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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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A hydrophobic metal–organic framework displays some of the largest selectivities known for adsorption of the fluorinated greenhouse gases CF 4 and CHF 3 over N 2 .
We report the use of fluorinated polymer zwitterions to build hybrid systems for efficient CO 2 electroreduction.
The fluorinated pyridyl ligand [6-(CF 3 )-2-Py] − with gold( I ) affords trinuclear Au 3 assemblies that further organize into a supramolecular helical column through aurophilic interactions. Its chemistry with copper( I ) is even more remarkable, leading to an unprecedented octanuclear copper–pyridyl cluster complex featuring a central Cu 8 core with an approximate gyrobifastigium geometry. Solid powders of compounds {(6-(CF 3 )-2-Py)Au} 3 and {(6-(CF 3 )-2-Py)Cu} 8 exhibit intense photoluminescence at room temperature, displaying green and yellow colors to the naked eye, respectively. Here, the octanuclear copper complex is also an effective catalyst for azide–alkyne cycloaddition, producing triazoles. Detailed computational analyses confirm the preference for experimental geometries and provide insights into the observed luminescence.
This communication reports a method for the vinylogous radiofluorination of α-diazoacetates to generate [18F]-γ-fluoro-α,β-unsaturated esters and ketones in moderate to good radiochemical yields. The method uses no-carrier-added [18F]AgF and is compatible with aromatic and non-aromatic substrates and a number of different functional groups. The labeling method is showcased in the synthesis of a fluorinated cholest-5-en-3-one derivative as well as a difluorinated product pertinent to drug discovery.
Fluorinated ethylene propylene (FEP) films were made superhydrophobic by Ar + O{sub 2} plasma etching process. Field emission scanning electron microscopy and atomic force microscopy studies of the plasma-treated FEP samples detected the presence of uniformly distributed nano-protrusions exhibiting a low surface roughness necessary for maintaining the transparency of the samples. In fact, optical transmittance measurements showed an improvement in the transparency of FEP samples after plasma treatment. The X-ray photoelectron spectroscopic analysis showed the presence of –CF{sub x}–O–CF{sub x}– (x = 1, 2, or 3) linkages in both untreated and plasma-treated samples which explains the hydrophilic nature (contact angle below 90{sup ∘}) of the untreated sample. Fourier transform infrared spectroscopy showed no changes in the bulk properties of the plasma-treated samples. Moreover, exposure to the environment caused the surfaces to lose their superhydrophobic property in an indefinite amount of time. This has been further studied through a water immersion experiment and explained through the wetting state transition from Cassie state to Wenzel state.
Dielectric relaxation spectroscopy experiments were performed at high temperature on fluorinated parylene films during the occurrence of the isothermal crystalline phase transition. For this polymer, since the difference between the glass transition temperature (T{sub g}) and the phase transition temperature (T{sub c}) is very strong (T{sub c} ≥ 4T{sub g}), segmental and dipolar relaxation usually used to probe the crystallization are not shown in the experiment frequency window (10{sup −1} to 10{sup 6} Hz) during the crystallization. The charge diffusion becomes the only electrical marker that allows probing the phase transition. During the transition phase, a continuous decrease of about two orders of magnitude is observed in the conductivity values below an offset frequency (f{sub c}) with a tendency to stabilization after 600 min. Below the offset frequency, the decrease of the normalized conductivity to the initial value as function of time is frequency independent. The same behavior is also observed for the f{sub c} values that decrease from 160 Hz to about 20 Hz. Above the offset frequency, the electronic hopping mechanism is also affected by the phase transition and the power law exponent (n) of the AC conductivity shows a variation from 0.7 to 0.95 during the first 600 min that tend to stabilize thereafter. Accordingly, three parameters (n, f{sub c}, and AC conductivity values for frequencies below f{sub c}) extracted from the AC conductivity spectra in different frequency windows seem suitable to probe the crystalline phase transition.
We report poor fluorinated graphene sheets produced by thermal exfoliation embedding in carboxymethylcellulose polymer composite (GCMC) as an efficient mode locker for erbium doped fiber laser. Two GCMC mode lockers with different concentration have been fabricated. The GCMC based mode locked fiber laser shows stable soliton output pulse shaping with repetition rate of 28.5 MHz and output power of 5.5 mW was achieved with the high concentration GCMC, while a slightly higher output power of 6.9 mW was obtained using the low concentration GCMC mode locker.
