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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

The nano- and meso-scale structure of amorphous calcium carbonate

Abstract Understanding the underlying processes of biomineralization is crucial to a range of disciplines allowing us to quantify the effects of climate change on marine organisms, decipher the details of paleoclimate records and advance the development of biomimetic materials. Many biological minerals form via intermediate amorphous phases, which are hard to characterize due to their transient nature and a lack of long-range order. Here, using Monte Carlo simulations constrained by X-ray and neutron scattering data together with model building, we demonstrate a method for determining the structure of these intermediates with a study of amorphous calcium carbonate (ACC) which is a precursor in the bio-formation of crystalline calcium carbonates. We find that ACC consists of highly ordered anhydrous nano-domains of approx. 2 nm that can be described as nanocrystalline. These nano-domains are held together by an interstitial net-like matrix of water molecules which generate, on the mesoscale, a heterogeneous and gel-like structure of ACC. We probed the structural stability and dynamics of our model on the nanosecond timescale by molecular dynamics simulations. These simulations revealed a gel-like and glassy nature of ACC due to the water molecules and carbonate ions in the interstitial matrix featuring pronounced orientational and translational flexibility. This allows for viscous mobility with diffusion constants four to five orders of magnitude lower than those observed in solutions. Small and ultra-small angle neutron scattering indicates a hierarchically-ordered organization of ACC across length scales that allow us, based on our nano-domain model, to build a comprehensive picture of ACC formation by cluster assembly from solution. This contribution provides a new atomic-scale understanding of ACC and provides a framework for the general exploration of biomineralization and biomimetic processes.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Mobile barrier mechanisms for Na + -coupled symport in an MFS sugar transporter

While many 3D structures of cation-coupled transporters have been determined, the mechanistic details governing the obligatory coupling and functional regulations still remain elusive. The bacterial melibiose transporter (MelB) is a prototype of major facilitator superfamily transporters. With a conformation-selective nanobody, we determined a low-sugar affinity inward-facing Na + -bound cryoEM structure. The available outward-facing sugar-bound structures showed that the N- and C-terminal residues of the inner barrier contribute to the sugar selectivity. The inward-open conformation shows that the sugar selectivity pocket is also broken when the inner barrier is broken. Isothermal titration calorimetry measurements revealed that this inward-facing conformation trapped by this nanobody exhibited a greatly decreased sugar-binding affinity, suggesting the mechanisms for substrate intracellular release and accumulation. While the inner/outer barrier shift directly regulates the sugar-binding affinity, it has little or no effect on the cation binding, which is supported by molecular dynamics simulations. Furthermore, the hydron/deuterium exchange mass spectrometry analyses allowed us to identify dynamic regions; some regions are involved in the functionally important inner barrier-specific salt-bridge network, which indicates their critical roles in the barrier switching mechanisms for transport. These complementary results provided structural and dynamic insights into the mobile barrier mechanism for cation-coupled symport.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Using Molecular Structure to Tune Intrachain and Interchain Charge Transport in Indacenodithiophene-Based Copolymers

Here, in this work, we compare two structurally near-amorphous rigid-rod polymers-poly(indacenodithiophene-co-benzothiadiazole), p(IDT-BT), and poly(indacenodithiophene-co-benzopyrollodione), p(IDT-BPD)-with orders of magnitude different mobilities to understand the effect charge carrier intrachain delocalization has on electronic transport. Quantum chemical calculations show that p(IDT-BPD) has a barrier to torsion that is significantly lower than that of p(IDT-BT) and is thus more likely to have reduced conjugation lengths. We utilize absorption and photoluminescence spectroscopy to characterize energetic disorder and show that p(IDT-BPD) has higher energetic disorder. Charge modulation spectroscopy (CMS) and model calculations are used to show that charge carriers are substantially delocalized in p(IDT-BT) and occupy near-uniform energetic environments. We find that mobility activated hopping barriers are similar in these two materials. Electronic structure calculations show that both intrachain and interchain couplings of monomer units are poor enough in p(IDT-BPD) that charge carriers collapse to single IDT units and transport via a through-space tunneling mechanism. This work highlights the remarkable charge transport properties of p(IDT-BT) by showing that high mobilities are achievable on device-relevant length scales with only 1D carrier delocalization.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Nanoconfinement of Carbon Dioxide within Interfacial Aqueous/Ionic Liquid Systems

