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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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116 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Solvent Processing and Ionic Liquid-Enabled Long-Range Vertical Ordering in Block Copolymer Films with Enhanced Film Stability

Rapid and reliable processing methods for forming ordered block copolymer (BCP) materials with low defect density in a thin film geometry are required for many nanotechnology applications. Vertically aligned BCP structures, in particular, have applications ranging from nanolithography for electronics and photonics to nanoporous membranes for water remediation and novel batteries for flexible electronics. However, the attainment of nearly complete vertical orientational order of the BCP ordered phase remains challenging. Solvent-based techniques, such as direct immersion annealing (DIA) and solvent vapor annealing (SVA), have immense potential for these applications of BCP films, as it allows for tuning of their thermodynamic, structural, and chain mobility driven kinetic properties. We first demonstrate that DIA, using a judicious choice of binary solvent mixtures along with a relatively hydrophobic ionic liquid (IL), induces the rapid vertical ordering in polystyrene-b-polymethylmethacrylate (PS-PMMA) block copolymer in lamellar films. The IL establishes synergy to the binary solvent mixture of toluene and heptane to 1 create a near-neutral solvent environment for attaining the vertical microstructure of the BCP. Next, we show that IL can suppress the de-wetting of the PS-PMMA films to achieve long-range order using SVA in cylindrical films for long annealing times. Both vertical and horizontal morphology is attained in these films by selecting different solvent environments. Furthermore, attaining enhanced vertical and horizontal BCP structure with long-range defect-free order by tuning solvent quality and using additives like IL can render them useful for many nanotech applications.

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NASA NTRS2002

Phase Transition in Dusty Plasmas: A Microphysical Description

Dust grains immersed in plasma discharges acquire a large negative charge and settle into a dust cloud at the edge of the sheath. In this region, the plasma ions stream toward the electrode at a velocity u approx. cs=(T(sub e)/m(sub i))(exp 1/2). Experimentally at sufficiently high gas pressure P, the random kinetic energy of the grains is damped by gas friction, and the grains are strongly coupled and self-organize into a crystalline configuration. For lower pressures despite the dissipation of grain kinetic energy to gas friction, the dust grains reach a steady-state kinetic temperature T(sub d) which is much larger than the temperature of any other component in the plasma. T(sub d) is so large that the dust acts like a fluid. We have used the dynamically shielded dust (DSD) model to simulate these physical processes. We find that the known experimental features are nicely reproduced in the simulations, and that additional features are revealed. In the figure we plot the variation of T(sub d) as P is continuously varied in a DSD code run. A marked difference is evident between the critical pressure P(sub m) for the melting transition as P is decreased, and the critical pressure P(sub c) for the condensation transition as P is increased. For P(sub m) is less than P is less than P(sub c), mixed phase states are seen. This hysteresis occurs because the instability which triggers melting is different from the instability that heats the dust in the fluid phase and inhibits freezing. At low pressure, the dust is subject to a two-stream instability with the ions. This instability is responsible for the high temperature of the dust at low pressure. The basic physics underlying the melting transition has been elucidated in a series of papers. We are developing a first-principles analytic approach to the melting transition, which embodies the same physics that is present in the DSD code.

Joyce, Glenn↗
DOE OSTI2023

Multi-modal chemical characterization of highly viscous submicrometer organic particles

Distinguishing highly viscous organic particles within complex mixtures of atmospheric aerosol and accurate descriptions of their composition, size distributions, and mixing states are challenges at the forefront of aerosol measurement science and technology. Here, we present results obtained from complementary single-particle measurement techniques employed for the in-depth characterization of highly viscous particles. In this study, we demonstrate advantages and synergy of this multi-modal particle characterization approach based on the analysis of individual viscous particles formed in the air-discharged waste produced by a common sewer pipe rehabilitation technology. Using oil immersion flow microscopy, we investigate particle size distributions and morphology of colloidal components present in field-collected aqueous waste condensates. We compare these results with corresponding measurements of viscous particles formed in drying droplets of the aerosolized discharged waste. The colloidal components and viscous particles were found to be approximately 10 µm and 0.5 µm, respectively. The aerosolized viscous particles exhibited a spherical morphology, while the colloidal particles appeared noticeably fractal, resembling fragments of a cured composite material. Chemical imaging of the viscous particles collected on substrates was performed using scanning electron microscopy and soft X-ray spectro-microscopy techniques. Through these methods, comprehensive description of these particles emerged, confirming their high solid-like viscosity, wide-ranging sizes, diverse carbon speciation with high degrees of oxygenation, and high organic volume fractions. The aerosolized viscous particles were further characterized using high-throughput single particle mass spectrometry. This technique provides real-time measurements of composition, size, and morphological metrics for large numbers of individual particles, enabling the identification of their distinct mass spectrometric signatures.

