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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 1,297 records · Page 72
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Multivalent ions induce lateral structural inhomogeneities in polyelectrolyte brushes

Subtle details about a polyelectrolyte’s surrounding environment can dictate its structural features and potential applications. Atomic force microscopy (AFM), surface forces apparatus (SFA) measurements, and coarse-grained molecular dynamics simulations are combined to study the structure of planar polyelectrolyte brushes [poly(styrenesulfonate), PSS] in a variety of solvent conditions. More specifically, AFM images provide a first direct visualization of lateral inhomogeneities on the surface of polyelectrolyte brushes collapsed in solutions containing trivalent counterions. These images are interpreted in the context of a coarse-grained molecular model and are corroborated by accompanying interaction force measurements with the SFA. Our findings indicate that lateral inhomogeneities are absent from PSS brush layers collapsed in a poor solvent without multivalent ions. Together, AFM, SFA, and our molecular model present a detailed picture in which solvophobic and multivalent ion–induced effects work in concert to drive strong phase separation, with electrostatic bridging of polyelectrolyte chains playing an essential role in the collapsed structure formation.

42 ENGINEERING↗
DOE OSTI2021

Self-organization of nanoparticles and molecules in periodic Liesegang-type structures

Chemical organization in reaction-diffusion systems offers a strategy for the generation of materials with ordered morphologies and structural hierarchy. Periodic structures are formed by either molecules or nanoparticles. On the premise of new directing factors and materials, an emerging frontier is the design of systems in which the precipitation partners are nanoparticles and molecules. We show that solvent evaporation from a suspension of cellulose nanocrystals (CNCs) and L -(+)-tartaric acid [ L -(+)-TA] causes phase separation and precipitation, which, being coupled with a reaction/diffusion, results in rhythmic alternation of CNC-rich and L -(+)-TA–rich rings. The CNC-rich regions have a cholesteric structure, while the L -(+)-TA–rich bands are formed by radially aligned elongated bundles. The moving edge of the pattern propagates with a finite constant velocity, which enables control of periodicity by varying film preparation conditions. This work expands knowledge about self-organizing reaction-diffusion systems and offers a strategy for the design of self-organizing materials.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Spatially resolved structural order in low-temperature liquid electrolyte

Determining the degree and the spatial extent of structural order in liquids is a grand challenge. Here, we are able to resolve the structural order in a model organic electrolyte of 1 M lithium hexafluorophosphate (LiP 6 ) dissolved in 1:1 (v/v) ethylene carbonate:diethylcarbonate by developing an integrated method of liquid-phase transmission electron microscopy (TEM), cryo-TEM operated at -30°C, four-dimensional scanning TEM, and data analysis based on deep learning. This study reveals the presence of short-range order (SRO) in the high–salt concentration domains of the liquid electrolyte from liquid phase separation at the low temperature. Molecular dynamics simulations suggest the SRO originates from the Li + - (PF 6 - ) n (n > 2) local structural order induced by high LiP 6 salt concentration.

42 ENGINEERING↗
DOE OSTI2023

Thin film design of amorphous hafnium oxide nanocomposites enabling strong interfacial resistive switching uniformity

A design concept of phase-separated amorphous nanocomposite thin films is presented that realizes interfacial resistive switching (RS) in hafnium-oxide-based devices. The films are formed by incorporating an average of 7% Ba into hafnium oxide during pulsed laser deposition at temperatures ≤400°C. The added Ba prevents the films from crystallizing and leads to ~20-nm-thin films consisting of an amorphous HfO x host matrix interspersed with ~2-nm-wide, ~5-to-10-nm-pitch Ba-rich amorphous nanocolumns penetrating approximately two-thirds through the films. This restricts the RS to an interfacial Schottky-like energy barrier whose magnitude is tuned by ionic migration under an applied electric field. Resulting devices achieve stable cycle-to-cycle, device-to-device, and sample-to-sample reproducibility with a measured switching endurance of ≥10 4 cycles for a memory window ≥10 at switching voltages of ±2 V. Each device can be set to multiple intermediate resistance states, which enables synaptic spike-timing–dependent plasticity. The presented concept unlocks additional design variables for RS devices.

