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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Silver chlorobromide nanocubes with significantly improved uniformity: synthesis and assembly into photonic crystals

Silver chlorobromide (AgClxBr1-x, 0 < x < 1) nanocubes with a highly uniform size, morphology, and crystallinity have been successfully synthesized through a co-precipitation of Ag+ ions with both Cl- and Br- ions in ethylene glycol containing polyvinyl pyrrolidone at mild temperatures. Compositions of the synthesized nanocubes can be easily tuned by controlling the molar ratio of Cl- to Br- ions in the reaction solutions. The size of the nanocubes is determined by varying a number of parameters including the molar ratio of Cl- to Br- ions, injection rate of Ag+ ions, and reaction temperature. The real-time formation of colloidal AgClxBr1-x nanocubes has been monitored, for the first time, by in situ highenergy synchrotron X-ray diffraction. The time-resolved results reveal that a fast injection rate of Ag+ ions is critical for the formation of AgClxBr1-x nanocubes with a highly pure face-centered cubic crystalline phase. The improved uniformity of the AgClxBr1-x nanocubes is beneficial for assembling them into order superlattices (e.g., photonic crystals) even by simply applying centrifugation forces. The stop band of the resulting photonic crystals can be easily tuned from the ultraviolet to the infrared region by using AgClxBr1-x nanocubes with different sizes. The variation of the dielectric constant of AgClxBr1-x associated with the change of the relative concentration of halide ions provides an additional knob to tune the optical properties of photonic crystals.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Developing radiation tolerant polymer nanocomposites using C 60 as an additive

In nuclear facilities utilizing plutonium, polymeric materials are subjected to long-term, close-contact, and continuous α radiation exposure, which can lead to compounding material degradation and eventual failure. Herein we model the attenuation of α particles by linear-low-density polyethylene (LLDPE), polyvinyl alcohol (PVA) thin films, and C 60 using Monte Carlo N-Particle Extended (MCNPX) software. The degradation of these materials was investigated experimentally by irradiating them with a beam of α particles of 5.8 MeV energy at a tandem Van de Graaff accelerator delivering a dose rate of 2.95 × 10 6 rad s –1 over a 7.1 mm 2 sample area. Our development of a method to test α particle-induced material degradation using a tandem accelerator is significant as degradation from naturally occurring α sources (i.e. Pu, Am) occurs too slowly for these sources to be used in practical experiments. Our results show that PVA nanocomposites containing 5 wt% C 60 were found to withstand about 7 times the α dose of undoped PVA films before a puncture in the film was detected. When these films were adhered to a LLDPE sheet the dual layer polymer was capable of withstanding about 13 times the dose of LLDPE and nearly twice the dose of the doped PVA thin film alone. Doping polymers with C 60 is an attractive way to generate more durable, radiation tolerant materials without increasing the thickness of the material which would lead to greater waste for disposal. Furthermore, the results herein help to resolve a prevalent technical challenge faced in nuclear facilities that utilize polymeric materials for nuclear processing and disposal.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Strain-induced alignment and phase behavior of blue phase liquid crystals confined to thin films

Here, we report on the influence of surface confinement on the phase behavior and strain-induced alignment of thin films of blue phase liquid crystals (BPs). Confining surfaces comprised of bare glass, dimethyloctadecyl [3-(trimethoxysilyl)propyl] ammonium chloride (DMOAP)-functionalized glass, or polyvinyl alcohol (PVA)-coated glass were used with or without mechanically rubbing to influence the azimuthal anchoring of the BPs. These experiments reveal that confinement can change the phase behavior of the BP films. For example, in experiments performed with rubbed-PVA surfaces, we measured the elastic strain of the BPs to change the isotropic–BPII phase boundary, suppressing formation of BPII for film thicknesses incommensurate with the BPII lattice. In addition, we observed strain-induced alignment of the BPs to exhibit a complex dependence on both the surface chemistry and azimuthal alignment of the BPs. For example, when using bare glass surfaces causing azimuthally degenerate and planar anchoring, BPI oriented with (110) planes of the unit cell parallel to the contacting surfaces for thicknesses below 3 μm but transitioned to an orientation with (200) planes aligned parallel to the contacting surfaces for thicknesses above 4 μm. In contrast, BPI aligned with (110) planes parallel to confining surfaces for all other thicknesses and surface treatments, including bare glass with uniform azimuthal alignment. Complementary simulations based on minimization of the total free energy (Landau–de Gennes formalism) confirmed a thickness-dependent reorientation due to strain of BPI unit cells within a window of surface anchoring energies and in the absence of uniform azimuthal alignment. In contrast to BPI, BPII did not exhibit thickness-dependent orientations but did exhibit orientations that were dependent on the surface chemistry, a result that was also captured in simulations by varying the anchoring energies. Overall, the results in this paper reveal that the orientations assumed by BPs in thin films reflect a complex interplay of surface interactions and elastic energies associated with strain of the BP lattice. The results also provide new principles and methods to control the structure and properties of BP thin films, which may find use in BP-templated material synthesis, and BP-based optical and electronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Control of formation of viscoelastic droplets and distribution of nano-inclusions in functional deposition for lithium–sulfur batteries