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DOE OSTI2022

First Principles Determination of the Potential-of-Zero-Charge in an Alumina-Coated Aluminum/Water Interface Model for Corrosion Applications

The surfaces of most metals immersed in aqueous electrolytes have a several-nanometer-thick oxide/hydroxide surface layer. This gives rise to the existence of both metal|oxide and oxide|liquid electrotlyte interfaces, and makes it challenging to correlate atomic length-scale structures with electrochemical properties such the potential-of-zero-charge (PZC). The PZC has been shown to be correlated the onset potential for pitting corrosion. Here, we conduct large-scale Density Functional Theory and ab initio molecular dynamics to calculate the PZC of a Al(111)| γ -Al 2 O 3 (110)| water double-interface model within the context of aluminum corrosion. By partitioning the multiple interfaces involved into binary components with additive contributions to the overall work function and voltage, we predict the PZC to be -1.53 V vs SHE for this model. Furthermore, we calculate the orbital energy levels of defects like oxygen vacancies in the oxide, which are critical parameters in theories associated with pitting corrosion. We predict that the Fermi level at the PZC lies above the impurity defect levels of the oxygen vacancies, which are therefore uncharged at the PZC. From the PZC estimate, we predict the voltage needed to create oxygen vacancies with net positive charges within a flatband approximation.

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

Inelastic Neutron Spectra of Uranium Tetrafluoride Hydrate, UF 4 (H 2 O) 2.5

Uranium tetrafluoride hydrate (UFH) is formed by immersing anhydrous UF4 under water for 12 h. UFH is therefore clearly a chemical species of environmental concern, as anhydrous UF4 is an intermediate uranium form in the nuclear fuel cycle. We use inelastic neutron scattering (INS) to probe the full vibrational spectra of UFH and its deuterated analogue in an effort to improve the fundamental understanding of its vibrational spectra. Coupled with density functional theory (DFT) calculations, the first for this compound, and full spectral modeling, we generate the complete vibrational spectra of UFH and compare them to prior optical spectroscopic results. In particular, the combination of DFT with INS allows us to identify multiple distinct chemical environments in the water bending and OH stretching regions. Whereas the water molecules directly bound to the U atoms execute OH stretching around 3600 cm –1 , a second class of H-bonded waters vibrate below 3000 cm –1 , an indicator of strong H bonding. In addition, a class of librational water modes are observed between 400 and 900 cm–1, which themselves can be separated in energy according to their chemical environments. Furthermore, measurements presented herein directly assist in the assignment of certain spectral features in the infrared spectrum and will inform future investigations of UFH for environmental or forensics purposes.

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DOE OSTI2024

Redesigning Photoelectrodes So They Can Work in the Light and Dark

Unassisted photoelectrochemical (PEC) reactions, such as H2 generation and CO2 reduction, are limited by the durability of the immersed photoelectrode. Small band gap semiconductors, like Si, are efficient at utilizing a large portion of the solar spectrum but are not stable in aqueous environments without protection. While great strides have been made to improve stability under constant illumination, dark stability remains relatively unexamined and presents great challenges for durable PEC systems. Cathodic protection is an established electrochemical method for preventing metal electrode degradation in harsh conditions. Similar protection strategies cannot be applied to traditional two-terminal (2T) semiconductor photoelectrodes because of their inability to pass reverse bias current in the dark. New, three-terminal (3T) photovoltaic (PV) architectures introduce additional degrees of freedom in traditional 2T PEC operations by adding an extra electrical contact for an alternative low resistance path to protect the photoelectrode and drive electrochemical reactions, even in the dark. Here, we investigate bare 3T Si PV devices operating as photocathodes in aqueous methyl viologen electrolyte. The 3T architecture provides additional capabilities to PEC systems such as cathodic protection, the ability to drive reactions with or without illumination, and in situ switching between different operational modes. We show that 3T-based Si photocathodes maintain PEC activity after several hours of light/dark cycling. This work helps advance PEC use in real-world conditions where variable illumination must be considered.