36 MATERIALS SCIENCE↗
DOE OSTI2023

High-temperature low-humidity proton exchange membrane with “stream-reservoir” ionic channels for high-power-density fuel cells

The perfluorosulfonic acid (PFSA) proton exchange membrane (PEM) is the key component for hydrogen fuel cells (FCs). We used in situ synchrotron scattering to investigate the PEM morphology evolution and found a “stream-reservoir” morphology, which enables efficient proton transport. The short-side-chain (SSC) PFSA PEM is fabricated under the guidance of morphology optimization, which delivered a proton conductivity of 193 milliSiemens per centimeter [95% relativity humidity (RH)] and 40 milliSiemens per centimeter (40% RH) at 80°C. The improved glass transition temperature, water permeability, and mechanical strength enable high-temperature low-humidity FC applications. Performance improvement by 82.3% at 110°C and 25% RH is obtained for SSC-PFSA PEM FCs compared to Nafion polymer PEM devices. The insights in chain conformation, packing mechanism, crystallization, and phase separation of PFSAs build up the structure-property relationship. In addition, SSC-PFSA PEM is ideal for high-temperature low-humidity FCs that are needed urgently for high-power-density and heavy-duty applications.

25 ENERGY STORAGE↗
DOE OSTI2024

Design of intrinsically disordered protein variants with diverse structural properties

Intrinsically disordered proteins (IDPs) perform a broad range of functions in biology, suggesting that the ability to design IDPs could help expand the repertoire of proteins with novel functions. Computational design of IDPs with specific conformational properties has, however, been difficult because of their substantial dynamics and structural complexity. We describe a general algorithm for designing IDPs with specific structural properties. We demonstrate the power of the algorithm by generating variants of naturally occurring IDPs that differ in compaction, long-range contacts, and propensity to phase separate. We experimentally tested and validated our designs and analyzed the sequence features that determine conformations. We show how our results are captured by a machine learning model, enabling us to speed up the algorithm. Our work expands the toolbox for computational protein design and will facilitate the design of proteins whose functions exploit the many properties afforded by protein disorder.

Science & Technology - Other Topics↗
DOE OSTI2022

Dynamics of active liquid interfaces

Controlling interfaces of phase-separating fluid mixtures is key to the creation of diverse functional soft materials. Traditionally, this is accomplished with surface-modifying chemical agents. Using experiment and theory, we studied how mechanical activity shapes soft interfaces that separate an active and a passive fluid. Chaotic flows in the active fluid give rise to giant interfacial fluctuations and noninertial propagating active waves. At high activities, stresses disrupt interface continuity and drive droplet generation, producing an emulsion-like active state composed of finite-sized droplets. When in contact with a solid boundary, active interfaces exhibit nonequilibrium wetting transitions, in which the fluid climbs the wall against gravity. These results demonstrate the promise of mechanically driven interfaces for creating a new class of soft active matter.

Science & Technology - Other Topics↗
DOE OSTI2022

Transcriptomic Data Sets for Zymomonas mobilis 2032 during Fermentation of Ammonia Fiber Expansion (AFEX)-Pretreated Corn Stover and Switchgrass Hydrolysates

The transcriptomes of Zymomonas mobilis 2032 were captured during the fermentation of ammonia fiber expansion (AFEX)-pretreated corn stover and switchgrass hydrolysates containing different concentrations of glucose and xylose. RNA samples were collected when Z. mobilis was fermenting glucose or xylose. Here, we present transcriptome sequencing (RNA-Seq) data obtained during separate phases of glucose or xylose consumption.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Local Structure of Fe–Cr Powders Prepared by Mechanical Alloying

We have studied the structure of Fe–Cr alloys prepared by mechanical alloying. According to X-ray diffraction data, all of the alloys are single-phase and consist of a BCC solid solution. The local structure of the alloys has been studied by Mössbauer spectroscopy. Analysis of the local environment of the Fe atoms leads us to assume clustering processes in the alloy containing 20 at % Cr and suggests that the alloys containing 35 and 50 at % Cr experience phase separation into regions of a homogeneous disordered chromium- enriched solid solution and an iron-enriched imperfect structure containing a considerable amount of dissolved gases.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Effect of Ag in CdSe thin films prepared using thermal evaporation

