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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Lithium crystallization at solid interfaces

Understanding the electrochemical deposition of metal anodes is critical for high-energy rechargeable batteries, among which solid-state lithium metal batteries have attracted extensive interest. A long-standing open question is how electrochemically deposited lithium-ions at the interfaces with the solid-electrolytes crystalize into lithium metal. Here, using large-scale molecular dynamics simulations, we study and reveal the atomistic pathways and energy barriers of lithium crystallization at the solid interfaces. In contrast to the conventional understanding, lithium crystallization takes multi-step pathways mediated by interfacial lithium atoms with disordered and random-closed-packed configurations as intermediate steps, which give rise to the energy barrier of crystallization. This understanding of multi-step crystallization pathways extends the applicability of Ostwald’s step rule to interfacial atom states, and enables a rational strategy for lower-barrier crystallization by promoting favorable interfacial atom states as intermediate steps through interfacial engineering. Our findings open rationally guided avenues of interfacial engineering for facilitating the crystallization in metal electrodes for solid-state batteries and can be generally applicable for fast crystal growth.

25 ENERGY STORAGE↗
NASA NTRS1979

Determination of physical and chemical states of lubricants in concentrated contacts, part 1

A Fourier emission infrared microspectrometer, set up on a vibration-proof optical table and interfaced to a dedicated minicomputer, was used to record infrared emission spectra from elastohydrodynamic bearing contacts. Its range was extended to cover the entire mid-infrared from 2 to 15 micron. A series of experiments with 5P4E polyphenyl ether showed the existence of a temperature gradient through the lubricant in an ehd contact, which is perpendicular to the flow direction. The experiments also show marked polarization of some of the spectral bands, indicating a molecular alignment. Alignment is less evident at high pressure than at low pressure. To account for this behavior, a model is suggested along the lines developed for the conformational changes observed in long-chain polymers when subjected to increased pressure--to accommodate closer packing, molecules become kinked and curl up. Experiments with a traction fluid showed periodic changes of flow pattern associated with certain spectral changes. These observations will be studied further. A study by infrared attenuated total reflection spectrophotometry was undertaken to determine whether gamma irradiation would change polyethylene wear specimens. The results were negative.

Lauer, J. L.↗
DOE OSTI2025

Multistage nucleation pathway in LiF molten salt mirrors the crystal–melt interface structure

Despite over a century of studies, fundamental questions remain about the processes governing crystal nucleation from melts or solutions. Research over the past three decades has presented mounting evidence for kinetic pathways of crystal nucleation that are more complex than envisioned by the simplest forms of classical theory. Such observations have been presented for colloidal and elemental systems with covalent and metallic bonding. Despite the technological and geochemical importance of molten salts, similar studies for these ionically bonded systems are currently lacking. Here we develop a machine learning interatomic potential for a model ionic system: LiF. The potential features quantum-level accuracy for both liquid and multiple solid polymorphs over wide temperature and pressure ranges and accurately reproduces experimentally measured properties. Thanks to the efficiency of the potential, which enables microsecond-scale molecular dynamics simulations, induction times for nucleation of LiF solids from their melts are computed over a range of undercoolings. With the aid of a set of robust local order parameters established here, the simulations reveal that homogeneous crystal nucleation in undercooled melts preferentially initiates from liquid regions showing slow dynamics and high bond orientational order simultaneously, and the second-shell order of both precritical nuclei and the surface of postcritical nuclei is dominated by hexagonal close packing and body-centered cubic local structure, even though the nucleus core is dominated by face-centered cubic structure corresponding to the stable rocksalt crystal structure. Finally, we establish a connection between the crystallization pathway and the equilibrium crystal-melt interface structure.

Applied Physical Sciences↗
DOE OSTI2021

Kinetics of Direct Olefin Synthesis from Syngas over Mixed Beds of Zn–Zr Oxides and SAPO-34

A packed bed containing a physical mixture of both Zn–Zr mixed oxide catalyst and SAPO-34 converts syngas directly into a mixture of C 2 –C 5 olefins and paraffins. Specifically, the mixed oxide catalyst is responsible for intermediate oxygenate synthesis from syngas while the molecular sieve catalyzes olefin synthesis from the oxygenate intermediates. Kinetic measurements with cofed propylene over each catalyst independently confirm olefin hydrogenation activity over both components of the composite bed. The addition of either water or CO to the feed drops the activity of propylene hydrogenation over the Zn–Zr oxide. In sum, under reaction conditions of syngas feed and produced water, olefin hydrogenation predominantly occurs over the SAPO-34 catalyst, rather than over the catalyst responsible for hydrogenating CO into oxygenate intermediates. Here, a developed kinetic model consistent with this conclusion describes measurements at differing feed compositions, temperatures, space velocities, and bed catalyst mixing ratios. Technoeconomic analysis of the process indicates that the olefin-to-paraffin ratio is a key performance metric for commercial scale syngas conversion and highlights the importance of considering olefin hydrogenation rates over the molecular sieve component.

