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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Dynamics of the water molecule density in a discharge chamber filled with a low-pressure humid gas

The dynamics of the H{sub 2}O molecule density in a metal gas-discharge chamber filled with low-pressure water vapor or its mixtures with noble gases was investigated by manometric and spectral methods. Regimes both with and without discharge excitation were studied. In the absence of a discharge, the molecule density dynamics is governed by the heterogeneous interaction of molecules with the chamber walls. In the presence of a discharge, in addition to the heterogeneous interaction, fast plasmachemical molecule dissociation also contributes to the initial stage of H{sub 2}O molecule loss. The role of heating of the chamber walls is discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Single Molecule Spectroelectrochemistry of Interfacial Charge Transfer Dynamics In Hybrid Organic Solar Cell

Our research under support of this DOE grant is focused on applied and fundamental aspects of model organic solar cell systems. Major accomplishments are: 1) we developed a spectroelectorchemistry technique of single molecule single nanoparticle method to study charge transfer between conjugated polymers and semiconductor at the single molecule level. The fluorescence of individual fluorescent polymers at semiconductor surfaces was shown to exhibit blinking behavior compared to molecules on glass substrates. Single molecule fluorescence excitation anisotropy measurements showed the conformation of the polymer molecules did not differ appreciably between glass and semiconductor substrates. The similarities in molecular conformation suggest that the observed differences in blinking activity are due to charge transfer between fluorescent polymer and semiconductor, which provides additional pathways between states of high and low fluorescence quantum efficiency. Similar spectroelectrochemistry work has been done for small organic dyes for understand their charge transfer dynamics on various substrates and electrochemical environments; 2) We developed a method of transferring semiconductor nanoparticles (NPs) and graphene oxide (GO) nanosheets into organic solvent for a potential electron acceptor in bulk heterojunction organic solar cells which employed polymer semiconductor as the electron donor. Electron transfer from the polymer semiconductor to semiconductor and GO in solutions and thin films was established through fluorescence spectroscopy and electroluminescence measurements. Solar cells containing these materials were constructed and evaluated using transient absorption spectroscopy and dynamic fluorescence techniques to understand the charge carrier generation and recombination events; 3) We invented a spectroelectorchemistry technique using light scattering and electroluminescence for rapid size determination and studying electrochemistry of single NPs in an electrochemical cell. For example, we are able to use this technique to track electroluminescence of single Au NPs, and the electrodeposition of individual Ag NPs in-situ. These metallic NPs are useful to enhance light harvesting in organic photovoltaic systems. The scattering at the surface of an indium tin oxide (ITO) working electrode was measured during a potential sweep. Utilizing Mie scattering theory and high resolution scanning electron microscopy (SEM), the scattering data were used to calculate current-potential curves depicting the electrodeposition of individual Ag NPs. The oxidation of individual presynthesized and electrodeposited Ag NPs was also investigated using fluorescence and DFS microscopies. Our work has produced 1 US provisional patent, 15 published manuscripts, 1 submitted and two additional in-writing manuscripts. 5 graduate students, 1 postdoctoral student, 1 visiting professor, and two undergraduate students have received research training in the area of electrochemistry and optical spectroscopy under support of this award.

14 SOLAR ENERGY↗
DOE OSTI2017

Growth and Destruction of PAH Molecules in Reactions with Carbon Atoms

A very high abundance of atomic carbon in the interstellar medium (ISM), and the high reactivity of these species toward different hydrocarbon molecules including benzene, raise questions regarding the stability of polycyclic aromatic hydrocarbon (PAH) molecules in space. To test the efficiency of destruction of PAH molecules via reactions with atomic carbon, we performed a set of laboratory and computational studies of the reactions of naphthalene, anthracene, and coronene molecules with carbon atoms in the ground state. The reactions were investigated in liquid helium droplets at T = 0.37 K and by quantum chemical computations. Our studies suggest that all small and all large catacondensed PAHs react barrierlessly with atomic carbon, and therefore should be efficiently destroyed by such reactions in a broad temperature range. At the same time, large compact pericondensed PAHs should be more inert toward such a reaction. In addition, taking into account their higher photostability, much higher abundances of pericondensed PAHs should be expected in various astrophysical environments. The barrierless reactions between carbon atoms and small PAHs also suggest that, in the ISM, these reactions could lead to the bottom-up formation of PAH molecules.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2007