cathodic protection↗
DOE OSTI2021

Effects of marine organic aerosols as sources of immersion-mode ice-nucleating particles on high-latitude mixed-phase clouds

Mixed-phase clouds are frequently observed in high-latitude regions and have important impacts on the surface energy budget and regional climate. Marine organic aerosol (MOA), a natural source of aerosol emitted over ~70 % of Earth's surface, may significantly modify the properties and radiative forcing of mixed-phase clouds. However, the relative importance of MOA as a source of ice-nucleating particles (INPs) in comparison to mineral dust, and MOA's effects as cloud condensation nuclei (CCN) and INPs on mixed-phase clouds are still open questions. In this study, we implement MOA as a new aerosol species into the Community Atmosphere Model version 6 (CAM6), the atmosphere component of the Community Earth System Model version 2 (CESM2), and allow the treatment of aerosol–cloud interactions of MOA via droplet activation and ice nucleation. CAM6 reproduces observed seasonal cycles of marine organic matter at Mace Head and Amsterdam Island when the MOA fraction of sea spray aerosol in the model is assumed to depend on sea spray biology but fails when this fraction is assumed to be constant. Model results indicate that marine INPs dominate primary ice nucleation below 400 hPa over the Southern Ocean and Arctic boundary layer, while dust INPs are more abundant elsewhere. By acting as CCN, MOA exerts a shortwave cloud forcing change of -2.78 W m-2 over the Southern Ocean in the austral summer. By acting as INPs, MOA enhances the longwave cloud forcing by 0.35 W m-2 over the Southern Ocean in the austral winter. The annual global mean net cloud forcing changes due to CCN and INPs of MOA are -0.35 and 0.016 W m-2, respectively. These findings highlight the vital importance for Earth system models to consider MOA as an important aerosol species for the interactions of biogeochemistry, hydrological cycle, and climate change.

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

Complex plant-derived organic aerosol as ice-nucleating particles – more than the sums of their parts?

Quantifying the impact of complex organic particles on the formation of ice crystals in clouds remains challenging, mostly due to the vast number of different sources ranging from sea spray to agricultural areas. In particular, there are many open questions regarding the ice nucleation properties of organic particles released from terrestrial sources such as decaying plant material. In this work, we present results from laboratory studies investigating the immersion freezing properties of individual organic compounds commonly found in plant tissue and complex organic aerosol particles from vegetated environments, without specifically investigating the contribution from biological particles, which may contribute to the overall ice nucleation efficiency observed at high temperatures. To characterize the ice nucleation properties of plant-related aerosol samples for temperatures between 242 and 267 K, we used the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) cloud chamber and the Ice Nucleation SpEctrometer of the Karlsruhe Institute of Technology (INSEKT), which is a droplet freezing assay. Individual plant components (polysaccharides, lignin, soy and rice protein) were mostly less ice active, or similarly ice active, compared to microcrystalline cellulose, which has been suggested by recent studies to be a proxy for quantifying the primary cloud ice formation caused by particles originating from vegetation. In contrast, samples from ambient sources with a complex organic matter composition (agricultural soils and leaf litter) were either similarly ice active or up to 2 orders of magnitude more ice active than cellulose. Of all individual organic plant components, only carnauba wax (i.e., lipids) showed a similarly high ice nucleation activity as that of the samples from vegetated environments over a temperature range between 245 and 252 K. Hence, based on our experimental results, we suggest considering cellulose as being representative for the average ice nucleation activity of plant-derived particles, whereas lignin and plant proteins tend to provide a lower limit. In contrast, complex biogenic particles may exhibit ice nucleation activities which are up to 2 orders of magnitude higher than observed for cellulose, making ambient plant-derived particles a potentially important contributor to the population of ice-nucleating particles in the troposphere, even though major uncertainties regarding their transport to cloud altitude remain.

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