Nanoporous, gas-selective membranes have shown encouraging results for the removal of CO 2 from flue gas, yet the optimal design for such membranes is often unknown. Therefore, we used molecular dynamics simulations to elucidate the behavior of CO 2 within aqueous and ionic liquid (IL) systems ([EMIM][TFSI] and [OMIM][TFSI]), both confined individually and as an interfacial aqueous/IL system. We found that within aqueous systems the mobility of CO 2 is reduced due to interactions between the CO 2 oxygens and hydroxyl groups on the pore surface. Within the IL systems, we found that confinement has a greater effect on the [EMIM][TFSI] system as opposed to the [OMIM][TFSI] system. Paradoxically, the larger and more asymmetrical [OMIM]+ molecule undergoes less efficient packing, resulting in fewer confinement effects. Finally, free energy surfaces of the nanoconfined aqueous/IL interface demonstrate that CO 2 will transfer spontaneously from the aqueous to the IL phase.

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

Working principles of doping-well structures for high-mobility two-dimensional electron systems

Suppressing electron scattering is essential to achieve high-mobility two-dimensional electron systems (2DESs) that are clean enough to probe exotic interaction-driven phenomena. In heterostructures it is common practice to utilize modulation doping, where the ionized dopants are physically separated from the 2DES channel. The doping-well structure augments modulation doping by providing additional screening for all types of charged impurities in the vicinity of the 2DES, which is necessary to achieve record-breaking samples. Despite its prevalence in the design of ultrahigh-mobility 2DESs, the working principles of the doping-well structure have not been reported. As such, here we elaborate on the mechanics of electron transfer from doping wells to the 2DES, focusing on GaAs/AlGaAs samples grown by molecular beam epitaxy. Based on this understanding we demonstrate how structural parameters in the doping well can be varied to tune the properties of the 2DES.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Lithium Solvation and Mobility in Ionic Liquid Electrolytes with Asymmetric Sulfonyl-Cyano Anion

The solvation structure and transport properties of Li + in ionic liquid (IL) electrolytes based on n-methyl-n-butylpyrrolidinium cyano(trifluoromethanesulfonyl)imide [PYR 14 ][CTFSI] and [Li][CTFSI] (0 ≤ x Li ≤ 0.7) were studied by Raman and Nuclear Magnetic Resonance (NMR) diffusometry, and molecular dynamics (MD) simulations. At x Li < 0.3, Li + coordination is dominated by the cyano group. As x Li is increased, free cyano-sites become limited, resulting in increased coordination via the sulfonyl group. Here, the 1:1 mixture of the symmetric anions bis(trifluoromethanesulfonyl)imide ([TFSI]) and dicyanamide ([DCA]) results in similar physical properties as the IL with [CTFSI]. However, anion asymmetry is shown to increase Li-salt solubility and promote Li+ transference. The lifetimes of Li + -cyano coordination for [CTFSI] are calculated to be shorter than those for [DCA], indicating that the competition from the sulfonyl group weakens its solvation with Li + . This resulted in higher Li + transference for the electrolyte with [CTFSI]. In relation to the utility of these electrolytes in energy storage, the Li–LiFePO 4 half cells assembled with IL electrolyte (x Li = 0.3, 0.5, and 0.7) demonstrated a nominal capacity of 140 mAh/g at 0.1C rate and 90 °C where the cell with x Li = 0.7 IL electrolyte demonstrated 61% capacity retention after 100 cycles and superior rate capability owing to increased electrochemical stability.

25 ENERGY STORAGE↗
DOE OSTI2022

Understanding the Impacts of Support–Polymer Interactions on the Dynamics of Poly(ethyleneimine) Confined in Mesoporous SBA-15

