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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Electrostatic Regolith Interaction Experiment (ERIE) Electrometer Initial Flight Results

The Electrostatic Regolith Interaction Experiment (ERIE) is a suborbital flight payload studying electrostatically charged dust particle dynamics under microgravity, jointly developed by University of Central Florida (UCF) and NASA Kennedy Space Center (KSC). ERIE combines components from two systems, the COLLisions Into Dust Experiment (COLLIDE) from UCF and the Wheel Electrostatic Spectrometer (WES) from NASA KSC, to advance understanding of charged grain behavior on low gravity bodies such as the Moon and asteroids. ERIE slides a door containing an electrometer system monitoring various insulating disks across the surface of a regolith simulant bed. The experiment is activated when the payload enters the microgravity potion of the flight. The grains in the simulant bed tribocharge via agitation during launch as well as through frictional interactions with the door and its protruding insulators. As the retention door retracts, particles are allowed to loft into an open volume, achieving motion due to electrostatic repulsion. The electrometer system measures the charge transfer between the granular material and the insulators. As the charged grains exit the bed, they travel through an applied electric field and a camera observes the kinematics of the individual grains whose trajectories are determined by their net charges. The design of the ERIE electrometer instrument and initial results from the first flight was presented at the 2021 AGU Fall Meeting under P55E-2002. Shortly after microgravity was achieved and the retaining door began to open, the rate of charge acquisition measured by the electrometer increased, indicating the insulators were accumulating triboelectric charge. Charged grains were observed in the video data to traverse across the external electric field and become deflected from a linear path due to their charges. Pairs of grains were also observed to orbit one another as expected from two oppositely charged bodies in proximity to one another. Improvements to the design of the instrument and preliminary results obtained from the second flight scheduled for Q3 2022 will be presented at this meeting.

Electrostatics↗
NASA NTRSDate not supplied

Electrostatic Regolith Interaction Experiment (ERIE) Electrometer Initial Flight Results

The Electrostatic Regolith Interaction Experiment (ERIE) is a suborbital flight payload studying electrostatically charged dust particle dynamics under microgravity, jointly developed by University of Central Florida (UCF) and NASA Kennedy Space Center (KSC). ERIE combines components from two systems, the COLLisions Into Dust Experiment (COLLIDE) from UCF and the Wheel Electrostatic Spectrometer (WES) from NASA KSC, to advance understanding of charged grain behavior on low gravity bodies such as the Moon and asteroids. ERIE slides a door containing an electrometer system monitoring various insulating disks across the surface of a regolith simulant bed. The experiment is activated when the payload enters the microgravity potion of the flight. The grains in the simulant bed tribocharge via agitation during launch as well as through frictional interactions with the door and its protruding insulators. As the retention door retracts, particles are allowed to loft into an open volume, achieving motion due to electrostatic repulsion. The electrometer system measures the charge transfer between the granular material and the insulators. As the charged grains exit the bed, they travel through an applied electric field and a camera observes the kinematics of the individual grains whose trajectories are determined by their net charges. The design of the ERIE electrometer instrument and initial results from the first flight was presented at the 2021 AGU Fall Meeting under P55E-2002. Shortly after microgravity was achieved and the retaining door began to open, the rate of charge acquisition measured by the electrometer increased, indicating the insulators were accumulating triboelectric charge. Charged grains were observed in the video data to traverse across the external electric field and become deflected from a linear path due to their charges. Pairs of grains were also observed to orbit one another as expected from two oppositely charged bodies in proximity to one another. Improvements to the design of the instrument and preliminary results obtained from the second flight scheduled for Q3 2022 will be presented at this meeting.

