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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 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Damage to Polystyrene Polymer Film by Shock Wave Induced Bubble Collapse

Metallic surfaces that are in contact with solutions are commonly used in numerous applications where these surfaces can be damaged by shock wave induced bubble collapse. Use of polymer films that coat such surfaces to prevent them from damage requires a better understanding of how much harm collapsing bubbles produce in the films. In this study, we report the results from coarse-grained molecular dynamics simulations to study the damage to polystyrene (PS) films coating a hard surface. The damage was caused by a collapsing nanobubble located in the proximity of the film and interacting with an impinging shock wave. This collapse produces a high-speed water jet that impacts the PS film with a greater force than the shock front and creates cavities/pits in the PS film. We observed that polymer molecules located in the jet vicinity undergo conformational extension in the direction perpendicular to the jet motion, while chain molecules in the rest of the film undergo compression. Furthermore, we also observed that damage to the film is sensitive to the strength of the shock wave.

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

Preparation and characterization of aminated co-solvent enhanced lignocellulosic fractionation lignin as a renewable building block for the synthesis of non-isocyanate polyurethanes

Lignin is a major bioresource from 2nd generation biorefinery process streams and from pulp and paper production that is still severely underutilized nowadays. Its natural polymeric and aromatic structures make it suitable as a potential building block for biopolymer production. Due to the growing environmental and health concerns over conventional polyurethane (PU) manufacturing processes that utilize toxic isocyanates, there is a great interest to develop a non-isocyanate PU (NIPU) route. Herein, we demonstrate a novel strategy that uses highly pure lignin isolated from co-solvent enhanced lignocellulosic fractionation (CELF) pretreatment of poplar wood to produce biobased NIPUs. In this strategy, hardwood poplar is firstly fractionated via a CELF pretreatment to produce a clean lignin stream that is rich in phenolics. The CELF lignin was then aminated by a Mannich reaction, and the aminated CELF lignin was finally reacted with bicyclic carbonates to yield an advanced NIPU. In this work, the structure, mechanical, and thermal properties of these novel NIPUs were elucidated by FTIR, NMR, tensile test, dynamic mechanical analysis (DMA), and thermogravimetric analysis (TGA). The mechanical properties of these lignin based NIPUs could be tuned from highly rigid to elastic polymers by simply modifying the lignin constituents of the polymer. The thermal stabilities of NIPUs were improved because of the addition of aminated lignin, and NIPU containing 55 and 23 wt% lignin showed the highest tensile strength (~1.2 MPa) and elongation at break (~140%), respectively. The results obtained in this study demonstrate that the reaction of cyclic carbonate with aminated lignin represents an interesting pathway for the synthesizing of lignin based NIPU with a relative high lignin content.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Determining the influence of temperature and pressure on the structural stability in a polyurea elastomer

The structural response of amorphous elastomers to applied pressure and temperature is of significant interest given their potential for blast and impact protection applications. While understanding disordered structures is often challenging, this study focuses on the ordered correlations that are present at the atomic level even in amorphous materials. This local order was characterized in polyurea elastomers with two molecular weights up to 6 GPa and ~280 °C using in situ energy dispersive X-ray diffraction at the Advanced Photon Source via total scattering techniques. The resulting structure factors and pair distribution functions indicate that the applied pressure reduced the free volume but had little effect on covalent bonds for both molecular weights. Temperature-induced order-disorder transitions that occur readily at ambient pressures within the temperature range studied here were not observed, their onset likely delayed by the limited chain mobility associated with the free volume reduction. In conclusion, this study demonstrates that total scattering offers insights into the high-pressure structure of disordered polymers that are otherwise inaccessible using more conventional X-ray scattering techniques.