It has been a general practice to dope thin films with suitable dopants to modify the properties of the films to make them more suitable for potential applications. When the dopant concentrations are low, they do not normally affect the structure and morphology of the films. However, it may lead to drastic changes in electronic properties of the films. This might result from the dopant getting incorporated into the lattice of the material of the films. Cadmium selenide is an important compound semiconductor material with an attractive energy band gap. The present work relates to an attempt made to dope CdSe thin films with silver. CdSe:Ag (1–5%) thin films were deposited on glass substrates at an optimized substrate temperature of 453 K using thermal evaporation technique. The grown films were analyzed using X-ray diffraction, scanning electron microscopy (SEM), energy dispersive analysis of X-ray (EDX) techniques. It is observed that undoped CdSe thin films and CdSe:Ag films have hexagonal structure. The grain size was found to increase marginally with an increase in the Ag concentration. The optical band gap of the films determined by optical transmission measurements agree with that of CdSe. Electrical conductivity is observed to increase from 10{sup –4} to 3.66 (Ω cm){sup –1} on addition of silver. The variation of resistance with temperature indicates that the prepared films consist of CdSe and Ag existing as two separate phases coexisting and contributing individually to the resistivity of the films.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Influence of europium doping on magnetic properties of 3D topological semimetal Cd{sub 3}As{sub 2} from ESR data

Influence of weak doping by rare-earth elements on magnetic and transport properties of a 3D topological semimetal Cd{sub 3}As{sub 2} was studied experimentally. In particular, the doping by europium causes to change of the magnetoresistance sign from positive to negative. First measurements of electron spin resonance and magnetic susceptibility have shown that there are two types of Eu{sup 2+} magnetic ions that occupy the positions of cadmium ions and tetrahedral vacancies and form the ferromagnetic and antiferromagnetic phases, respectively. These facts give an evidence of small-scaled phase separation and a transformation of the Dirac semimetal to a Weyl semimetal induced by magnetic impurities.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Frozen Superparaelectric State of Local Polar Regions in GdMn{sub 2}O{sub 5} and Gd{sub 0.8}Ce{sub 0.2}MnO{sub 5}

A comparative study of the dielectric properties and electric polarization of multiferroics GdMn{sub 2}O{sub 5} and Gd{sub 0.8}Ce{sub 0.2}MnO{sub 5} has been carried out in the temperature range 5–330 K. The polarization properties in the ferroelectric state that forms due to a charge ordering and exchange striction have been studied at T ≤ T{sub C} = 30 K. The properties of the restricted polar phase separation domains formed in the crystals containing ions Mn{sup 3+} and Mn{sup 4+} have been studied, too. These domains exhibit the electric polarization in the temperature range from 5 K to some temperatures T{sub f} ≫ T{sub C}. Such a high-temperature polarization is due to the frozen superparaelectric state of the restricted polar domains.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Magnetic Properties of Eu{sub 0.9}Yb{sub 0.1}B{sub 6}

The magnetic properties of substitutional solid solutions Eu{sub 0.9}Yb{sub 0.1}B{sub 6} have been investigated in the temperature range of 2–300 K in fields up to 5 T. The data obtained confirm that the state with the electronic and magnetic phase separation (typical of europium hexaboride) is implemented in Eu{sub 0.9}Yb{sub 0.1}B{sub 6} when the system metallization (T{sub M} ≈ 15 K) precedes the ferromagnetic ordering (T{sub C} ≈ 11.4 K). An analysis of the curves M(H) in the Belov–Arrott coordinates makes it possible to evaluate spontaneous magnetization M{sub sp} and zero field susceptibility χ{sub 0} and determine the character of their critical behavior near the Curie point. The calculated critical indices (γ ≈ 1.28 and β ≈ 0.34) are in agreement with the predictions of the three-dimensional Heisenberg model.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Competition between the Spin and Pseudospin Subsystems in a Model Cuprate