Electrostatics↗
DOE OSTI2020

Effects of Non-Electrostatic Intermolecular Interactions on the Phase Behavior of pH-Sensitive Polyelectrolyte Complexes

Polyelectrolyte complexes (PECs) offer enormous material tunability and desirable functionalities, and consequently have found broad utility in biomedical and material industries. While poly(acrylic acid) (PAA) and poly( allylamine hydrochloride) (PAH) are a commonly used pairing, various aspects of the phase behavior of PAA-PAH complexes have not been sufficiently quantified. In this work, we present a comprehensive experimental study depicting the binodal phase boundaries for the PAA-PAH complexes prepared under acidic, neutral, and basic conditions using thermogravimetric analysis, turbidimetry, and optical microscopy. Under neutral and basic conditions, phase behaviors of the complexes were largely similar to one another and followed general expectations of PEC phase behavior, except for unusually high resistance to disruption of the complex with added salt. Stable complexes are observed up to 4 M NaCl concentrations. Under acidic conditions, strikingly different phase behaviors of the PAA-PAH complexes were observed. The polymer content in the complex phase increased initially, followed by an expected decrease as salt was added to the complexes. This behavior may result from a combination of associative phase separation of PAA and PAH chains, influenced by electrostatic interactions, and segregative phase separation, which can be ascribed to the influence of a combination of the hydrophobic interactions of the aliphatic polymer backbone and the interpolymer hydrogen bonding of unionized acrylic monomer units. Our systematic investigations over a range of pH detailing these discrepancies in the PAA-PAH phase behavior are expected to clarify the inconsistencies among the reports in the literature and provide the material design strategies for practical use of the PAA-PAH complexes and multilayer assemblies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Simultaneous “Clean-and-Repair” of Surfaces Using Smart Droplets

An autonomous self-healing system, inspired by transportation processes inherent to biology, is described for materials transportation and repair. The selected model system combines inorganic nanoparticles (NPs) on damaged substrates with functional emulsion droplets that pick up the particles from pristine portions of the substrate and deposit them into damaged regions. The droplets are stabilized by polymer surfactants containing phosphorylcholine groups, a polymer composition selected to impart surfactant properties for droplet stabilization as well as fouling resistance to prevent irreversible droplet adsorption on the substrates. Both the NP pickup (cleaning) and drop off (repair) steps are conducted in a system driven by an imposed flow and characterized by fluorescence microscopy. To evaluate and optimize the efficiency of this NP transportation process, the effect of both the chemical composition of the polymer surfactant and the NP surface chemistry is investigated in this work. Interfacial interactions proved enabling for these NP transportation processes, specifically those involving NP/droplet, NP/substrate, and droplet/substrate interactions. Ultimately, droplets capable of both picking up and dropping off NPs are realized by adjusting fluid/fluid and fluid/substrate interactions, with electrostatic interactions between NPs and droplets proving most effective.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Silica nanocluster binding rate coefficients from molecular dynamics trajectory calculations

Oxide nanoparticle growth from vapor phase precursors occurs in high temperature aerosol reactors first via the formation of nanoclusters, which are nanometer-scale condensed-phase species composed of 10 1 -10 2 atoms. The binding rate for nanoclusters, defined as the rate at which two nanoclusters collide with and stick to one another, is hence of interest in predicting nanoparticle size distribution functions in an aerosol. We have utilized molecular dynamics (MD) trajectory calculations to determine the homogeneous (equal-sized) and heterogeneous (disparate-sized) binding rate coefficients of SiO2 (silica) nanoclusters composed of 18, 144, and 333 atoms. MD trajectory calculations incorporated all-atom models of nanoclusters using a combined Born–Huggins–Mayer-Lennard-Jones potential model, which accounts for both short range interactions and electrostatic interactions. MD calculations were utilized to determine the binding probability as a function of both initial relative velocity and impact parameter; integration of the binding probability across impact parameter and relative velocity space yields the binding rate coefficient. MD trajectory calculations reveal that the most common type of encounters between nanoclusters leading to binding are grazing collisions, i.e. instances where collision would not occur without induced dipole potential influences. The resulting binding rate coefficients are found to be extremely weakly dependent on system temperature, which is in contrast to the use of rate coefficient models which are the product of a hard-sphere collision rate coefficient and a constant enhancement factor (leading to a rate coefficient proportional to the square root of temperature). Enhancement factors defined from MD trajectory calculations fall in the range of 3–9 as system temperature decreases from 1500 K to 300 K. Furthermore, such large values suggest that potential interactions need to be considered when modeling oxide nanocluster growth in the gas phase.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Coarse-Grained Double-Stranded RNA Model from Quantum-Mechanical Calculations