42 ENGINEERING↗
DOE OSTI2020

Nonlinear propagating modes beyond the phonons in fluorite-structured crystals

The vibrational energy of crystals is known to propagate in a fixed number of phonon branches allowed by symmetry. In the realm of nonlinear dynamics, however, additional nonlinear propagating modes are possible. Nonlinear propagating modes have unique properties that are important in many disciplines including optical communications, conducting polymers, biology, magnetism, and nuclear physics. Yet, despite the crucial importance of crystal lattice vibrations in fundamental and applied science, such additional propagating modes have not been observed in ordinary crystals. Here, we show that propagating modes exist beyond the phonons in fluorite-structured thoria, urania, and natural calcium fluoride using neutron scattering and first-principles calculations. These modes are observed at temperatures ranging from 5 K up to 1200 K, extend to frequencies 30–40% higher than the maximum phonon frequency, and travel at velocities comparable to or higher than the fastest phonon. The nonlinear origin of the modes is explained in part via perturbation theory, which approximately accounts for nonlinearity. Given that these modes are still clearly observed at 5 K, they are likely an inherent feature of the quantum ground state. The existence of these waves in three-dimensional crystals may have ramifications for material properties.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Nanoscale resolution of microbial fiber degradation in action

The lives of microbes unfold at the micron scale, and their molecular machineries operate at the nanoscale. Their study at these resolutions is key toward achieving a better understanding of their ecology. We focus on cellulose degradation of the canonical Clostridium thermocellum system to comprehend how microbes build and use their cellulosomal machinery at these nanometer scales. Degradation of cellulose, the most abundant organic polymer on Earth, is instrumental to the global carbon cycle. We reveal that bacterial cells form ‘cellulosome capsules’ driven by catalytic product-dependent dynamics, which can increase the rate of hydrolysis. Biosynthesis of this energetically costly machinery and cell growth are decoupled at the single-cell level, hinting at a division-of-labor strategy through phenotypic heterogeneity. This novel observation highlights intrapopulation interactions as key to understanding rates of fiber degradation.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Cost-effective carbon fiber precursor selections of polyacrylonitrile-derived blend polymers: carbonization chemistry and structural characterizations

Blending polyacrylonitrile (PAN) with plastic wastes and bio-based polymers provides a convenient and inexpensive method to realize cost-effective carbon fiber (CF) precursors. In this work, PAN-based blend precursors are investigated using ReaxFF reactive molecular dynamics simulations with respect to the formation of all-carbon rings, the evolutions of oxygen-containing and nitrogen-containing species, and the migration of carbon atoms to form turbostratic graphene. From these simulations, we identify that PAN/cellulose (CL) blend manifests the highest carbon yield and the most substantial all-carbon ring formation. This ReaxFF-based finding is confirmed by Raman and TEM experiments indicating high crystallinity for PAN/CL-derived blend CFs. We trace the pathway of gasification and carbonization of PAN/CL to elaborate the mechanism of the formation of all-carbon ring networks. We discover that the acetals of CL can catalyze the cyclization of the blend precursor, allowing for the search for CL derivatives or the other kinds of bio-based polymers with similar functionalities as alternative blends. In addition, we examine the structural characteristics using the carbon–carbon (C–C) radial distribution functions, C–C bond length distributions, and sp2 C atom ratios for the four representative precursors, i.e., PAN, oxidized PAN, PAN/nylon 6,6, and PAN/CL. Our simulation results show the most extensive all-carbon ring cluster and graphitic structure growths for PAN/CL. Here, we propose PAN/CL as a cost-effective alternative CF precursor, since (a) CL is naturally abundant and eco-friendly for production, (b) the blend precursor PAN/CL does not require oxidation treatment, (c) PAN/CL has a high carbon yield with substantial all-carbon ring formation, and (d) PAN/CL based CFs potentially provide a mechanical property enhancement.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Development of Coarse-Grained Models for Poly(4-vinylphenol) and Poly(2-vinylpyridine): Polymer Chemistries with Hydrogen Bonding

In this paper, we identify the modifications needed in a recently developed generic coarse-grained (CG) model that captured directional interactions in polymers to specifically represent two exemplary hydrogen bonding polymer chemistries—poly(4-vinylphenol) and poly(2-vinylpyridine). We use atomistically observed monomer-level structures (e.g., bond, angle and torsion distribution) and chain structures (e.g., end-to-end distance distribution and persistence length) of poly(4-vinylphenol) and poly(2-vinylpyridine) in an explicitly represented good solvent (tetrahydrofuran) to identify the appropriate modifications in the generic CG model in implicit solvent. For both chemistries, the modified CG model is developed based on atomistic simulations of a single 24-mer chain. This modified CG model is then used to simulate longer (36-mer) and shorter (18-mer and 12-mer) chain lengths and compared against the corresponding atomistic simulation results. We find that with one to two simple modifications (e.g., incorporating intra-chain attraction, torsional constraint) to the generic CG model, we are able to reproduce atomistically observed bond, angle and torsion distributions, persistence length, and end-to-end distance distribution for chain lengths ranging from 12 to 36 monomers. We also show that this modified CG model, meant to reproduce atomistic structure, does not reproduce atomistically observed chain relaxation and hydrogen bond dynamics, as expected. Simulations with the modified CG model have significantly faster chain relaxation than atomistic simulations and slower decorrelation of formed hydrogen bonds than in atomistic simulations, with no apparent dependence on chain length.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Enhancing ion transport in charged block copolymers by stabilizing low symmetry morphology: Electrostatic control of interfaces