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

Enriched Molecular-Level View of Saline Wetland Soil Carbon by Sensitivity-Enhanced Solid-State NMR

Soil organic matter (SOM) plays a major role in mitigating greenhouse gas emission and regulating earth’s climate, carbon cycle, and biodiversity. Wetland soils account for one-third of all SOM; however, globally, coastal wetland soils are eroding faster due to increasing sea-level rise. Our understanding of carbon sequestration dynamics in wetlands lags behind that of upland soils. Here, we employ solid-state nuclear magnetic resonance (ssNMR) to investigate the molecular-level structure of biopolymers in wetland soils spanning 11 centuries. High-resolution multidimensional spectra, enabled by dynamic nuclear polarization (DNP), demonstrate enduring preservation of molecular structures within herbaceous plant cores, notably condensing aromatic motifs and carbohydrates, even over a millennium, with the preserved cores constituting a decreasing minority among molecules from decomposition and repolymerization with depth and age. Such preserved cores occur alongside molecules from the decomposition of loosely packed parent biopolymers. These findings emphasize the relative vulnerability of coastal wetland SOM when exposed to oxygenated water due to geological and anthropogenic changes.

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

Patchy nanoparticles by atomic stencilling

Stencilling, in which patterns are created by painting over masks, has ubiquitous applications in art, architecture and manufacturing. Modern, top-down microfabrication methods have succeeded in reducing mask sizes to under 10 nm, enabling ever smaller microdevices as today’s fastest computer chips. Meanwhile, bottom-up masking using chemical bonds or physical interactions has remained largely unexplored, despite its advantages of low cost, solution-processability, scalability and high compatibility with complex, curved and three-dimensional (3D) surfaces. Here we report atomic stencilling to make patchy nanoparticles (NPs), using surface-adsorbed iodide submonolayers to create the mask and ligand-mediated grafted polymers onto unmasked regions as ‘paint’. We use this approach to synthesize more than 20 different types of NP coated with polymer patches in high yield. Polymer scaling theory and molecular dynamics (MD) simulation show that stencilling, along with the interplay of enthalpic and entropic effects of polymers, generates patchy particle morphologies not reported previously. These polymer-patched NPs self-assemble into extended crystals owing to highly uniform patches, including different non-closely packed superlattices. We propose that atomic stencilling opens new avenues in patterning NPs and other substrates at the nanometre length scale, leading to precise control of their chemistry, reactivity and interactions for a wide range of applications, such as targeted delivery, catalysis, microelectronics, integrated metamaterials and tissue engineering.

36 MATERIALS SCIENCE↗
NASA NTRS2003

Towards the Structure Determination of a Modulated Protein Crystal: The Semicrystalline State of Profilin:Actin

One of the remaining challenges to structural biology is the solution of modulated structures. While small molecule crystallographers have championed this type of structure, to date, no modulated macromolecular structures have been determined. Modulation of the molecular structures within the crystal can produce satellite reflections or a superlattice of reflections in reciprocal space. We have developed the data collection methods and strategies that are needed to collect and analyze these data. If the macromolecule's crystal lattice is composed of physiologically relevant packing contacts, structural changes induced under physiological conditions can cause distortion relevant to the function and biophysical processes of the molecule making up the crystal. By careful measurement of the distortion, and the corresponding three-dimensional structure of the distorted molecule, we will visualize the motion and mechanism of the biological macromolecule(s). We have measured the modulated diffraction pattern produced by the semicrystalline state of profilin:actin crystals using highly parallel and highly monochromatic synchrotron radiation coupled with fine phi slicing (0.001-0.010 degrees) for structure determination. These crystals present these crystals present a unique opportunity to address an important question in structural biology. The modulation is believed to be due to the formation of actin helical filaments from the actin beta ribbon upon the pH-induced dissociation of profilin. To date, the filamentous state of actin has resisted crystallization and no detailed structures are available. The semicrystalline state profilin:actin crystals provides a unique opportunity to understand the many conformational states of actin. This knowledge is essential for understanding the dynamics underlying shape changes and motility of eukaryotic cells. Many essential processes, such as cytokinesis, phagocytosis, and cellular migration depend upon the capacity of the actin microfilament system to be restructured in a controlled manner via polymerization, depolymerization, severing, cross-linking, and anchorage. The structure the semicrystalline state of profilin:actin will challenge and validate current models of muscle contraction and cell motility. The methodology and theory under development will be easily extendable to other systems.