The electrospray process produces micro/nanodroplets for various applications such as thin and uniform coatings, drug carriers and mass spectrometry. In this paper, we study the spray processes of viscoelastic jets using simulations and experiments. In discretized modeling, the jet is perturbed with axisymmetric instability and the growth of this instability causes the jet to break into droplets. For the experiments, a solution of polyvinyl alcohol in water is sprayed and is visualized using a high-speed camera. The droplet size distribution is studied from simulations with experiments for three spray cases: electrospray, air spray, and air-controlled electrospray. Our simulations and experiments reveal that the electric field is effective in reducing the droplet size, while air flow offers more jet break-ups and thus a larger number of droplets. As a result, air-controlled electrospray where these two driving forces are synergistically combined leads to a larger number of smaller droplets than electrospray or air spray. As a result, we applied three spray processes to obtain a deposition of sulfur/mesoporous carbon/graphene/polymer binder composites as a lithium sulfur battery cathode and demonstrated that air-controlled electrospray leads to a higher capacity and rate capability than other processes, exhibiting 800 mA h g –1 at 0.5C and 600 mA h g –1 at 2C.

25 ENERGY STORAGE↗
DOE OSTI2019

Polypyrrole-encapsulated amorphous Bi 2 S 3 hollow sphere for long life sodium ion batteries and lithium–sulfur batteries

Sodium ion batteries (SIBs) and lithium–sulfur (Li–S) batteries are considered as the most enticing next-generation energy storage devices to displace the widely used lithium ion batteries due to their inherent advantages. In this work, polypyrrole-encapsulated amorphous Bi 2 S 3 hollow spheres are prepared by the sulfuration of Bi–glycol spheres with a polypyrrole (PPy) coating. Benefiting from the unique hollow structure (Kirkendall effect) and the excellent conductivity and flexibility of the PPy coating, this material can be applied in both SIBs and Li–S batteries. For SIBs, the unconductive amorphous Bi 2 S 3 is electrochemically reduced to conductive metallic Bi, leading to a Bi–PPy core–shell structure. The resulting Bi acts as the main active material while the PPy coating accommodates the volume variation of Bi during sodiation/desodiation. For Li–S batteries, the outer double layer structure effectively prevents the dissolution and “shuttle effect” of polysulfides by physically containing and chemically adsorbing polysulfides, and tolerates the volume expansion of sulfur. Meanwhile, the residual polyvinyl pyrrolidone in the preparation process is chemically bonded with sulfur and exhibits the electrochemical properties, and results in additional discharging/charging capacity. Hence, this multifunctional electrode shows excellent rate capability and cycling life in SIBs and Li–S batteries. This research allows new insight into the design of multifunctional electrodes.

25 ENERGY STORAGE↗
DOE OSTI2022

Catalytic production of tetrahydropyran (THP): a biomass-derived, economically competitive solvent with demonstrated use in plastic dissolution

Tetrahydropyran (THP) is a five-carbon heterocyclic ether that is non-carcinogenic, non-peroxide forming, biodegradable, and economically competitive with tetrahydrofuran (THF) as a solvent. In this work, THP has been synthesized from renewable biomass at >99.8% selectivity and 98% yield via hydrogenation of furfural-derived 3,4-dihydropyran (DHP) over Ni/SiO 2 in a continuous flow reactor at 150–200 °C. The apparent activation energy of THP formation is 31 kJ mol -1 , and the reaction orders with respect to the partial pressures of H 2 , DHP, and THP are: 2, 1, and -0.3. The kinetic data has been fitted to a Hougen–Watson model where the rate limiting step is the hydrogenation of adsorbed DHP. Ni/SiO 2 is shown to have a low deactivation rate constant of 0.012 h -1 over 100 h time on stream and can be regenerated in situ. As a performance advantage, THP is shown to be resistant to ring opening polymerization under strongly acidic conditions that THF is not, revealing it to be a superior solvent. Further, the minimum selling price of THP is competitive with the market price of THF ($$900 – 1400 per ton ) at a DHP feedstock cost of $1000 per ton. Conductor-like Screening Model for Real Solvents (COSMO-RS) and molecular dynamics (MD) simulations with 1008 solvents and 8 common plastics have demonstrated that THP can serve as an alternative solvent to THF, 2-methyltetrahydrofuran (MeTHF), and cyclopentyl methyl ether (CPME) for plastic dissolution, especially low-density polyethylene (LDPE), polypropylene (PP), polystyrene (PS) and polyvinyl chloride (PVC). This work establishes THP as a green solvent with excellent thermal, chemical and peroxidative stability that can be used for numerous applications, including waste plastic recycling.

