ameliorated electrochemical performance, this study illuminates sustainable development for large-scale energy storage systems.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Tailoring polyvinyl alcohol-sodium alginate (PVA-SA) hydrogel beads by controlling crosslinking pH and time

Abstract Hydrogel-encapsulated catalysts are an attractive tool for low-cost intensification of (bio)-processes. Polyvinyl alcohol-sodium alginate hydrogels crosslinked with boric acid and post-cured with sulfate (PVA-SA-BS) have been applied in bioproduction and water treatment processes, but the low pH required for crosslinking may negatively affect biocatalyst functionality. Here, we investigate how crosslinking pH (3, 4, and 5) and time (1, 2, and 8 h) affect the physicochemical, elastic, and process properties of PVA-SA-BS beads. Overall, bead properties were most affected by crosslinking pH. Beads produced at pH 3 and 4 were smaller and contained larger internal cavities, while optical coherence tomography suggested polymer cross-linking density was higher. Optical coherence elastography revealed PVA-SA-BS beads produced at pH 3 and 4 were stiffer than pH 5 beads. Dextran Blue release showed that pH 3-produced beads enabled higher diffusion rates and were more porous. Last, over a 28-day incubation, pH 3 and 4 beads lost more microspheres (as cell proxies) than beads produced at pH 5, while the latter released more polymer material. Overall, this study provides a path forward to tailor PVA-SA-BS hydrogel bead properties towards a broad range of applications, such as chemical, enzymatic, and microbially catalyzed (bio)-processes.

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

Viscoelastic behavior of polymers undergoing crosslinking reactions.

Previously a method was developed for predicting the viscoelastic response of polymers undergoing scission reactions. These results are now extended to include crosslinking reactions. As for scission, at any given time the character of the network chains is determined by the instantaneous crosslink density. For scission all chains were assumed to carry the same stress; for crosslinking, however, the stress is distributed between the 'new' and 'old' chains. Equations for calculating the creep response of a system which experiences a step increase in crosslink density are derived.

Moacanin, J.↗
NASA NTRS1974

Effect of crosslinking density on biaxial relaxation of SBR by using reduced variables

The use of reduced variables to account for the effect of crosslinking density in a styrene-butadiene rubber (SBR) system is demonstrated for general biaxial stress states. Recently published results from stress relaxation tests on five SBR vulcanizates crosslinked to different degrees by tetramethylthiuram disulfide were superposed by using the crosslinking density as a reduction variable. The equilibrium shear modulus calculated from the master relaxation curve at long reduced times was in satisfactory agreement with other results for SBR. The time-axis shifts were related in a linear logarithmic manner to the crosslinking density but had a slope slightly less than values previously reported for elastomer systems.

Arenz, R. J.↗