Borgstahl, G.↗
DOE OSTI2024

Speciation and Organic Phase Structure in Nitric Acid Extraction with Trioctylamine

Understanding chemical speciation and intermolecular interactions in multicomponent liquids is essential to understanding their phase and chemical equilibria, which underpin chemical separation processes, including solvent extraction. Here we report on the extraction of nitric acid from its aqueous solutions into organic solutions of trioctylamine (TOA) in toluene, investigated with spectroscopic, X-ray scattering, and computational tools to understand molecular speciation in the organic phase and its relationship with the nanoscale structure of the organic phase. Trends in acid and water extraction clearly show two and three regimes, respectively, indicating different stoichiometric relationships, but speciation of HNO 3 , water, and amine in these regimes is not apparent. 1 H NMR of the organic phase shows that there are at least two distinct acidic protons in the organic phase while ATR-FTIR results show that the organic phase with excess acid extraction is a mixture of trioctylammonium-nitrate ion pairs (TOAHNO 3 ), and undissociated HNO 3 molecules. Comparison with DFT-computed IR spectra show that the chain-like configurations of TOAHNO 3 HNO 3 H 2 O are favored over TOAHNO 3 H 2 OHNO 3 , i.e., direct interaction between the nitrate and HNO 3 molecules is more favored compared to a water-mediated interaction. SAXS of the organic phases were modeled as sums of Ornstein-Zernike (O-Z) scattering and a prepeak feature in the higher Q region that corresponds to extractant packing. The extraction of undissociated HNO 3 by the ion pairs leads to an increased X-ray scattering contrast in the organic phase without any significant change in the correlation length. These results show that the organic phase nanostructure is more sensitive to the concentration of TOAHNO 3 and is relatively unaffected by excess acid extraction. Finally, these findings will enable a molecular understanding of the mechanisms behind metal extraction from acidic media with basic extractants.

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

Printing 2D Conjugated Polymer Monolayers and Their Distinct Electronic Properties

Abstract Recently, 2D monolayer films of conjugated polymers have gained increasing attention owing to the preeminence of 2D inorganic films that exhibit unique optoelectronic and mechanical properties compared to their bulk analogs. Despite numerous efforts, crystallization of semiconducting polymers into highly ordered 2D monolayer films still remains challenging. Herein, a dynamic‐template‐assisted meniscus‐guided coating is utilized to fabricate continuous, highly ordered 2D monolayer films of conjugated polymers over a centimeter scale with enhanced backbone π–π stacking. In contrast, monolayer films printed on solid substrates confer upon the 1D fiber networks strong alkyl side‐chain stacking at the expense of backbone packing. From single‐layers to multilayers, the polymer π‐stacks change from edge‐on to bimodal orientation as the film thickness reaches ≈20 nm. Spectroscopic and cyclic voltammetry analysis reveals an abrupt increase in J‐aggregation and absorption coefficient and a decrease in bandgap and highest occupied molecular orbital level until critical thickness, possibly arising from the straightened polymer backbone. This is corroborated by an abrupt increase in hole mobility with film thickness, reaching a maximum of 0.7 cm 2 V −1 s −1 near the critical thickness. Finally, fabrication of chemical sensors incorporating polymer films of various thicknesses is demonstrated, and an ultrahigh sensitivity of the ≈7 nm thick ultrathin film (bilayers) to 1 ppb ammonia is shown.

Kafle, Prapti↗
NASA NTRS2018

Characterization of Sorbents for Controlling Ammonia in Spacecraft Cabin Air

The trace contaminant control system (TCCS) utilizes packed beds of Barnebey-Sutcliffe (B-S) Type 3032 to remove ammonia from ISS (International Space Station) cabin air. BS Type 3032, an acid-impregnated activated carbon, is no longer produced and must be replaced. The adsorptive capacities of Calgon Carbon Ammonasorb II and Molecular Products Chemsorb® 1425 for ammonia were measured using moist (40% RH (Relative Humidity)) spacecraft simulated gas streams. These candidate replacement sorbents had 66% greater ammonia removal capacities at low (5 ppm) ammonia concentrations than B-S Type 3032.

