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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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Contrastive pretraining of chemical reactions by matching augmented reaction representations to improve machine learning performance on small reaction datasets.
We report that improving the morphology of bulk heterojunction active layers remains a primary challenge for organic photovoltaics (OPVs), and much research has been devoted to achieving this through modifying OPV casting solutions to control film formation and crystallinity. Yet, the solution conformation of conjugated polymers used in OPVs is largely unknown. Here, we report observations of temperature dependent aggregation (TDA) through small-angle X-ray scattering (SAXS) investigations of polymer conformation in chlorobenzene:dichlorobenzene casting solvent as a function of temperature for PffBT4T-2OD, a polymer known to display TDA, and its derivative PffBT3T-2OD which displays significantly reduced TDA. We find that, upon cooling below 80 °C, PffBT4T-2OD forms large crystalline aggregates in solution, while its derivative PffBT3T-2OD forms mostly amorphous aggregates of similar size with some evidence of short-range order. This change in solution aggregation behavior is reflected in the lack of gelation by PffBT3T-2OD upon film deposition by spin coating. Grazing-incidence wide-angle X-ray scattering (GIWAXS) revealed a preferred face-on π–π stacking orientation for PffBT3T-2OD films while PffBT4T-2OD's π–π stacking peak was isotropic. We combine these findings to suggest that the presence of crystalline seed aggregates in PffBT4T-2OD solution quickly form an isotropic crystallite network upon cooling while PffBT3T-2OD's amorphous aggregates more slowly crystallize resulting in improved processability of PffBT3T-2OD.
Weakly coupled molecular junctions are an active and important field of research due to their non-linear charge carrier transport. In this study, we investigate transport properties in a weakly coupled molecule, B 2 C 2 N 2 H 6 , using a combined quantum many-body approach and kinetic (master) equations. Various non-linear current–voltage characteristics such as negative differential conductance (NDC), rectifications, and Coulomb staircase, which are the hallmarks of multistate transport devices, have been obtained. We further explore the effect of different perturbations such as gate voltage and perpendicular magnetic field on molecular transport. Depending on the strength of the applied perturbing field, several phenomena such as current switching, and suppression of NDC, have been realized in the device. This study demonstrates small molecules as promising components in next-generation nano-devices.
The confinement of water molecules is vital in fields from biology to nanotechnology. The conditions allowing confinement in small finite polycyclic aromatic hydrocarbons (PAHs) are unclear, yet are crucial for understanding confinement in larger systems. Here, we report a computational study of water cluster confinement within PAHs dimers. Our results serve as a model for larger carbon allotropes and for understanding molecular interactions in confined systems. We identified size and structural motifs allowing confinement and demonstrated the motifs in various PAHs systems. Here we show that optimal OH∙∙∙π interactions between water clusters and the PAH dimer permit optimal confinement to occur. However, the lack of such interactions leads to the formation of CH∙∙∙O interactions, resulting in less ideal confinement. Confinement of layered clusters is also possible, provided that the optimal OH∙∙∙π interactions are conserved.
Novel σ– α method, applied under non-steady state conditions, enables an accelerated and detailed study of oxygen vacancy and small polaron transport in praseodymium doped ceria as functions of oxygen non-stoichiometry and temperature.
Here we report the presence of small clusters of atoms (<1 nm) (SCs) and single atoms (SAs) in solutions containing 1–2 nm dendrimer-encapsulated nanoparticles (DENs). Au and Pd DENs were imaged using aberration-corrected scanning transmission electron microscopy (ac-STEM), and energy dispersive spectroscopy (EDS) was used to identify and quantify the SAs/SCs. Two main findings have emerged from this work. First, the presence or absence of SAs/SCs depends on both the terminal functional group of the dendrimer (–NH 2 or –OH) and the elemental composition of the DENs (Au or Pd). Second, dialysis can be used to remove the majority of SAs/SCs in cases where a high density of SAs/SCs are present. The foregoing conclusions provide insights into the mechanisms for Au and Pd DEN synthesis and stability. Ultimately, these results demonstrate the need for careful characterization of systems containing nanoparticles to ensure that SAs/SCs, which may be below the detection limit of most analytical methods, are taken into consideration (especially for catalysis experiments).
A bifunctional small molecule BPM1 was synthesized. When BPM1 functions as an acceptor and a donor, the corresponding devices achieve the best PCEs of 7.1% and 14.8%, respectively, which are the highest values for OSCs based on bifunctional materials to date.
A case study on the thermal stability of polymerized small molecular acceptor (P50-γ) based PSCs was present. And the result demonstrated the thermal-disaggregation process of polymer donor PBDB-T plays a dominant role in the degenerative efficiency.
A series simple-structured small molecules of BR-X are used as third components in the binary blends of PM6:Y6 to achieve efficient ternary solar cells with enhanced PCEs up to 17.49%.