A coarse-grained model for simulating structural properties of double-stranded RNA is developed with parameters obtained from quantum-mechanical calculations. This model follows previous parametrization for double stranded DNA, which is based on mapping the all-atom picture to a coarse-grained four-bead scheme. Chemical and structural differences between RNA and DNA have been taken into account for the model development. The parametrization is based on simulations using density functional theory (DFT) on separate units of the RNA molecule without implementing experimental data. The total energy is decomposed into four terms of physical significance: hydrogen bonding interaction, stacking interactions, backbone interactions, and electrostatic interactions. The first three interactions are treated within DFT, whereas the last one is included within a mean field approximation. Our double-stranded RNA coarse-grained model predicts stable helical structures for RNA. Other characteristics, such as structural or mechanical properties are reproduced with a very good accuracy. The development of the coarse-grained model for RNA allows extending the spatial and temporal length scales accessed by computer simulations and being able to model RNA-related biophysical processes, as well as novel RNA nanostructures.

Cruz-León, Sergio↗
DOE OSTI2018

Critical computational analysis illuminates the reductive-elimination mechanism that activates nitrogenase for N 2 reduction

Significance This report critically evaluates the mechanism by which nitrogenase cleaves the N≡N triple bond. It assesses the thermodynamic driving force provided by the accompanying, apparently “wasteful,” reductive elimination of an H 2 , and explains how the enzyme mechanistically couples exothermic H 2 formation to endothermic triple-bond cleavage in a nearly thermoneutral equilibrium process, thereby preventing the “futile” generation of two H 2 without N 2 reduction. This evaluation rests on a critical assessment of the density functional theory flavors needed to properly treat nitrogenase, and a demonstration that to prevent spurious disruption of FeMo-co upon 4[ e − /H + ] accumulation, one must employ a nitrogenase structural model that includes all residues interacting directly with FeMo-co, either via specific H-bond interactions, nonspecific electrostatic interactions, or steric confinement.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

A Printing-Centric Approach to the Electrostatic Modification of Polymer/Clay Composites for Use in 3D Direct-Ink Writing

Polymer/clay composite inks are exceptionally useful materials for fabrication processes based on 3D direct-ink writing, however, there remains an insufficient understanding of how their physiochemical dynamics impact printability. Using a model system, N-isopropylacrylamide/Laponite, the electrostatic interactions between Laponite platelets are modified to tune critical rheological properties in order to improve printability. Rheological measurements and X-ray scattering experiments are carried out to monitor the nano/micro-structural dynamics and complex physicochemical interactions of Laponite as it impacts complex modulus in the linear region, flow behavior, thixotropy, and yield stress of the composite ink. Modification of the electrostatic interactions between platelets reduces the yield stress of the material, while maintaining a complex microstructure that allows for sufficient recovery times upon removal of stress to form stable, and thus printable, filaments. A printing-centric approach is established based on a fundamental understanding of electrostatic inter-particle interactions, harnessing the innate microstructure of Laponite in 3D direct-ink writing of composites.

Rauzan, Brittany M.↗
DOE OSTI2019

Water adsorption on olivine(010) surfaces: Effect of alkali and transition metal cation doping