Monje, Oscar↗
DOE OSTI2021

Anomalous fast atomic dynamics in bulk metallic glasses

It is believed that the strong glass formers tend to be dense packing and have rather slow atomic dynamics. Here, we report that the anomalous fast atomic dynamics exist in an Au 55 Cu 20 Ag 5 Si 20 metallic glass (MG) with good glass forming ability (GFA) by combining X-ray photon correlation spectroscopy measurements with ab initio molecular dynamics simulations. The fast dynamics are mainly originated from the increased mobility of Cu atoms by Ag addition. Ag atoms are inclined to locate at Cu-centered <0, 2, 8, 1> motifs, which slow or accelerate the dynamics of shell Cu atoms, depending on whether Ag atoms appear at the first shells or not, leading to the formation of structural heterogeneity at the atomic level. The results enrich the understanding of atomic dynamics in Cue-Ag-containing MGs and will trigger more studies on the dynamics-GFA relationship in MGs.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2022

Evidence that gecko setae are coated with an ordered nanometre-thin lipid film

The fascinating adhesion of gecko to virtually any material has been related to surface interactions of myriads of spatula at the tips of gecko feet. Surprisingly, the molecular details of the surface chemistry of gecko adhesion are still largely unknown. Lipids have been identified within gecko adhesive pads. However, the location of the lipids, the extent to which spatula are coated with lipids, and how the lipids are structured are still open questions. Lipids can modulate adhesion properties and surface hydrophobicity and may play an important role in adhesion. We have therefore studied the molecular structure of lipids at spatula surfaces using near-edge X-ray absorption fine structure imaging. We provide evidence that a nanometre-thin layer of lipids is present at the spatula surfaces of the tokay gecko (Gekko gecko) and that the lipids form ordered, densely packed layers. Such dense, thin lipid layers can effectively protect the spatula proteins from dehydration by forming a barrier against water evaporation. Lipids can also render surfaces hydrophobic and thereby support the gecko adhesive system by enhancement of hydrophobic–hydrophobic interactions with surfaces.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Cryo-EM structure of the diapause chaperone artemin

The protein artemin acts as both an RNA and protein chaperone and constitutes over 10% of all protein in Artemia cysts during diapause. However, its mechanistic details remain elusive since no high-resolution structure of artemin exists. Here we report the full-length structure of artemin at 2.04 Å resolution. The cryo-EM map contains density for an intramolecular disulfide bond between Cys22-Cys61 and resolves the entire C-terminus extending into the core of the assembled protein cage but in a different configuration than previously hypothesized with molecular modeling. We also provide data supporting the role of C-terminal helix F towards stabilizing the dimer form that is believed to be important for its chaperoning activity. We were able to destabilize this effect by placing a tag at the C-terminus to fully pack the internal cavity and cause limited steric hindrance.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Molecular Simulations of the Chain Length Dependent Adsorption of C7‐C14 n ‐Alkanes in ZIF‐8

Recent experiments show that the diffusivities of C8 and C10 n-alkanes in ZIF-8 are higher than those of C7 and C9, respectively. We investigated this unusual ‘odd-even' effect by simulating the adsorption of C7-C14 n-alkanes in ZIF-8 using hybrid Monte Carlo molecular simulations. The resultant adsorption isotherms, guest-host energies, isosteric heats, and chain length distributions are analyzed for trends among the n-alkanes. ZIF-8 cages filled with n-alkanes are characterized using a combination of image processing and data science to quantify the differences in packing that occur with chain length. In conclusion, results indicate that packing changes drastically from C7 to C8 and from C9 to C10, which is consistent with the diffusion trends previously reported in experiments.

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

Induced phase transformation in ionizable colloidal nanoparticles

Abstract Acid–base equilibria directly influence the functionality and behavior of particles in a system. Due to the ionizing effects of acid–base functional groups, particles will undergo charge exchange. The degree of ionization and their intermolecular and electrostatic interactions are controlled by varying the pH and salt concentration of the solution in a system. Although the pH can be tuned in experiments, it is hard to model this effect using simulations or theoretical approaches. This is due to the difficulty in treating charge regulation and capturing the cooperative effects in a colloidal suspension with Coulombic interaction. In this work, we analyze a suspension of ionizable colloidal particles via molecular dynamics (MD) simulations, along with Monte Carlo simulations for charge regulation (MC-CR) and derive a phase diagram of the system as a function of pH. It is observed that as pH increases, particles functionalized with acid groups change their arrangement from face-centered cubic (FCC) packing to a disordered state. We attribute these transitions to an increase in the degree of charge polydispersity arising from an increase in pH. Our work shows that charge regulation leads to amorphous solids in colloids when the mean nanoparticle charge is sufficiently high. Graphical abstract