Mixtures of organic acids and amines have been studied extensively owing to their unusual physicochemical properties and applications as solvents for extraction. In equimolar ratios they represent pseudoprotic ionic liquids, and in other, “nonstoichiometric” ratios they display a range of odd physicochemical behaviors. We report the results of small-angle X-ray scattering studies of a series of such systems with a range of chemical structures chosen to explore the link between molecular geometry and the character of the emergent nanoscale local liquid structure. We find that while the details vary, structure can emerge even when the hydrogen-bonding character of the components is changed significantly, and the character of their hydrocarbon substituents is altered. The consistent emergence of local order in the face of varying chemical structures indicates that the process is robust. Furthermore, this implies that the emergence of such structure may in fact be far more common in liquid mixtures than is currently recognized, and a great many structures may be suitable for the synthesis of pseudoprotic ionic liquids.
Although the recent development of Y-series small-molecule acceptors (SMAs) has led to a dramatic increase in the power conversion efficiency (PCE) of organic solar cells (OSCs), the operational stability (device lifetime) of OSCs is inadequate for commercialization. In this study, we develop a new trimer acceptor (TYT), consisting of three Y-based molecules linked by electron-donating spacers, to realize an OSC with high-performance (PCE > 18%) and -stability (t 80% lifetime > 8000 h under 1 sun illumination, in which t 80% lifetime is the time required for the PCE of the OSC to reach 80% of its initial value). We demonstrate that the trimerization approach affords an acceptor, TYT, with an upshifted lowest unoccupied molecular orbital energy level, which, in turn, affords an efficient OSC with a high open-circuit voltage (0.964 V). In addition, the glass-transition temperature (T g ) of TYT (217 °C) is significantly higher than those of monomer (MYT, T g = 80 °C) and dimer (DYT, T g = 127 °C) acceptors, which effectively suppresses the molecular diffusion of TYT in a blend film with a polymer donor. Accordingly, a TYT-based OSC demonstrates a high PCE (18.2%) and long t 80% lifetime under 1 sun illumination (8454 h), outperforming MYT- and DYT-based OSCs that exhibit PCEs and t 80% lifetimes of 16.4% and 35 h, and 17.3% and 2551 h, respectively. Therefore, this study provides important guidelines for the design of electron acceptors in achieving OSCs with high performance and stability close to a commercial level.
Hydrate-based hydrogen storage is one of the most environmentally benign approaches to store hydrogen. Hydrogen storage capacity in hydrates relies on the occupancy of hydrogen molecules in the small and large cages.
Metal–organic nanotubes (MONTs) are porous, tunable 1D nanomaterials akin to metal–organic frameworks (MOFs). MONTs are synthesized via metal salts and coordinating ligands akin to MOFs, but crucially they are anisotropic, unlike most MOFs. Recently, MONTs have been shown to form statistically random copolymers; however, their mechanism of growth remains largely unexplored. Full realization of the potential of MONTs necessitates a thorough understanding of the mechanism of MONT growth. Herein, small-angle neutron scattering (SANS) was employed to investigate the copolymerization mechanism of two 1,2,4-ditriazole ligands and to quantify the inclusion of a solvent within the MONT pores. The results show parallelepiped-shaped structures are initially formed, which then aggregate to form larger lamellar structures. Additional experimentation with a deuterated ligand showed that the reactivities of all ligands are approximately equal, causing random ligand distribution within the resulting MONT. Finally, the results quantify the amount of solvent incorporated within the nanostructure pores at different stages of the formation process. These results show that early in the reaction the MONTs contain ca. 45% solvent, and they contain ca. 55% solvent late in the reaction when the MONTs are nearly fully formed.
Heterogeneous photocatalysts (PCs) have garnered attention for their sustainability and cost-effectiveness. Despite the existence of various types of these PCs, their synthesis often involves complex, multi-step procedures and laborious purification. Herein, we propose a simple method for attaching small-molecule photocatalytic species onto crosslinked 3-D polymer networks as insoluble scaffolds to create robust heterogeneous PCs. The highly swellable poly(ethylene glycol)-based ChemMatrix (CM) resin, known for its amphiphilic properties and high functional group loading, facilitated the covalent immobilization of the photoredox dye Eosin Y (EY), but also streamlined functionalization with Ir( III ) complexes. The resulting heterogeneous CM-EY demonstrated efficient photocatalytic performance in open-to-air dual photoredox catalysis of atom transfer radical polymerization (photo-ATRP) under green light. This was confirmed by the well-controlled synthesis of polymers with molecular masses ranging from 20 kDa to 300 kDa and low dispersities. Furthermore, CM-EY exhibited excellent photostability and recyclability over multiple cycles of ATRP. The heterogeneous catalysis of photo-ATRP provided high temporal control and enabled benign conditions for synthesizing protein-polymer hybrids (PPH). When combined with the initiator-modified CM (CM-BIB), CM-EY facilitated the solid-phase synthesis of homopolymers and block copolymers with recyclable performance. However, the coordinatively bound Ir@CM showed decreased catalytic activity and efficiency toward photoredox dehalogenation due to the leaching of active species during recycling. This study highlights the advantages of the covalent linking of catalysts to solid supports over non-covalent interactions, underscoring the potential of functionalized polymer resin as a promising scaffold. Such an approach offers customization and tunability, presenting opportunities for innovation in green chemistry.