The linear optical response and second harmonic generation (SHG) in alkali-metal/alkaline-earth-metal fluorine beryllium borate NaSr{sub 3}Be{sub 3}B{sub 3}O{sub 9}F{sub 4} are investigated by means of density functional theory. Calculations are performed using four types of exchange correlations: Ceperley-Alder local density approximation, Perdew Burke and Ernzerhof general gradient approximation, Engel-Vosko generalized gradient approximation, and the recently modified Becke-Johnson potential (mBJ). The mBJ approach brings the calculated band gap (7.20 eV) in excellent agreement with the experimental one (7.28 eV). The calculated values of the uniaxial anisotropy δε=−0.076 and the birefringence Δn(0)=0.052 indicate considerable anisotropy in the linear optical properties, which makes it favorable for the second harmonic generation. The dominant component of the second harmonic generation is χ{sub 111}{sup (2)}(ω). The value of |χ{sub 111}{sup (2)}(ω)| is about 1.2 pm/V at λ = 1064 nm in agreement with previous calculations. To analyze the origin of the high SHG of NaSr{sub 3}Be{sub 3}B{sub 3}O{sub 9}F{sub 4} single crystals, we have correlated the features of |χ{sub 111}{sup (2)}(ω)| spectra with the features of ε{sub 2}(ω) spectra as a function of ω/2 and ω. From the calculated dominant component |χ{sub 111}{sup (2)}(ω)|, we find that the microscopic first hyperpolarizability, β{sub 111}, the vector components along the dipole moment direction is 0.5 × 10{sup −30} esu at static limit and 0.6 × 10{sup −30} esu at λ = 1064 nm.
Measurements of electrical conductivity, electron work function, carrier mobility of holes and the diffusion length of excitons were performed on samples of conjugated polymers relevant to polymer solar cells. A state of the art fluorinated benzothiadiazole based conjugated copolymer (PBDT{sub THD} − DTBTff) was studied and benchmarked against the reference polymer poly-3-hexylthiophene (P3HT). We employed, respectively, four electrode conductivity measurements, Kelvin probe work function measurements, carrier mobility using charge extraction by linearly increasing voltage (CELIV) measurements and diffusion length determinaton using surface photovoltage measurements.
Using size-selected anion photoelectron spectroscopy and density functional theory, we investigated the structures and properties of fluorinated bimetallic clusters CoAuF 1-2 − and CuAuF 1-2 − and their neutrals. Both experimental and theoretical results show that in these cluster anions, Au behaves like a halogen atom. For example, the measured vertical detachment energies (VDEs) of CoAuF − (2.00 ± 0.08 eV) and CuAuF − (3.8 ± 0.1 eV) are close to those of CoF 2 − (2.12 ± 0.08 eV) and CuF 2 − (3.58 ± 0.08 eV), respectively. The theoretical results show that the geometries and electronic structures of CoAuF − and CuAuF − are similar to those of CoF 2 − and CuF 2 − . The natural population analysis and natural electron configuration analyses further confirm that the electronic properties of Au in MAuF − (M = Co, Cu) mimic those of MF 2 − . In addition, the electron localization function analyses show that the M-Au chemical bonds are similar to the corresponding M-F chemical bonds, providing evidence for the ionic nature of the interactions. When a second F atom is attached to the CoAuF − and CuAuF − clusters, the VDEs of the resulting CoAuF 2 − and CuAuF 2 − are 4.38 ± 0.08 eV and 3.71 ± 0.08 eV, respectively, indicating their superhalogen character as these values are higher than those of halogen anions. The results may be useful for understanding the properties of gold at the nanoscale that play an important role in catalysis and nanotechnology.