The Chemistry of Multiply Deuterated Molecules in Protoplanetary Disks: I. The Outer Disk

We present new models of the deuterium chemistry in protoplanetary disks, including, for the first time, multiply deuterated species. We use these models to explore whether observations in combination with models can give us clues as to which desorption processes occur in disks.We find, in common with other authors, that photodesorption can allow strongly bound molecules such as HDO to exist in the gas phase in a layer above the midplane. Models including this process give the best agreement with the observations. In the midplane, cosmic-ray heating can desorb weakly bound molecules such as CO and N2. We find the observations suggest that N2 is gaseous in this region, but that CO must be retained on the grains to account for the observed DCO+/HCO+. This could be achieved by CO having a higher binding energy than N2 (as may be the case when these molecules are accreted onto water ice) or by a smaller cosmic-ray desorption rate for CO than assumed here, as suggested by recent theoretical work. For gaseous molecules the calculated deuteration can be greatly changed by chemical processing in the disk from the input molecular cloud values. On the grains singly deuterated species tend to retain the D/H ratio set in the molecular cloud, whereas multiply deuterated species are more affected by the disk chemistry. Consequently, the D/H ratios observed in comets may be partly set in the parent cloud and partly in the disk, depending on the molecule.

circumstellar matter↗
DOE OSTI2013

Single Molecule Junctions: Probing Contact Chemistry and Fundamental Circuit Laws

By exploiting selective link chemistry, formation of single molecule junctions with reproducible conductance has become established. Systematic studies reveal the structure-conductance relationships for diverse molecules. I will draw on experiments from my collaborators at Columbia University, atomic-scale calculations and theory to describe progress in two areas. First, I will describe a novel route to form single molecule junctions, based on SnMe3 terminated molecules, in which gold directly bonds to carbon in the molecule backbone resulting in near ideal contact resistance [1]. Second, comparison of the conductance of junctions formed with molecular species containing either one backbone or two backbones in parallel allows demonstration of the role of quantum interference in the conductance superposition law at the molecular scale [2].

36 MATERIALS SCIENCE↗
DOE OSTI2014

Electrical, Mechanical and Thermal Properties of Single Molecules

The specific aims of the prior DOE grant are to determine the stability of a single molecule bound to two electrodes, study local heating in single molecule junctions due to electron-phonon and electron-electron interactions, measure electron-phonon interactions in single molecule wires; and explore piezoelectric properties of single molecules. We have completed all the major tasks, and also expanded naturally the scope of the project to address several other critical issues in single molecule properties, developed new experimental capabilities, and observed a number of unexpected phenomena. We summarized here some of the findings that are most relevant to the present renewal proposal. More details can be found in the publications resulted from this grant and annual progress reports.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Semiconducting Small Molecules as Active Materials for p-Type Accumulation Mode Organic Electrochemical Transistors

A series of semiconducting small molecules with bithiophene or bis-3,4-ethylenedioxythiophene cores are designed and synthesized. The molecules display stable reversible oxidation in solution and can be reversibly oxidized in the solid state with aqueous electrolyte when functionalized with polar triethylene glycol side chains. Evidence of promising ion injection properties observed with cyclic voltammetry is complemented by strong electrochromism probed by spectroelectrochemistry. Blending these molecules with high molecular weight polyethylene oxide (PEO) is found to improve both ion injection and thin film stability. The molecules and their corresponding PEO blends are investigated as active layers in organic electrochemical transistors (OECTs). For the most promising molecule:polymer blend (P4E4:PEO), p-type accumulation mode OECTs with µA drain currents, μS peak transconductances, and a µC* figure-of-merit value of 0.81 F V -1 cm -1 s -1 are obtained.

36 MATERIALS SCIENCE↗
DOE OSTI2023

The hydrogen bond between tryptophan and the host molecule induced fluorescence enhancement

Abstract Tryptophan is one of important amino acids in the human body, therefore its detection is particularly important. The 3,5‐bis(4‐pyridyl)‐4‐amino‐1,2,4‐triazole (BPAT) organic molecule was designed to be used as fluorescence detectors to detect tryptophan molecules for the interaction between the host and the guest. BPAT shows good sensitivity and selectivity towards tryptophan compared with other amino acid molecules. The limit of detection obtained from formula 3δ/K SV is considered to be 5.43 × 10 −7 mol/L. We speculated that this change is mainly caused by the hydrogen bond between tryptophan and the host molecule BPAT. This conjecture was verified by the controlled experiments with other host molecules.