Dopants have the potential to locally modify water-olivine interactions, which can impact geological processes, such as weathering, CO 2 sequestration, and abiotic hydrocarbon generation. As a first step in understanding the role of dopants on the water structure and chemistry at water-olivine interfaces, water monomer adsorption on alkaline earth (AE) and transition metal (TM) doped forsterite(010) [Mg 2 SiO 4 (010)] surfaces was studied in this work using density functional theory (DFT). Dopants that occur in olivine minerals were considered and consisted of Ca, Sr, and Ba for the AE dopants and Cr, Mn, Fe, Co, and Ni for the TM dopants. The water molecule adsorbs on the olivine surface through a metal-water bond (Me–Ow) and a hydrogen bond with an adjacent surface lattice oxygen (Ox–Hw). A frontier orbital analysis reveals that the 1b 2 , 3a 1 , and 1b 1 (HOMO) of the water molecule are involved in the bonding. All of the TM dopants show strong net Me–Ow covalent bonding between 3a 1 and 1b 1 water orbitals and TM d states, while the AE dopants except for Mg 2 SiO 4 (010) show negligible Me–Ow covalent bonding. Both the AE and TM dopants show similar hydrogen bonding features involving both the 1b 2 and 3a 1 orbitals. While the AE cations show an overall lower Me–Ow covalent interaction, the AE dopants have strong electrostatic interactions between the positive metal cation and the negatively charged water dipole. A bonding model incorporating a linear combination of the covalent Me–Ow bond, the Ox–Hw hydrogen bond, the electrostatic interaction between the dopant cation and the H 2 O molecule, and the surface distortion energy is needed to capture the variation in the DFT adsorption energies on the olivine surfaces. The bonding analysis is able to identify the dominant contributions to water-dopant interactions and can serve as a basis for future studies of more realistic water-olivine interfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Molecular mechanism and binding free energy of doxorubicin intercalation in DNA

The intercalation process of binding doxorubicin (DOX) in DNA is studied by extensive MD simulations. Many molecular factors that control the binding affinity of DOX to DNA to form a stable complex are inspected and quantified by employing continuum solvation models for estimating the binding free energy. The modified MM-PB(GB)SA methodology provides a complete energetic profile of Δ G ele , Δ G vDW , Δ G polar , Δ G non-polar , T Δ S total , Δ G deform , Δ G con , and Δ G ion . To identify the sequence specificity of DOX, two different DNA sequences, d(CGATCG) or DNA1 and d(CGTACG) or DNA2, with one molecule (1 : 1 complex) or two molecule (2 : 1 complex) configurations of DOX were selected in this study. Our results show that the DNA deformation energy (Δ G deform ), the energy cost from translational and rotational entropic contributions ( T Δ S tran+rot ), the total electrostatic interactions (Δ G polar-PB/GB + Δ G ele ) of incorporation, the intramolecular electrostatic interactions (Δ G ele ) and electrostatic polar solvation interactions (Δ G polar-PB/GB ) are all unfavorable to the binding of DOX to DNA. However, they are overcome by at least five favorable interactions: the van der Waals interactions (Δ G vDW ), the non-polar solvation interaction (Δ G non-polar ), the vibrational entropic contribution ( T Δ S vib ), and the standard concentration dependent free energies of DOX (Δ G con ) and the ionic solution (Δ G ion ). Specifically, the van der Waals interaction appears to be the major driving force to form a stable DOX–DNA complex. We also predict that DOX has stronger binding to DNA1 than DNA2. The DNA deformation penalty and entropy cost in the 2 : 1 complex are less than those in the 1 : 1 complex, thus they indicate that the 2 : 1 complex is more stable than the 1 : 1 complex. Here, we have calculated the total binding free energy (BFE) (Δ G t-sim ) using both MM-PBSA and MM-GBSA methods, which suggests a more stable DOX–DNA complex at lower ionic concentration. The calculated BFE from the modified MM-GBSA method for DOX–DNA1 and DOX–DNA2 in the 1 : 1 complex is –9.1 and –5.1 kcal mol –1 respectively. The same quantities from the modified MM-PBSA method are –12.74 and –8.35 kcal mol –1 respectively. The value of the total BFE Δ G t-sim in the 1 : 1 complex is in reasonable agreement with the experimental value of –7.7 ± 0.3 kcal mol –1 .