The complex distribution of functional groups in carbohydrates, coupled with their strong solvation in water, makes them challenging targets for synthetic receptors. Despite extensive research into various molecular frameworks, most synthetic carbohydrate receptors have exhibited low affinities, and their interactions with sugars in aqueous environments remain poorly understood. In this work, we present a simple pyridinium-based hydrogen-bonding receptor derived from a subtle structural modification of a well-known tetralactam macrocycle. This small structural change resulted in a dramatic enhancement of glucose binding affinity, increasing from 56 M −1 to 3001 M −1 . Remarkably, the performance of our synthetic lectin surpasses that of the natural lectin, concanavalin A, by over fivefold. X-ray crystallography of the macrocycle–glucose complex reveals a distinctive hydrogen bonding pattern, which allows for a larger surface overlap between the receptor and glucose, contributing to the enhanced affinity. Furthermore, this receptor possesses allosteric binding sites, which involve chloride binding and trigger receptor aggregation. This unique allosteric process reveals the critical role of structural flexibility in this hydrogen-bonding receptor for the effective recognition of sugars. We also demonstrate the potential of this synthetic lectin as a highly sensitive glucose sensor in aqueous solutions.
Earlier we showed that in the molecular dynamics simulation of a rigid model of water it is necessary to use an integration time-step δ t ≤ 0.5 fs to ensure equipartition between translational and rotational modes. Here we extend that study in the NVT ensemble to NpT conditions and to an aqueous protein. We study neat liquid water with the rigid, SPC/E model and the protein BBA (PDB ID: 1FME) solvated in the rigid, TIP3P model. We examine integration time-steps ranging from 0.5 fs to 4.0 fs for various thermostat plus barostat combinations. We find that a small δ t is necessary to ensure consistent prediction of the simulation volume. Hydrogen mass repartitioning alleviates the problem somewhat, but is ineffective for the typical time-step used with this approach. The compressibility, a measure of volume fluctuations, and the dielectric constant, a measure of dipole moment fluctuations, are also seen to be sensitive to δ t . Using the mean volume estimated from the NpT simulation, we examine the electrostatic and van der Waals contribution to the hydration free energy of the protein in the NVT ensemble. These contributions are also sensitive to δ t . In going from δ t = 2 fs to δ t = 0.5 fs, the change in the net electrostatic plus van der Waals contribution to the hydration of BBA is already in excess of the folding free energy reported for this protein.
Lithium-ion battery cathodes are porous composites of active material, conductive carbon, and polymer binder. Controlling the cathode microstructure is key to achieving high energy density and cycling stability. Current characterization techniques lack the nanoscale resolution over representative volumes necessary to relate cathode microstructure to cycling performance. To address this challenge, we utilize contrast-variation small-angle neutron scattering to quantify the chemical and structural features of cathodes wet by dimethyl carbonate, representing a relevant solvent environment. Using neutron scattering measurements, we identify an expansion in carbon and polymer structures that arises after calendering and wetting with solvent. Further, we deconvolute the carbon and binder phases to obtain the solvent-accessible carbon black surface area, which we correlate to diminished capacity retention driven by electrolyte decomposition on exposed carbon. This technique provides nanoscale insight into composite cathode microstructures and resulting cycling performance, promising future applications to a broad range of porous materials that exist in energy storage systems.
We develop Monte Carlo simulations for uniformly charged polymers and a machine learning algorithm to interpret the intra-polymer structure factor of the charged polymer system, which can be obtained from small-angle scattering experiments. The polymer is modeled as a chain of fixed-length bonds, where the connected bonds are subject to bending energy, and there is also a screened Coulomb potential for charge interaction between all joints. The bending energy is determined by the intrinsic bending stiffness, and the charge interaction depends on the interaction strength and screening length. All three contribute to the stiffness of the polymer chain and lead to longer and larger polymer conformations. The screening length also introduces a second length scale for the polymer besides the bending persistence length. To obtain the inverse mapping from the structure factor to these polymer conformation and energy-related parameters, we generate a large data set of structure factors by running simulations for a wide range of polymer energy parameters. We use principal component analysis to investigate the intra-polymer structure factors and determine the feasibility of the inversion using the nearest neighbor distance. We employ Gaussian process regression to achieve the inverse mapping and extract the characteristic parameters of polymers from the structure factor with low relative error.