Recently, the interest in charged polymers has been rapidly growing due to their uses in energy storage and transfer devices. Yet, polymer electrolyte-based devices are not on the immediate horizon because of the low ionic conductivity. In the present study, we developed a methodology to enhance the ionic conductivity of charged block copolymers comprising ionic liquids through the electrostatic control of the interfacial layers. Unprecedented reentrant phase transitions between lamellar and A15 structures were seen, which cannot be explained by well-established thermodynamic factors. X-ray scattering experiments and molecular dynamics simulations revealed the formation of fascinating, thin ionic shell layers composed of ionic complexes. The ionic liquid cations of these complexes predominantly presented near the micellar interfaces if they had strong binding affinity with the charged polymer chains. Therefore, the interfacial properties and concentration fluctuations of the A15 structures were crucially dependent on the type of tethered acid groups in the polymers. Overall, the stabilization energies of the A15 structures were greater when enriched, attractive electrostatic interactions were present at the micellar interfaces. Contrary to the conventional wisdom that block copolymer interfaces act as “dead zone” to significantly deteriorate ion transport, this study establishes a prospective avenue for advanced polymer electrolyte having tailor-made interfaces.

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

Reprocessable polyhydroxyurethane networks reinforced with reactive polyhedral oligomeric silsesquioxanes (POSS) and exhibiting excellent elevated temperature creep resistance

The rapid development of covalent adaptable networks or vitrimers shows promise for addressing the long-standing recycling issues associated with conventional, permanently cross-linked thermosets. At the same time, it is important to demonstrate that properties of reprocessable polymer networks can be optimized to meet the ongoing demand for high-performance materials. We have fabricated reprocessable polyhydroxyurethane (PHU) network composites reinforced with reactive polyhedral oligomeric silsesquioxanes (POSS). With functionalized POSS serving as a fraction of the cross-linkers, the PHU–POSS network nanocomposites exhibit significantly enhanced storage modulus at the rubbery plateau region relative to the neat PHU network. With up to 10 wt% POSS loading, these network composites can undergo melt-state reprocessing at 140 °C with 100% property recovery associated with cross-link density. We also show that hydroxyurethane dynamic chemistry leads to excellent creep resistance at elevated temperature up to 90 °C and is unaffected by reactive incorporation of POSS. In conclusion, this study demonstrates the effectiveness of POSS as nanofillers for designing high-performance, organic-inorganic dynamic PHU networks with excellent reprocessability.

42 ENGINEERING↗
DOE OSTI2020

Recycling Epoxy by Vitrimerization: Influence of an Initial Thermoset Chemical Structure

Epoxy/anhydride cured thermosets are widely used in aerospace and wind energy structures. Recycling the enormous amounts of epoxy thermoset waste remains a global challenge. Vitrimerization, a practical, low-cost, eco-friendly and scalable method was developed for closed-loop recycling of the crosslinked epoxy by converting the permanent network into a vitrimer type dynamic network. Here we study the effect of virgin epoxy network properties on network reforming efficiency and the activation energy of the dynamic network by varying the epoxy/anhydride ratio. The results point out that the permanent network crosslink density and glass transition temperature have a more pronounced effect on vitrimerization efficiency by comparison with the concentration of free hydroxyl groups in the system. Furthermore, the result can be potentially used to better control vitrimerization efficiency in recycling epoxy thermoset polymers and tailor the vitrimerized products properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Rational Enzyme Design for Controlled Functionalization of Acetylated Xylan for Cell-Free Polymer Biosynthesis