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

Dynamic, Adaptive, Systems and Materials: Complex, Simple and Emergent Behaviors

This program has been funded by DoE/BES for twenty years. It has moved into and out of various subjects as it has developed, but it has retained its focus on complexity and complex systems. The project has evolved in the following way: Self-Assembly and Biomimetic Self-Assembly: All self-assembling systems depend upon a minimum of two types of interaction: a repulsion and an attraction. For the familiar molecular systems, attractive interactions are typically hydrogen bonds and electrostatic interactions. Repulsive interactions include steric effects, hydrophobic effects (in biological systems), and charge-charge repulsion. We have expanded this repertoire to include surface interactions, magnetic interactions, and others. I list these systems in the order in which we have explored them: i) A key emphasis in current work is in understanding how the movement of ions in a magnetic field (the Lorentz effect) interacts with catalytic systems. We have demonstrated that an acceleration in rate of reduction of CO 2 to CO can be accomplished by applying an external magnetic field. This acceleration is largely due to the application of the Lorentz effect on mass transport at the catalyst’s surface. ii) We have also extensively explored the influence of electrostatics, as exhibited in self-assembling systems, by tribocharging. iii) Another key system involves surface tension effects; examples include interactions between heavy particles floating at a liquid-air interface, and interacting by changes in surface area; interactions of bubbles and bubble rafts, behaviors of bubble trains in microfluidic networks, and behaviors of microorganisms in constraining environments. iv) This work has intentionally de-emphasized biological systems; but it does include some work on protein-ligand interactions and interactions among microorganisms. v) We have also explored applications of some of these effects, these explorations include bubble rafts as diffraction gratings, exploration of the structures that can be obtained by tribocharging and uses of these structures in exploring nucleation and melting of crystals. vi) Although not a major focus of this work, several other topics have emerged and offer opportunities for future work. These include the behavior of bubble trains and bubble rafts in microfluidic systems. A particularly interesting example is the formation of bubble trains that repeat in the alteration of large and small bubbles according to rules we do not presently understand, but are uniquely large-period oscillating systems. These systems offer a new route into understanding the instabilities of the type represented by oscillations. vii) We have also begun exploratory projects on magnetic levitation (especially to determine molecular density), and information storage (in molecules). Magnetic Levitation: Self-assembling and biomimetic systems require both attraction and repulsion. We have used electrostatics (tribocharging), interfacial free-energies (surface tension and related forces) and others. Potential uses include reconfigurable diffraction gratings and liquid lenses; exploration of mechanisms in tribocharging; tunneling in EGaIn junctions; and bubble trains (especially in micro-fluidic systems). Examples of systems representing these topics is included in the following papers: Complexity: Disks rotating at a water-air interface; Benard-Marangoni effects; Vortex-Crystals from spinning magnetic disks (Marangoni effects); EGaIn Electrode to study quantum tunneling; Self-Assembly of electrostatically-charged metallic spheres (electrets); Dynamically reconfigurable lens; Using computational designs of ligands for enzymes; Electrostatic self-assembly by tribocharging; Monodisperse bubble trains in microchannel systems; Inverted dripping faucet; Flames; Printing of micro-organisms to regenerate the “ink” of printing device; Using micro-organisms to move loads (“microoxen”); Motion of bacterial swarms near surfaces; Making monodisperse particles in microfluidic systems; Coding/decoding of information stored in droplet trains in microfluidic networks; Magnetic levitation; and Information storage. i) Tribocharging. The change in focus of this work on electrets from the fundamentals of charging to applications of these materials in studying self-assembly using electrostatic interactions. ii) Bubbles in Microchannels. The realization that systems of bubbles in microchannels represented a major opportunity to study complexity in a very tractable system, and the development of a semi-quantitative theory of this subject. iii) Flames. The growth of “flames” remains an exploratory subject for the research, although their currently relatively little active work involving it ongoing. iv) Systems with Microorganisms. The removal of work in biological systems from this project. Based on work supported in this program, we now have a significant project on the development of microfluidic tools for studying C. elegans (a nematode), but this work was not appropriate for a program focused on complexity, and we developed separate support for it. (It is, however, an example of successful seeding of a new area by BES.) The work on electrets has gone through a period in which a part of the program was the subject of a MURI; the focus of this work was to develop materials that did not charge electrostatically on friction or contact. The MURI is now over, and the work on dynamic self-assembly (supported by BES) is the major focus. “Flames” has also enjoyed synergistic support, in terms of a project supported by DARPA on flame suppression (in the absence of extinguishing agents, using acoustic and electrostatic interactions). This work was helpful in understanding some of the basics of flames, but is entirely distinct from the BES focus in complexity. A growing interest is in the Lorentz effect. The Lorentz effect is the force exerted on charged particles (electrons, ions, charged molecules) when they move through a perpendicular magnetic field. The Lorentz effect is almost ubiquitous in modern technology: examples of applications include electric motors, dynamos, cathode ray tubes, many batteries, and most systems that control electrical currents with magnetic forces. We have begun to explore the Lorentz effect in electrochemical systems and heterogeneous catalytic systems involving charged organic species and inorganic ions. This work is still at an early stage, but initial studies that Lorentz effects can be large when ions move through magnetic fields, or magnetic fields move in the presence of ions.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Three-Dimensional Tracking of Interfacial Hopping Diffusion