Supported amines are a promising class of CO 2 sorbents offering large uptake capacities and fast uptake rates. Additionally, among supported amines, poly(ethyleneimine) (PEI) physically impregnated in the mesopores of SBA-15 silica is widely used. Within these composite materials, the chain dynamics and morphologies of PEI strongly influence the CO 2 capture performance, yet little is known about chain and macromolecule mobility in confined pores. Here, we probe the impact of the support–PEI interactions on the dynamics and structures of PEI at the support interface and the corresponding impact on CO 2 uptake performance, which yields critical structure–property relationships. The pore walls of the support are grafted with organosilanes with different chemical end groups to differentiate interaction modes (spanning from strong attraction to repulsion) between the pore surface and PEI. Combinations of techniques, such as quasi-elastic neutron scattering (QENS), 1 H T 1 –T 2 relaxation correlation solid-state NMR, and molecular dynamics (MD) simulations, are used to comprehensively assess the physical properties of confined PEI. We hypothesized that PEI would have faster dynamics when subjected to less attractive or repulsive interactions. However, we discover that complex interfacial interactions resulted in complex structure–property relationships. Indeed, both the chain conformation of the surface-grafted chains and of the PEI around the surface influenced the chain mobility and CO 2 uptake performance. By coupling knowledge of the dynamics and distributions of PEI with CO 2 sorption performance and other characteristics, we determine that the macroscopic structures of the hybrid materials dictate the first rapid CO 2 uptake, and the rate of CO 2 sorption during the subsequent gradual uptake stage is determined by PEI chain motions that promote diffusive jumps of CO 2 through PEI-packed domains.

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

Two-step annealing induced structural rejuvenation: A cause for memory effect in metallic glasses

The structural origin of the memory effect is still elusive in glassy materials. Here, in this letter, the memory effect in a series of metallic glasses (MGs) is observed by two step annealing using differential scanning calorimetry (DSC) and molecular dynamics simulations. It demonstrates that the Kovacs peak can be reflected from not only the system potential energy but also the atomic dynamics, showing the memory effect could originate from the formation of more loose packing configurations around mobile atoms by structural rejuvenation in the second step of high temperature annealing. In contrast, the high-low temperature annealing protocol can only induce the monotonic relaxation. Therefore, our results pave a pathway to better understand the origin of memory effect in MGs and other glassy materials from their dynamics and local atomic structure.

Memory effect↗
DOE OSTI2025

Preprocessing Affords 3D Crystalline Poly(3-hexylthiophene) Structure

The aggregation and crystallization of poly(3-hexylthiophene- 2,5-diyl) (P3HT), a representative active layer material used for organic field-effect transistor (OFET) applications, are influenced by the solution pretreatment and deposition process. This study explores vibration-assisted convective deposition for the fabrication of OFETs in comparison to spin coating, blade coating, and convective deposition without vibration. The ultraviolet–visible spectroscopic analysis demonstrates that convective deposition, especially assisted with vibration, leads to a greater degree of intrachain interactions, longer conjugation length, and enhanced polymer backbone planarization. When the P3HT solution is preprocessed via sonication and aging, the P3HT films exhibit J-like aggregation, and (h11) peaks can be observed through grazing-incidence wide-angle X-ray scattering, suggesting an ordered 3D crystalline structure. OFETs based on such films exhibit high mobilities (up to 0.14 cm 2 V –1 s –1 ). The results point to the sensitivity of P3HT charge transport behavior to the intramolecular interactions and backbone planarity and further deepen our understanding of the relationship between processing, aggregates, molecular ordering, and resultant device properties.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Optical properties of cubic boron arsenide

The ultrahigh thermal conductivity of cubic boron arsenide (BAs) makes it a promising material for next-generation electronics and optoelectronics. Here, we report measured optical properties of BAs crystals, including the complex dielectric function, refractive index, and absorption coefficient in the ultraviolet, visible, and near-infrared wavelength range. In this work, the data were collected at room temperature using spectroscopic ellipsometry and transmission and reflection spectroscopy. We further calculated the optical response using density functional theory and many-body perturbation theory, considering quasiparticle and excitonic corrections. The computed values for the direct and indirect bandgaps (4.25 eV and 2.07 eV) agree well with the measured results (4.12 eV and 2.02 eV). Our findings pave the way for using BAs in future electronic and optoelectronic applications that take advantage of its demonstrated ultrahigh thermal conductivity and predicted high ambipolar carrier mobility.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2025

Role of Polymer Architecture in CO 2 Capture from Air Using Supported Poly(alkylenimine)s: Linear vs Branched Polymers