Yang, Xi↗
DOE OSTI2025

Layers Can Be Deceiving: A Hopping Model for Small Molecule Diffusion in TATB Crystal

Sorption of small molecule gases in materials can play a significant role in their long‐term stability and compatibility within multi‐material assemblies. While many material properties of the insensitive high explosive TATB (1,3,5‐triamino‐2,4,6‐trinitrobenzene) are well understood, very little is known regarding its permeability to gases. TATB crystal exhibits a graphitic‐like layered packing structure that evokes a mental schema in which the layers form nanoscopic channels, but it is unclear whether this structure promotes gas transport. Here, we use molecular dynamics (MD) simulations to predict transport of small molecules through TATB single crystal. An approach to fit classical force fields is developed to model TATB interactions with H 2 O, He, Ne, and Ar, which is then combined with steered MD to probe gas transport along selected directions in the crystal. We find that small molecule transport occurs via a hopping mechanism that exhibits distinct jumps between interstitial sites and is substantially faster normal to the layers as compared to through them. This result stems from the finding that intralayer junctions between adjacent TATB molecules are the most stable interstitial sites and that energetic barriers are lower for hopping between adjacent layers. An empirical model for diffusion rate based on the MD data shows that the rate decays exponentially with increasing molecular radius and is negligibly small for all molecules larger than He, including common atmospheric gases. These findings have implications for the interpretation of experiments that measure surface area, material response to extreme conditions, and are expected to help constrain models for material aging.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Effect of Methyl Groups on Formation of Ordered or Layered Graphitic Materials from Aromatic Molecules

Abstract Developing functionally complex carbon materials from small aromatic molecules requires an understanding of how the chemistry and structure of its constituent molecules evolve and crosslink, to achieve a tailorable set of functional properties. Here, molecular dynamics (MD) simulations are used to isolate the effect of methyl groups on condensation reactions during the oxidative process and evaluate the impact on elastic modulus by considering three monodisperse pyrene‐based systems with increasing methyl group fraction. A parameter to quantify the reaction progression is designed by computing the number of new covalent bonds formed. Utilizing the previously developed MD framework, it is found that increasing methylation leads to an almost doubling of bond formation, a larger fraction of the new bonds oriented in the direction of tensile stress, and a higher basal plane alignment of the precursor molecules along the direction of tensile stress, resulting in enhanced tensile modulus. Additionally, via experiments, it is demonstrated that precursors with a higher fraction of methyl groups result in a higher alignment of molecules. Moreover, increased methylation results in the lower spread of single molecule alignment which may lead to smaller variations in tensile modulus and more consistent properties in carbon materials derived from methyl‐rich precursors.

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

OFraMP: a fragment-based tool to facilitate the parametrization of large molecules

Abstract An Online tool for Fragment-based Molecule Parametrization (OFraMP) is described. OFraMP is a web application for assigning atomic interaction parameters to large molecules by matching sub-fragments within the target molecule to equivalent sub-fragments within the Automated Topology Builder (ATB, atb.uq.edu.au) database. OFraMP identifies and compares alternative molecular fragments from the ATB database, which contains over 890,000 pre-parameterized molecules, using a novel hierarchical matching procedure. Atoms are considered within the context of an extended local environment (buffer region) with the degree of similarity between an atom in the target molecule and that in the proposed match controlled by varying the size of the buffer region. Adjacent matching atoms are combined into progressively larger matched sub-structures. The user then selects the most appropriate match. OFraMP also allows users to manually alter interaction parameters and automates the submission of missing substructures to the ATB in order to generate parameters for atoms in environments not represented in the existing database. The utility of OFraMP is illustrated using the anti-cancer agent paclitaxel and a dendrimer used in organic semiconductor devices. Graphical abstract OFraMP applied to paclitaxel (ATB ID 35922).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Prediction of Mass Spectral Response Factors from Predicted Chemometric Data for Druglike Molecules