Theoretical predictions have suggested that molecular motion at interfaces—which influences processes including heterogeneous catalysis, (bio)chemical sensing, lubrication and adhesion, and nanomaterial self-assembly—may be dominated by hypothetical “hops” through the adjacent liquid phase, where a diffusing molecule readsorbs after a given hop according to a probabilistic “sticking coefficient.” Here, we use three-dimensional (3D) single-molecule tracking to explicitly visualize this process for human serum albumin at solid-liquid interfaces that exert varying electrostatic interactions on the biomacromolecule. Following desorption from the interface, a molecule experiences multiple unproductive surface encounters before readsorption. An average of approximately seven surface collisions is required for the repulsive surfaces, decreasing to approximately two and a half for surfaces that are more attractive. The hops themselves are also influenced by long-range interactions, with increased electrostatic repulsion causing hops of longer duration and distance. These findings explicitly demonstrate that interfacial diffusion is dominated by biased 3D Brownian motion involving bulk-surface coupling and that it can be controlled by influencing short- and long-range adsorbate-surface interactions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2026

pyEF: A Python Framework for QM and QM/MM Atom-Wise Electric Field Analysis

We introduce pyEF, a software package for computing molecular electric fields, electrostatic interaction energies, and electrostatic potentials from quantum mechanical (QM) atom-centered multipole expansions with atom-wise decomposable contributions. We demonstrate the computational efficiency and accuracy of this QM-derived electric field evaluation tool through several tests. To assess the influence of the underlying QM method and charge partitioning scheme on these electrostatic quantities, we analyze over 250 configurations of an acetone solute molecule in five solvents of variable polarity. We find that electric field calculations are highly sensitive to the choice of charge partitioning method. Even among real-space charge schemes, acetone Stark tuning rates differ by up to a factor of 2. Benchmarking computed solvent dipole moments against experimental bulk values, we conclude that the CM5, ADCH, and Hirshfeld-I charge schemes most reliably capture solvent electrostatics and therefore provide a more faithful foundation for computing electric fields. When constructed from these real-space charges, electric fields are nearly insensitive to basis set size and monotonically increase in magnitude with higher Fock exchange. We also demonstrate efficient convergence of QM electrostatics when more distant molecules are represented solely by MM point charges, reducing computational overhead. Leveraging these findings, we demonstrate the use of pyEF to deduce environmental effects on a transition metal complex from a Ga 4 L 6 12– nanocage and quantify the dominant role of organic linkers in orchestrating electrostatic preorganization.

electric fields↗
DOE OSTI2019

Electrostatic Influence on Photoisomerization in Bacteriorhodopsin and Halorhodopsin

Bacteriorhodopsin (bR) and halorhodopsin (hR) are mutual membrane proteins that transport ions across the cell membrane in halobacteria. Their ion transport function is triggered by photoactivated isomerization of the retinal protonated Schiff base (RPSB) chromophore. In spite of their similar structures, bR and hR exhibit widely differing RPSB isomerization rates and quantum yields (with bR being both faster and more efficient than hR). Previous simulations of photoisomerization in bR and hR using ab initio multiple spawning (AIMS) with QM/MM have successfully reproduced the experimentally observed ordering of quantum yields and isomerization rates, but the origin of these differences remains elusive. In this work, we discover the role of electrostatic interactions in the protein pocket surrounding RPSB. We probe the influence of protein electrostatics by modifying the charge of the complex counterion in bR/hR to be more/less negative than the native state. We find that such modifications lead to bR-like behavior in hR and vice versa. This demonstrates the crucial role of electrostatic interactions in controlling the outcome of RPSB photoisomerization.