Direct air capture (DAC) of CO 2 coupled with geologic storage is a promising climate change mitigation strategy, with some applications employing amines supported on porous solids as CO 2 sorbents. While branched poly(ethylenimine) (PEI) is the standard benchmark amine material, it suffers from limited oxidative stability. Poly(propylenimine) (PPI), as an alternative, has previously demonstrated improved resistance to degradation under harsh oxidative conditions. Linear and branched PEI are commercially available, though at different molecular weights, while PPI is not commercially available. For this reason, a comparative study of all four polymers (linear PEI, branched PEI, linear PPI, branched PPI) has not been reported for DAC. In this study, we synthesize and compare low-molecular-weight (∼800 g/mol) linear (L) and branched (B) PEI and PPI supported on a model support, SBA-15 silica. These materials are evaluated for CO 2 adsorption under dry, DAC-relevant conditions (400 ppm of CO 2 , 30 °C). LPPI exhibited the highest amine efficiency at all loadings, reaching a maximum of 0.14 mmol CO 2 /mmol N, outperforming BPEI, while LPEI consistently showed the lowest uptake capacity. Temperature-programmed desorption reveals that the structure of the amine polymer impacts the CO 2 binding strength, with branched polymers displaying higher desorption energies of 102−111 kJ/mol. In situ infrared spectroscopy experiments show that all sorbents preferentially capture CO 2 as ammonium carbamate. Isobaric CO 2 uptake studies further underscore the influence of polymer mobility and support pore crowding on performance, while demonstrating the sorbents’ performance at elevated temperatures and CO 2 concentrations. All materials demonstrated good stability over 25 adsorption−desorption cycles using thermal regeneration in an inert gas purge, with only BPPI displaying a 10−11% decrease in capacity/amine efficiency during cycling, possibly due to the loss of low molecular weight, oligomeric amines. This is the first side-by-side comparison of the CO 2 sorption properties of linear and branched PEI and PPI with similar molecular weights. These findings highlight the significant role of polymer architecture in CO 2 capture efficiency and inform future designs of durable, high-performance DAC sorbents.

adsorbents↗
DOE OSTI2020

Dislocation dynamics in polycrystalline materials

An extension of the dislocation dynamics method to polycrystalline materials is presented with emphasis on handling interactions between dislocations and grain boundaries. The key new features of the method include: (1) a grain boundary detection algorithm, (2) new dislocation emission criteria based on power dissipation and area growth, (3) mobility of dislocations at grain boundaries, and (4) extension of topological operations e.g. mesh adaption, collision, and dissociation to handle dislocations interacting with grain boundaries. Furthermore, verification and validation examples are executed to compare our calculations with existing analytic methods, molecular dynamics simulations, and experimental observations.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Investigation of Molecular Diffusion at Block Copolymer Thin Films Using Maximum Entropy Method-Based Fluorescence Correlation Spectroscopy and Single Molecule Tracking

Fluorescence correlation spectroscopy (FCS) has been widely used to investigate molecular diffusion behavior in various samples. The use of the maximum entropy method (MEM) for FCS data analysis provides a unique means to determine multiple distinct diffusion coefficients without a priori assumption of their number. Comparison of the MEM-based FCS method (MEM-FCS) with another method will reveal its utility and advantage as an analytical tool to investigate diffusion dynamics. Herein, we measured diffusion of fluorescent probes doped into nanostructured thin films using MEM-FCS, and validated the results with single molecule tracking (SMT) data. The efficacy of the MEM code employed was first demonstrated by analyzing simulated FCS data for systems incorporating one and two diffusion modes with broadly distributed diffusion coefficients. The MEM analysis accurately afforded the number of distinct diffusion modes and their mean diffusion coefficients. These results contrasted with those obtained by fitting the simulated data to conventional two-component and anomalous diffusion models, which yielded inaccurate estimates of the diffusion coefficients. Subsequently, the MEM analysis was applied to FCS data acquired from hydrophilic dye molecules incorporated into microphase-separated polystyrene-block-poly(ethylene oxide) (PS-b-PEO) thin films characterized under a water-saturated nitrogen atmosphere. The MEM analysis revealed distinct fast and slow diffusion components attributable to molecules diffusing on the film surface and inside the film, respectively. SMT studies of the same materials yielded trajectories for mobile molecules that appear to follow the curved PEO microdomains. Diffusion coefficients obtained from the SMT data were consistent with those obtained for the slow diffusion component detected by MEM-FCS. Furthermore, these results highlight the utility of MEM-FCS and SMT for gaining complementary information on molecular diffusion processes in heterogeneous material systems.