It is expected that the chemical properties of the heaviest of the superheavy elements (SHEs, = 113 – 118) do not align with what is suggested by their current positions on the periodic table. Specifically, the onset of significant relativistic effects, including increased spin–orbit splitting of the p-orbitals may lead to enhanced stability of low-oxidation states. Notably, it is predicted that flerovium ( = 114) may exhibit pseudo-noble gas behavior from a electron configuration that acts as an ‘inert pair’. Even though it is expected that the – splitting becomes pronounced toward the end of the p-block’s sixth row, there is currently limited experimental evidence to confirm its extent or impact. Here, the production of gas-phase lead ( = 82) and polonium ( = 84) fluoride cations (PbF and PoF ) were compared to elucidate differences in accessible oxidation states. The PoF and PbF species were produced and identified with the FIONA spectrometer at the Lawrence Berkeley National Laboratory 88-Inch Cylctron Facility. Polonium showed notably different fluorination chemistry than lead, producing PoF and PoF as primary products compared to lead’s PbF and PbF . The distribution of PoF products observed offer insights as to the role of spin–orbit splitting for polonium. Similar studies of superheavy elements would elucidate the accessibility of their low-oxidation states as well as to inform chemical predictions for eighth-row elements not yet discovered.
Directed self-assembly (DSA) of block copolymers (BCPs) Is one of the most promising techniques to tackle the ever-increasing demand for subllthographic features In semiconductor industries. BCPs with high Flory-Huggins parameter (chi) are of particular Interest due to their ability to self-assemble at the length scale of sub-10 nm. However, such high-chi BCPs typically have imbalanced surface energies between respective blocks, making it a challenge to achieve desired perpendicular orientation. To address this challenge, we mixed a fluorine-containing polymeric additive with poly(2-vlnylpyrldine)-block-polystyrene-block-poly(2-vlnylpyrldine) (P2VP-b-PS-b-P2VP) and successfully controlled the orientation of the high-chi triblock copolymer. The additive selectively mixes with P2VP block through hydrogen bonding and can reduce the dissimilarity of surface energies between PS and P2VP blocks. After optimizing additive dose and annealing conditions, desired perpendicular orientation formed upon simple thermal annealing. We further demonstrated DSA of this material system with five times density multiplication and a half-pitch as small as 8.5 nm. This material system Is also amenable to sequential Infiltration synthesis treatment to selectively grow metal oxide In P2VP domains, which can facilitate the subsequent pattern transfer. We believe that this integration-friendly DSA platform using simple thermal annealing holds the great potential for sub-10 nm nanopatterning applications.
Current research on ferroelectric polymers centers predominantly on poly(vinylidene fluoride) (PVDF)–based fluoropolymers because of their superior performance. However, they are considered “forever chemicals” with environmental concerns. Here, we describe a family of rationally designed fluorine-free ferroelectric polymers, featuring a polyoxypropylene main chain and disulfonyl alkyl side chains with a C3 spacer: −SO 2 CH 2 CHRCH 2 SO 2 − (R = −H or −CH 3 ). Both experimental and simulation results demonstrate that strong dipole-dipole interactions between neighboring disulfonyl groups induce ferroelectric ordering in the condensed state, which can be tailored by changing the R group: ferroelectric for R = −H or relaxor ferroelectric for R = −CH 3 . At low electric fields, the relaxor polymer exhibits electroactuation and electrocaloric performance comparable with those of state-of-the-art PVDF-based tetrapolymers.
Measurements of the L-shell X-ray emission of fluorine-like europium ions (Eu 54+ ) were made under controlled laboratory conditions on the EBIT-I electron beam ion trap at Livermore using an X-ray calorimeter, extending such measurements to the middle of the rare earth elements. Comparing the calorimeter spectra with atomic data from the flexible atomic code, we have identified and analyzed several prominent n = 3 → n = 2 transitions, including one two-electron, one-photon core changing transition and one electric quadrupole transition. We find that the measured energies are typically up to several eV higher than predicted.