Xylan O-acetyltransferase 1 (XOAT1) is involved in O-acetylating the backbone of hemicellulose xylan. Recent structural analysis of XOAT1 showed two unequal lobes forming a cleft that is predicted to accommodate and position xylan acceptors into proximity with the catalytic triad. Here, we used docking and molecular dynamics simulations to investigate the optimal orientation of xylan in the binding cleft of XOAT1 and identify putative key residues (Gln445 and Arg444 on Minor lobe & Asn312, Met311 and Asp403 on Major lobe) involved in substrate interactions. Site-directed mutagenesis coupled with biochemical analyses revealed the major lobe of XOAT1 is important for xylan binding. Mutation of single key residues yielded XOAT1 variants with various enzymatic efficiencies that are applicable to one-pot synthesis of xylan polymers with different degrees of O-acetylation. Taken together, our results demonstrate the effectiveness of computational modeling in guiding enzyme engineering aimed at modulating xylan and redesigning plant cell walls.

93 SC - Biological and Environmental Research (BER↗
DOE OSTI2020

Viscoelastic Response of Dispersed Entangled Polymer Melts

Any polymer synthesis routes result in molecular weight dispersity DAI, depending on the polymerization mechanism. The lowest dispersity polymers are those made by anionic and atom-transfer radical polymerization, which exhibit relatively narrow distributions DM=g,„1A172 — 1.02-1.04. This small divergence from monodispersity results in significant number of molecules that differ in their molecular weight from the average and their impact on the viscoelastic response remains an open question. Here the effects of low dispersity on stress relaxation and shear viscosity of entangled melts are studied using a coarse-grained model for polyethylene. Polymer melts with chain length dispersity set to follow a Schulz-Zimm distribution of Dm = 1.0 — 1.16 for an entangled polyethylene melt using molecular dynamic simulations. The systems were studied to times up to 800 ,us which is beyond the terminal time. These systems are compared to those with binary and ternary distributions. The stress relaxation functions were extracted from the Green-Kubo relation and from stress-strain relaxation following a uniaxial extension. We find on the entanglement time scale, both the mean squared displacement and the stress relaxation are independent of D m . The tube diameter and the rubbery plateau for entangled dynamics do not depend on D m . At longer times, the terminal relaxation time decreases as the faster motion of the shorter chains results in constraint release for the longer chains. Probing this low dispersity regime opens the way to evaluate the degree of dispersity that affects mechanical properties.

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

A Self-Healing, Flowable, Yet Solid Electrolyte Suppresses Li-Metal Morphological Instabilities

In this article, lithium metal (Li 0 ) solid-state batteries encounter implementation challenges due to dendrite formation, side reactions, and movement of the electrode–electrolyte interface in cycling. Notably, voids and cracks formed during battery fabrication/operation are hot spots for failure. Here, a self-healing, flowable yet solid electrolyte composed of mobile ceramic crystals embedded in a reconfigurable polymer network is reported. This electrolyte can auto-repair voids and cracks through a two-step self-healing process that occurs at a fast rate of 5.6 µm h -1 . A dynamical phase diagram is generated, showing the material can switch between liquid and solid forms in response to external strain rates. The flowability of the electrolyte allows it to accommodate the electrode volume change during Li 0 stripping. Simultaneously, the electrolyte maintains a solid form with high tensile strength (0.28 MPa), facilitating the regulation of mossy Li 0 deposition. The chemistries and kinetics are studied by operando synchrotron X-ray and in situ transmission electron microscopy (TEM). Solid-state NMR reveals a dual-phase ion conduction pathway and rapid Li + diffusion through the stable polymer-ceramic interphase. This designed electrolyte exhibits extended cycling life in Li 0 –Li 0 cells, reaching 12 000 h at 0.2 mA cm -2 and 5000 h at 0.5 mA cm -2 . Furthermore, owing to its high critical current density of 9 mA cm -2 , the Li 0 –LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) full cell demonstrates stable cycling at 5 mA cm -2 for 1100 cycles, retaining 88% of its capacity, even under near-zero stack pressure conditions.