A method is developed for the prediction of mass spectral ion counts of drug-like molecules using in silico calculated chemometric data. Various chemometric data, including polar and molecular surface areas, aqueous solvation free energies, and gas-phase and aqueous proton affinities were computed, and a statistically significant relationship between measured mass spectral ion counts and the combination of aqueous proton affinity and total molecular surface area was identified. In particular, through multilinear regression of ion counts on predicted chemometric data, we find that log{sub 10}(MS ion counts) = –4.824 + c{sub 1}•PA + c{sub 2}•SA, where PA is the aqueous proton affinity of the molecule computed at the SMD(aq)/M06-L/MIDI!//M06-L/MIDI! level of electronic structure theory, SA is the total surface area of the molecule in its conjugate base form, and c{sub 1} and c{sub 2} have values of –3.912 × 10{sup –2} mol kcal{sup –1} and 3.682 × 10{sup –3} Å{sup –2}. On a 66-molecule training set, this regression exhibits a multiple R value of 0.791 with p values for the intercept, c{sub 1}, and c{sub 2} of 1.4 × 10{sup –3}, 4.3 × 10{sup –10}, and 2.5 × 10{sup –6}, respectively. Application of this regression to an 11-molecule test set provides a good correlation of prediction with experiment (R = 0.905) albeit with a systematic underestimation of about 0.2 log units. This method may prove useful for semiquantitative analysis of drug metabolites for which MS response factors or authentic standards are not readily available. .

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Comparative energetics of carbon storage molecules in green algae

Several members of the green algae possess the ability to produce lipids and/or high value compounds in significant quantities. While for several of these green algal species induction of increased lipid production has been shown, and cultivation of species for high value molecules occurs at production scale, the molecular mechanisms governing over-accumulation of molecules synthesized from isoprenoid precursors, carotenoids, for example, have received far less attention. Here, we present a calculation of the required ATP equivalencies per carbon atom and reducing power equivalencies as NADH/NADPH (NAD(P)H) per carbon atom for the isoprenoid molecules ..beta..-carotene (C40), astaxanthin (C40), and squalene (C30). We compared energetic requirements of carbohydrates, triacylglycerol, and isoprenoid molecules under a gradient of conditions of cellular stress. Our calculations revealed slightly less ATP and NAD(P)H equivalency per carbon atom between triacylglycerol and the three isoprenoid molecules. Based on our results, we propose that the driving force for differences in accumulation patterns of carotenoids vs. triacylglycerols in algal cells under stress is largely dependent on the presence and regulation of bypass mechanisms at metabolic junction bottlenecks, like pyruvate dehydrogenase (PDH), within particular species. We provide a discussion of several molecular mechanisms that may influence carbon partitioning within different groups of green algae, including metabolic inhibition through accumulation of specific substrates related to ATP and reducing equivalent production (NAD(P)H) as well as cellular compartmentalization. This work contributes to the ongoing discussion of cellular homeostatic regulation during stress, as well as the potential mechanisms driving long-term carbon storage as it relates to energy and redox states within the algal cell.

09 BIOMASS FUELS↗
DOE OSTI2013

Confinement effects of solvation on a molecule physisorbed on a polarizable continuum particle

We investigate the effects of solvation on the static properties of a molecule physisorbed on a spherical polarizable continuum particle, with a static dielectric constant. The effective polarizability of the physisorbed molecule is enhanced by a factor of 105 in vacuo and by only 102 when solvated. The electrostatic interaction between molecules and the polarizable continuum particle (PCP) results in a magnified reflected electric field with a magnitude that depends on the PCP-molecule separation. A similar and greater magnification effect in reflected field also results from the PCP-field (external electric field) interaction. The variation of the polarizability of the molecules with respect to the changes in their environment illustrates the importance of electrostatic interaction in the enhancement of the effective polarizability. In the course of the investigation, the solute and the continuous body are represented with the same adaptive multi-wavelet basis functions, thereby, within the user specified precision, eliminating basis set error.