36 MATERIALS SCIENCE↗
DOE OSTI2026

Atomistic Mechanisms of Stress-Dependent Molten Salt Corrosion in NiCr Alloys

Ni-based structural alloys in molten salt environments often experience simultaneous mechanical loading and corrosive attack, yet the mechanisms governing stress-corrosion interactions remain unclear. Prior studies largely emphasize tensile stress, while the role of compressive stress has received limited attention. Here, reactive molecular dynamics simulations are used to investigate the coupled effects of applied strain and corrosion in Ni 0.75 Cr 0.25 exposed to molten FLiNaK at 800 °C. A Σ5(210) grain boundary model is subjected to tensile (+4%) to compressive (−4%) uniaxial strains, and corrosion behavior is evaluated through fluorine adsorption, charge redistribution, and grain boundary evolution. Tensile strain accelerates intergranular corrosion susceptibility by reducing local atomic packing through elastic dilation and increasing excess free volume at the grain boundary, which enhances atomic mobility and salt infiltration. In contrast, compressive strain can suppress corrosion by promoting the formation of a ridge-like surface layer along the grain boundary, limiting salt access to the underlying alloy. These results provide atomistic insight into how stress states influence grain boundary corrosion in molten salts.

36 - MATERIALS SCIENCE↗
DOE OSTI2025

Harnessing nanoscale densification for controlling gas selectivity in flexible zeolitic imidazolate frameworks

Flexible metal-organic frameworks (MOFs) are promising for gas separation due to their molecular recognition capabilities. However, gate-opening behavior in certain flexible MOFs can reduce gas selectivity, enabling simultaneous adsorption of multiple gases. We introduce a binder-free, pressure-free densification process to enhance gas selectivity in flexible zeolitic imidazolate frameworks (ZIF-7 and ZIF-9) by optimizing nanoparticle packing. Unlike powders, the densified ZIF-7 and ZIF-9 retain rhombohedral crystal structures after solvent removal, confirmed via synchrotron powder X-ray diffraction. This process modifies adsorption behavior by introducing a diffusion barrier, enabling diffusivity-driven kinetic separation and enhanced CO2/hydrocarbon selectivity. At 0.5 bar, ZIF-7 mono shows 2×, 4×, and 9.5× higher CO 2 selectivity over C 2 H 2 , C 2 H 4 , and C 2 H 6 , respectively, versus ZIF-7 pwd . ZIF-9 mono similarly shows 6.5×, 3×, and 39× improvements over ZIF-9 pwd . Both monoliths outperform powders in ternary gas mixtures. This study provides a novel strategy to control gate opening and enhance gas selectivity in flexible MOFs for practical separation applications.

CO2/hydrocarbon separation↗
DOE OSTI2020

Confining Liquids inside Carbon Nanotubes: Accelerated Molecular Dynamics with Spliced, Soft-Core Potentials and Simulated Annealing

Understanding emergent phenomena of fluids under physical confinement requires the development of advanced tools for rapid and accurate simulation of their physiochemical properties. Simulating liquid molecules commensurate in size with the nanoscale enclosures that confine them is a key challenge. In this work, we demonstrate an accelerated molecular dynamics simulation technique that combines soft-core potentials (SCP) and simulated annealing (SA) to analyze confined liquids. This integrated SCP/SA method relies on a new spliced soft-core potential (SSCP), which enables tunable accuracy with respect to the target hard-core potential (HCP). SCP/SA enables the packing of enclosures with bulk material in a controlled, thermodynamically consistent manner. The enhanced SSCP accuracy is a critical feature of SCP/SA, enabling a smooth transition between the SCP and the HCP at a desired SCP hardness. We applied SCP/SA to the problem of filling a carbon nanotube (CNT) in periodic boundary conditions with a popular ionic liquid (IL), 1- butyl-3-methylimidazolium hexafluorophosphate $[\text{BMIM}^+][\text{PF}^–_6]$. We performed a series of triplicate simulations on systems with varying CNT diameter and charge to demonstrate SCP/SA’s versatility. Beyond this IL/CNT system, the SCP/SA simulation framework has a broad range of potential applications, not limited to nanoscale enclosures and interfaces, including both solid-state and biological systems.

36 MATERIALS SCIENCE↗