25 ENERGY STORAGE↗
DOE OSTI2025

Controlling solvation in conducting redox polymers for selective electrochemical separation of nitrate from wastewater

Selective capture of nitrate from wastewater is crucial for ensuring safe drinking water and promoting resource circularity. This study investigated alkylated polyaniline redox polymers as highly-selective electrosorbents to address this challenge. By controlling polymer solvation properties through synthetic functionalization, poly(N-methylaniline) (PNMA) achieves a nitrate uptake of up to 1.38 mmol g −1 -polymer and a separation factor of 7 over chloride. Poly(N-butylaniline) (PNBA) further enhances selectivity, achieving a separation factor beyond 14 due to increased hydrophobicity. The mechanisms underlying this selectivity are investigated using ab initio molecular dynamics (AIMD) and in-situ electrochemical quartz crystal microbalance (EQCM) studies, which reveal that hydrophobicity reduces chloride binding. A technoeconomic analysis indicates that methylation on PANI reduces nitrate removal costs by 50% compared to non-functionalized PANI, due to enhanced selectivity and uptake, and decreased energy consumption. PNMA electrodes demonstrate practical nitrate selectivity over 20 versus chloride in real wastewater, while avoiding sulfate binding. This study highlights the potential of controlling solvation at electroactive polymers to enhance nitrate selectivity, offering a promising design path for redox-mediated electrochemical separations.

chemical engineering↗
DOE OSTI2021

Complex Relationship between Side-Chain Polarity, Conductivity, and Thermal Stability in Molecularly Doped Conjugated Polymers

Molecularly doped conjugated polymers with polar side chains are an emerging class of conducting materials exhibiting enhanced and thermally stable conductivity. In this work, we study the electronic conductivity (σ) and the corresponding thermal stability of two polythiophene derivatives comprising oligoethylene glycol side chains: one having oxygen attached to the thiophene ring (poly(3-(methoxyethoxyethoxy)thiophene) (P3MEET)) and the other having a methylene spacer between the oxygen and the thiophene ring (poly(3-(methoxyethoxyethoxymethyl)thiophene) (P3MEEMT)). Thin films were vapor-doped with fluorinated derivatives of tetracyanoquinodimethane (FnTCNQ, n = 4, 2, 1) to determine the role of dopant strength (electron affinity) in maximum achievable σ. Specifically, when vapor doping with F 4 TCNQ, P3MEET achieved a substantially higher σ of 37.1 ± 10.1 S/cm compared to a σ of 0.82 ± 0.06 S/cm for P3MEEMT. Structural characterization using a combination of X-ray and optical spectroscopy reveals that the higher degree of conformational order of polymer chains in the amorphous domain upon doping with F 4 TCNQ in P3MEET is a major contributing factor for the higher σ of P3MEET. Additionally, vapor-doped P3MEET exhibited superior thermal stability compared to P3MEEMT, highlighting that the presence of polar side chains alone does not ensure higher thermal stability. Molecular dynamics simulations indicate that the dopant–side-chain nonbond energy is lower in the P3MEET:F 4 TCNQ mixture, suggesting more favorable dopant–side-chain interaction, which is a factor in improving the thermal stability of a polymer/dopant pair. Our results reveal that additional factors such as polymer ionization energy and side-chain–dopant interaction should be taken into account for the design of thermally stable, highly conductive polymers.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Impact of Grafting Density on the Assembly and Mechanical Properties of Self-Assembled Metal–Organic Framework Monolayers

Polymer-grafted metal–organic frameworks (MOFs) can be used to form free-standing self-assembled MOF monolayers (SAMMs). Polymer chains can be introduced onto MOF surfaces through either the ligands or metal nodes using both grafting-to and grafting-from approaches. However, controlling the grafting density of polymer-grafted MOFs has not yet been achieved, because a means to control the density of grafting sites on the MOF surface has not been developed. In this study, the grafting density of polymer-grafted UiO-66 (UiO = University of Oslo) was controlled by functionalizing a portion of the Zr(IV) secondary building units (SBUs) on a UiO-66 surface with a so-called blocking agent. The remaining sites on the UiO-66 SBUs were functionalized with polymerization initiation groups, and polymers were grown from these sites to obtain particles with variable grafting densities and chain lengths that form SAMMs at an air–water interface. Even under conditions of low grafting density, these materials retain the ability to form SAMMs and their free-standing ability. Changes in particle arrangement within the monolayers were investigated using SEM imaging, and the toughness of the monolayers was evaluated using a film-on-water (FOW) method. Furthermore, coarse-grained molecular dynamics simulations were carried out to elucidate the morphology and mechanical properties of the monolayers. Findings from both experiments and simulations indicate that the toughness of SAMMs is more heavily influenced by the chain length of the grafted polymers than by the overall polymer content in the composite.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