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

Electrostatic-Assisted Liquefaction of Porous Carbons

Porous liquids are a newly developed porous material that combine unique fluidity with permanent porosity, which exhibit promising functionalities for a variety of applications. However, the apparent incompatibility between fluidity and permanent porosity makes the stabilization of porous nanoparticle with still empty pores in the dense liquid phase a significant challenging. For this study, by exploiting the electrostatic interaction between carbon networks and polymerized ionic liquids, we demonstrate that carbon-based porous nanoarchitectures can be well stabilized in liquids to afford permanent porosity, and thus opens up a new approach to prepare porous carbon liquids. Furthermore, we hope this facile synthesis strategy can be widely applicated to fabricate other types of porous liquids, such as those (e.g., carbon nitride, boron nitride, metal–organic frameworks, covalent organic frameworks etc.) also having the electrostatic interaction with polymerized ionic liquids, evidently advancing the development and understanding of porous liquids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Phosphonium-Based Polyzwitterions: Influence of Ionic Structure and Association on Mechanical Properties

This manuscript describes a synthetic strategy and structure–property investigation of unprecedented phosphonium-based zwitterionic homopolymers (polyzwitterions) and random copolymers (zwitterionomers). Free radical polymerization of 4-(diphenylphosphino)styrene (DPPS) provided neutral polymers containing reactive triarylphosphines. Quantitative postpolymerization alkylation of these pendant functionalities generated a library of polymers containing various concentrations of neutral phosphines, phosphonium ions, and phosphonium sulfobetaine zwitterions. The zwitterionic homo- and copolymers exhibited significantly higher glass transition temperatures (T g ) and enhanced mechanical reinforcement in comparison to neutral and phosphonium analogues. These changes in T g and mechanical properties were attributed to nanoscale morphological domains, which formed due to electrostatic interactions between zwitterionic groups, as revealed by X-ray scattering and broadband dielectric spectroscopy (BDS). BDS revealed increased static dielectric constants (>25) for the phosphonium zwitterionomers compared to ionomeric or neutral analogues. These high static dielectric constants for the solvent-free polyzwitterions supported their stronger polarization response in comparison with polymers containing neutral phosphines and phosphonium ions, and these interactions accounted for morphological differences and enhanced mechanical behavior. This work describes a versatile strategy for modulating electrostatic interactions with tunable mechanical properties for an unprecedented family of zwitterionic polymers.

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

Single-Molecule Detection of the Encounter and Productive Electron Transfer Complexes of a Photosynthetic Reaction Center

Small, diffusible redox proteins play an essential role in electron transfer (ET) in respiration and photosynthesis, sustaining life on Earth by shuttling electrons between membrane-bound complexes via finely tuned and reversible interactions. Ensemble kinetic studies show transient ET complexes form in two distinct stages: an “encounter” complex largely mediated by electrostatic interactions, which subsequently, through subtle reorganization of the binding interface, forms a “productive” ET complex stabilized by additional hydrophobic interactions around the redox-active cofactors. Here, using single-molecule force spectroscopy (SMFS) we dissected the transient ET complexes formed between the photosynthetic reaction center-light harvesting complex 1 (RC-LH1) of Rhodobacter sphaeroides and its native electron donor cytochrome c 2 (cyt c 2 ). Importantly, SMFS resolves the distribution of interaction forces into low (~150 pN) and high (~330 pN) components, with the former more susceptible to salt concentration and to alteration of key charged residues on the RC. Thus, the low force component is suggested to reflect the contribution of electrostatic interactions in forming the initial encounter complex, whereas the high force component reflects the additional stabilization provided by hydrophobic interactions to the productive ET complex. Employing molecular dynamics simulations, we resolve five intermediate states that comprise the encounter, productive ET and leaving complexes, predicting a weak interaction between cyt c 2 and the LH1 ring near the RC-L subunit that could lie along the exit path for oxidized cyt c 2 . The multimodal nature of the interactions of ET complexes captured here may have wider implications for ET in all domains of life.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