Chemistry↗
DOE OSTI2011

Water-inducing molecular self-assembly of amphiphilic molecules into nanofibers

Graphical abstract: TPDP nanofibers with smooth surfaces can be obtained by reprecipitation method using ethanol as good solvent and water as poor solvent. In the self-assembly process, during the water adding to the amphiphilic molecules' saturated solution, the amphiphilic molecules firstly assembled into needle-like small rods. With an increase in the self-assembled time, a large number of the nanofibers are produced. The assembly behavior was revealed in the course of direct in situ monitoring of its growth with optical microscopy. Highlights: Black-Right-Pointing-Pointer 2,3,6,7-Tetramethoxy-9,10-di(4-pyridyl)-9,10-dihydroanthracen (TPDP) was synthesized. Black-Right-Pointing-Pointer TPDP nanofibers can be obtained by reprecipitation method. Black-Right-Pointing-Pointer The assembly behavior was revealed in situ monitoring with optical microscopy. -- Abstract: We present investigations on the microcosmic self-assembly process of new synthesized amphiphilic TPDP molecules. It can be seen that pure TPDP nanofibers with smooth surfaces can be obtained by reprecipitation method using ethanol as good solvent and water as poor solvent. In the self-assembly process, during the water adding to the amphiphilic molecules' saturated solution, the amphiphilic molecules firstly assembled into needle-like small rods. With an increase in the self-assembled time, a large number of the nanofibers are produced. The assembly behavior was revealed in the course of direct in situ monitoring of its growth with optical microscopy. Field emission scanning electron microscopy was adopted to characterize the morphologies of the products.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Voltage Dependence of Molecule–Electrode Coupling in Biased Molecular Junctions

Biased interfaces between individual molecules and metallic electrodes are central in many nanoscale devices. A key quantity that governs the nature of the metal–molecule interface is the degree of hybridization between frontier orbitals of the molecule and electrode continuum states. This hybridization leads to the broadening of molecular resonances, a measure of the electronic coupling to the surface. In this work, we present detailed ab initio calculations of the evolution of this electronic coupling for selected frontier orbitals with bias voltage in molecular junctions, nanoscale devices where metal–molecule interface effects are dominant. We focus on symmetric and asymmetric junctions based on an experimentally well-studied system, Au–bipyridine–Au, as examples of our method. The nature of the bias-dependent coupling that emerges from our ab initio calculations provides new physical insight into experimentally achievable systems and is a marked quantitative improvement over simple Lorentzian models often used in interpreting device measurements. Beyond molecular junctions, our approach can be straightforwardly generalized to other molecule–metal interfaces.

Liu, Zhen-Fei↗
DOE OSTI2016

Excited Electron Dynamics at Semiconductor–Molecule Type-II Heterojunction Interface: First-Principles Dynamics Simulation

Excited electron dynamics at semiconductor–molecule interfaces is ubiquitous in various energy conversion technologies. However, a quantitative understanding of how molecular details influence the quantum dynamics of excited electrons remains a great scientific challenge because of the complex interplay of different processes with various time scales. Here in this paper, we employ first-principles electron dynamics simulations to investigate how molecular features govern the dynamics in a representative interface between the hydrogen-terminated Si(111) surface and a cyanidin molecule. Hot electron transfer to the chemisorbed molecule was observed but was short-lived on the molecule. Interfacial electron transfer to the chemisorbed molecule was found to be largely decoupled from hot electron relaxation within the semiconductor surface. While the hot electron relaxation was found to take place on a time scale of several hundred femtoseconds, the subsequent interfacial electron transfer was slower by an order of magnitude. Finally, at the same time, this secondary process of picosecond electron transfer is comparable in time scale to typical electron trapping into defect states in the energy gap.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Organic Semiconductor-Containing Supramolecules: Effect of Small Molecule Crystallization and Molecular Packing

Small molecules (SMs) with unique optical or electronic properties provide an opportunity to incorporate functionality into block copolymer (BCP)-based supramolecules. However, the assembly of supramolecules based on these highly crystalline molecules differs from their less crystalline counterparts. In this work, two families of organic semiconductor SMs are investigated, where the composition of the crystalline core, the location (side- vs end-functionalization) of the alkyl solubilizing groups, and the constitution (branched vs linear) of the alkyl groups are varied. With these SMs, we present a systematic study of how the phase behavior of the SMs affects the overall assembly of these organic semiconductor-based supramolecules. The incorporation of SMs has a large effect on the interfacial curvature, the supramolecular periodicity, and the overall supramolecular morphology. The crystal packing of the SM within the supramolecule does not necessarily lead to the assembly of the comb block within the BCP microdomains, as is normally observed for alkyl-containing supramolecules. An unusual lamellar morphology with a wavy interface between the microdomains is observed due to changes in the packing structure of the small molecule within BCP microdomains. Since the supramolecular approach is modular and small molecules can be readily switched out, present studies provide useful guidance toward access supramolecular assemblies over several length scales using optically active and semiconducting small molecules.

36 MATERIALS SCIENCE↗