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

Computational tools and algorithms for ion mobility spectrometry-mass spectrometry

Ion mobility spectrometry-mass spectrometry (IMS-MS or IM-MS) is a powerful analytical technique that combines the gas-phase separation capabilities of IM with the identification and quantification capabilities of MS. IM-MS can differentiate molecules with indistinguishable masses but different structures (e.g., isomers, isobars, molecular classes, and contaminant ions). The importance of this analytical technique is reflected by a staged increase in the number of applications for molecular characterization across a variety of fields, from different MS-based omics (proteomics, metabolomics, lipidomics, etc.) to the structural characterization of glycans, organic matter, proteins, and macromolecular complexes. With the increasing application of IM-MS there is a pressing need for effective and accessible computational tools. This article presents an overview of the most recent free and open-source software tools specifically tailored for the analysis and interpretation of data derived from IM-MS instrumentation. This review enumerates these tools and outlines their main algorithmic approaches, while highlighting representative applications across different fields. Finally, a discussion of current limitations and expectable improvements is presented.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Charge Transport in Twisted Organic Semiconductor Crystals of Modulated Pitch

Many molecular crystals (approximately one third) grow as twisted, helicoidal ribbons from the melt, and this preponderance is even higher in restricted classes of materials, for instance, charge-transfer complexes. Previously, twisted crystallites of such complexes present an increase in carrier mobilities. In this paper, the effect of twisting on charge mobility is better analyzed for a monocomponent organic semiconductor, 2,5-bis(3-dodecyl-2-thienyl)-thiazolo[5,4-d]thiazole (BDT), that forms twisted crystals with varied helicoidal pitches and makes possible a correlation of twist strength with carrier mobility. Films are analyzed by X-ray scattering and Mueller matrix polarimetry to characterize the microscale organization of the polycrystalline ensembles. Carrier mobilities of organic field-effect transistors are five times higher when the crystals are grown with the smallest pitches (most twisted), compared to those with the largest pitches, along the fiber elongation direction. A tenfold increase is observed along the perpendicular direction. Simulation of electrical potential based on scanning electron microscopy images and density functional theory suggests that the twisting-enhanced mobility is mainly controlled by the fiber organization in the film. A greater number of tightly packed twisted fibers separated by numerous smaller gaps permit better charge transport over the film surface compared to fewer big crystallites separated by larger gaps.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Naphthalene‐Diimide‐Based Ionenes as Universal Interlayers for Efficient Organic Solar Cells

Abstract Self‐doping ionene polymers were efficiently synthesized by reacting functional naphthalene diimide (NDI) with 1,3‐dibromopropane ( NDI‐NI ) or trans ‐1,4‐dibromo‐2‐butene ( NDI‐CI ) via quaternization polymerization. These NDI‐based ionene polymers are universal interlayers with random molecular orientation, boosting the efficiencies of fullerene‐based, non‐fullerene‐based, and ternary organic solar cells (OSCs) over a wide range of interlayer thicknesses, with a maximum efficiency of 16.9 %. NDI‐NI showed a higher interfacial dipole (Δ), conductivity, and electron mobility than NDI‐CI , affording solar cells with higher efficiencies. These polymers proved to efficiently lower the work function ( WF ) of air‐stable metals and optimize the contact between metal electrode and organic semiconductor, highlighting their power to overcome energy barriers of electron injection and extraction processes for efficient organic electronics.

Liu, Ming↗
DOE OSTI2020

Naphthalene‐Diimide‐Based Ionenes as Universal Interlayers for Efficient Organic Solar Cells

Abstract Self‐doping ionene polymers were efficiently synthesized by reacting functional naphthalene diimide (NDI) with 1,3‐dibromopropane ( NDI‐NI ) or trans ‐1,4‐dibromo‐2‐butene ( NDI‐CI ) via quaternization polymerization. These NDI‐based ionene polymers are universal interlayers with random molecular orientation, boosting the efficiencies of fullerene‐based, non‐fullerene‐based, and ternary organic solar cells (OSCs) over a wide range of interlayer thicknesses, with a maximum efficiency of 16.9 %. NDI‐NI showed a higher interfacial dipole (Δ), conductivity, and electron mobility than NDI‐CI , affording solar cells with higher efficiencies. These polymers proved to efficiently lower the work function ( WF ) of air‐stable metals and optimize the contact between metal electrode and organic semiconductor, highlighting their power to overcome energy barriers of electron injection and extraction processes for efficient organic electronics.

Liu, Ming↗