Studies have shown fluorinated electrolyte solvents can form desirable solid electrolyte interphase (SEI) in lithium metal batteries. In this study, we develop a detailed mechanistic understanding of two high performing electrolytes, Fluoroethylene Carbonate (FEC) and Difluoroethylene Carbonate (DFEC) to demonstrate minimal structural variations can lead to different decomposition products, and thereby the nature of the SEI. Using density functional theory (DFT) calculations, we find different initial bond-breaking mechanisms between FEC and DFEC. We develop free energy diagrams for the decomposition pathways including both electrochemical and chemical steps. Using the computational Li electrode, we identify the largest limiting potential of 1.77 V for FEC decomposition, associated with the formation of lithium fluoride, lithium oxide and FEC oligomers, and 1.53 V for DFEC, which correspond to the formation of polymerized vinylene carbonate and lithium fluoride. We suggest the formation of oligomers in the case of FEC instead of long polymers may lead to better SEI compactness. We also demonstrate the SEI components of FEC and DFEC are not stable on typical cathode voltage (3.87 V). This study presents a unified electrocatalytic perspective on SEI formation and decomposition.
We report that preformation of graphite electrodes, in a highly fluorinated electrolyte, show exemplary performance when incorporated into LiNi 0.5 Mn 0.3 Co 0.2 O 2 //graphite cells (NMC//Gr) containing a traditional organic electrolyte. NMC//Gr cells, using preformed graphite electrodes, showed enhanced capacity and power retention as well as improved coulombic efficiencies. The increased performance was only observed with the use of specific electrolytes during the preforming step, where graphite electrodes, when preformed with the baseline organic carbonate electrolyte, did not show the same benefits. The identity of the preforming electrolyte was also observed to influence electrode crosstalk, where compounds generated at one electrode can affect the opposite electrode. The work herein presents both physical and electrochemical evidence of electrode crosstalk and reveals the beneficial effect of the preforming procedure in limiting the associated degradation mechanisms thereof. Lastly, the insights gained may lead to new methodologies for the design of electrochemically robust interfaces that can enabling high-voltage, lithium-ion batteries.
The mechanical properties of fluorinated thermoplastics (i.e., tensile strength and elongation) can vary with changes in injection molding processing parameters. Four fluoropolymers are examined: poly(vinylidene fluoride) (PVDF) and random poly(vinylidene fluoride-co-chlorotrifluoroethylene) (PVDF-CTFE) with three CTFE concentrations. Dog bones were manufactured with various cylinder dwell times and mold cooling times to assess the manufacturing sensitivity to the tensile response. Dwell and cooling times increasingly impact mechanical performance as CTFE concentration increases. Specimens exhibit higher tensile strength as a function of injection order. The first injected specimen exhibits the lowest tensile strength and highest elongation in all copolymers. This trend becomes more pronounced among fluoropolymers with higher CTFE concentration and lower weight-averaged molecular weight. Parallel plate rheology was used to obtain the zero-shear viscosity as a function of material type, process, and injection order. We found that in the copolymers, the first injected sample exhibited a lower zero-shear viscosity than the next, which indicates a lower molecular weight in the first injected specimen. This phenomenon was not present for the PVDF homopolymer. Copolymer mechanical uncertainties are hypothesized to result from the shorter molecular weight chains extruding out of the specimens’ sides as a flash due to higher mobility with CTFE segments.
The Li-S battery is a promising next-generation technology due to its high theoretical energy density (2600 Wh kg -1 ) and low active material cost. However, poor cycling stability and coulombic efficiency caused by polysulfide dissolution have proven to be major obstacles for a practical Li-S battery implementation. In this work, we develop a novel strategy to suppress polysulfide dissolution using hydrofluoroethers (HFEs) with bi-functional, amphiphlic surfactant-like design: a polar lithiophilic "head" attached to a fluorinated lithiophobic "tail." A unique solvation mechanism is proposed for these solvents whereby dissociated lithium ions are readily coordinated with lithiophilic "head" to induce self-assembly into micelle-like complex structures. Complex formation is verified experimentally by changing the additive structure and concentration using small angle X-ray scattering (SAXS). These HFE-based electrolytes are found to prevent polysulfide dissolution and to have excellent chemical compatibility with lithium metal: Li||Cu stripping/plating tests reveal high coulombic efficiency (>99.5%), modest polarization, and smooth surface morphology of the uniformly deposited lithium. Li-S cells are demonstrated with 1395 mAh g-1 initial capacity and 71.9% retention over 100 cycles at >99.5% efficiency-evidence that the micelle structure of the amphiphilic additives in HFEs can prohibit polysulfide dissolution while enabling facile Li + transport and anode passivation.