The competition between the magnetic and charge orderings in a model cuprate is considered in terms of a simplified static 2D spin–pseudospin model. This model is equivalent to the 2D dilute antiferromagnetic (AFM) Ising model with charged impurities. The mean-field approximation results are presented for the system under study and briefly compared to the classical Monte Carlo (MC) calculations. The numerical simulation shows that the cases of the strong exchange and the strong charge correlation differ qualitatively. In the case of a strong exchange, the AMF phase is instable with respect to the phase separation (PS) into the pseudospin (charge) and magnetic (spin) subsystems that behave as immiscible quantum liquids. The analytical expression has been obtained for the PS temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

What dielectric spectroscopy can tell us about supramolecular networks

Polymers which can form supramolecular networks are a promising class of materials to provide highly sought-after properties such as self-healing, enhanced mechanical strength, super-stretchability as well as easy recyclability. However, due to the vast range of possible chemical structures it is very demanding to optimize these materials for the desired performance. Consequently, a detailed understanding of the molecular processes that govern the macroscopic properties is paramount to their technological application. Here we discuss some telechelic model systems with hydrogen-bonding end groups and how dielectric spectroscopy in combination with linear oscillatory shear rheology helped to understand the association mechanism on a molecular scale, and verify the model of bond-lifetime renormalization. Furthermore, we analyze a limitation of these H-bonding polymers, namely that there is a trade-off between high plateau modulus and long terminal relaxation time --both cannot be maximized at the same time. Lastly, we show how more complex end groups phase separate from the main chain melt and thus lead to a more sophisticated rheological behavior which can overcome that limitation.

47 OTHER INSTRUMENTATION↗
DOE OSTI2019

Imaging Quantum Vortices in Superfluid Helium Droplets

Free superfluid helium droplets constitute a versatile medium for a diverse range of experiments in physics and chemistry that extend from studies of the fundamental laws of superfluid motion to the synthesis of novel nanomaterials. In particular, the emergence of quantum vortices in rotating helium droplets is one of the most dramatic hallmarks of superfluidity and gives detailed access to the wave function describing the quantum liquid. This review provides an introduction to quantum vorticity in helium droplets, followed by a historical account of experiments on vortex visualization in bulk superfluid helium and a more detailed discussion of recent advances in the study of the rotational motion of isolated, nano- to micrometer-scale superfluid helium droplets. Ultrafast X-ray and extreme ultraviolet scattering techniques enabled by X-ray free-electron lasers and high-order harmonic generation in particular have facilitated the in situ detection of droplet shapes and the imaging of vortex structures inside individual, isolated droplets. Here, new applications of helium droplets ranging from studies of quantum phase separations to mechanisms of low-temperature aggregation are discussed.

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

Reports From The Frontier: Overcoming Limitations for Pure-water Anion-exchange-membrane Electrolysis

Anion-exchange-membrane electrolysis is positioned to play a key role in the predicted exponential growth of green hydrogen technology with essential R&D advances. We reveal key design parameters essential to commercialization. First, stable alkaline oxygen-evolution reaction catalysts with high electronic conductivity and minimal surface reconstruction during operation must be designed. Alkaline catalyst layers must also be applied to the membrane electrode assembly with scalable, industrially relevant techniques. Second, ionomer oxidation mitigation strategies must be developed. Furthermore, this approach could also target other creative catalyst layer design, such as phase-separation control to protect oxidation-prone organic components or catalyst engineering to direct selectivity for hydroxide over polymer oxidation. If competitive efficiency and durability can be achieved in pure water, AEM electrolysis has the potential to become a dominant electrolyzer technology.

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

system2atoms

system2atoms is a suite of models that can simulate the performance of hydrogen infrastructure across multiple scales. Examples of the different scale levels include: 1. System Scale - techno-economic analysis for hydrogen applications, integration of hydrogen infrastructure with the electrical grid, and supply and demand constraints across applications 2. Component Scale - continuous-flow catalyst beds, electrochemical conversion units, gas-phase separators, pumps, compressors, storage tanks, evaporators, heaters, and coolers 3. Material Scale - surface reactions, degradation mechanisms, and catalyst poisoning

Mcnenly, MatthewJ↗