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

Strong, thermo-reversible salogels with boronate ester bonds as thermal energy storage materials

Inorganic salt hydrates are promising phase change materials (PCMs) but suffer from low viscosity at temperatures above their melting point resulting in leakage problems during thermal storage applications. To achieve shape stabilization of one type of molten inorganic PCM – calcium nitrate tetrahydrate (CNH) – this work explored gelation of polyvinyl alcohol (PVA) in this solvent and the effect of dynamic boronate ester bonds on salogel strength. The occurrence of gelation of PVA in molten CNH but not in water is rationalized by the extremely high salt content and scarcity of hydration water in CNH, enabling intermolecular hydrogen bonding between PVA chains. While neat PVA salogels in CNH were weak, with a gel-to-sol transition temperature (T gel ) below room temperature, the addition of small amounts of borax (<~0.3 wt%) introduced dynamic covalent crosslinks and yielded salogels with T gel tunable over a wide temperature range from 7 to 70 °C. Here, the PVA/borax salogels were about one order of magnitude stronger than their well-known PVA/borax hydrogel counterparts, and, unlike PVA/borax hydrogels, were capable of retaining their shape and preventing leakage of molten CNH. Moreover, the salogels exhibited reversible and repeatable temperature-triggered gel-to-sol transitions and the ability to self-heal. The low polymer and crosslinker concentration also ensured that more than 95% of the heat of fusion of neat CNH was maintained in the salogels and was retained after twenty cycles of melting and crystallization, demonstrating the robust nature of these energy storage materials.

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

Orientation-controlled crystallization of γ-glycine films with enhanced piezoelectricity

Glycine, the simplest amino acid, is considered a promising functional biomaterial owing to its excellent biocompatibility and strong out-of-plane piezoelectricity. Practical applications require glycine films to be manufactured with their strong piezoelectric polar $\langle$001$\rangle$ direction aligned with the film thickness. Based on the recently-developed solidification approach of a polyvinyl alcohol (PVA) and glycine aqueous solution, in this work, we demonstrate that the crystal orientation of the as-synthesized film is determined by the orientation of glycine crystal nuclei. By controlling the local nucleation kinetics via surface curvature tuning, here we shifted the nucleation site from the edge to the middle of the liquid film, and thereby aligned the $\langle$001$\rangle$ direction vertically. As a result, the PVA–glycine–PVA sandwich film exhibits the highest average piezoelectric coefficient d 33 of 6.13 ± 1.13 pC N –1 . This work demonstrates a promising kinetic approach to achieve crystallization and property control in a scalable biocrystal manufacturing process.

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

Photocatalytic dechlorination of unactivated chlorocarbons including PVC using organolanthanide complexes

Simple lanthanide cyclopentadienyl (Cp) complexes can photochemically cleave the sp 3 carbon–chlorine bond of unactivated chlorinated hydrocarbons including polyvinyl chloride (PVC). Further, the excited state lifetimes of these simple complexes are among the longest observed for cerium complexes (175 ns for [(Cp Me4 ) 2 Ce(μ-Cl)] 2 ) and the light absorption by the Cp ligand is efficient, so photocatalytic reactivity is enhanced for cerium and now also made possible for neighboring, normally photoinactive, lanthanide congeners.

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

Hard carbon with an opened pore structure for enhanced sodium storage performance

The pore structure of hard carbon has a significant impact on its Na + storage capacity. Herein, a waste wood-derived hard carbon with opened pores (OP-HC) was fabricated with polyvinyl pyrrolidone (PVP) as an additive. Ex situ SAXS and HR-TEM testing results indicate that OP-HC with opened pores and enlarged d 002 interlayer spacing facilitates the reversible (de)sodiation of Na + ions. In situ TEM and XRD testing results demonstrate that OP-HC shows excellent structure stability during the (de)sodiation process. Thus, OP-HC delivers a high reversible charge capacity of 350.7 mA h g −1 at 0.05 C and an ultra-high initial Coulombic efficiency (ICE) of 94.9%. Moreover, OP-HC exhibits excellent cycling stability, and the assembled 18650 full cell with an OP-HC anode can achieve a high capacity retention of 94.5% after 400 cycles at 1.0 A. Furthermore, the excellent electrochemical performance and deep insights into OP-HC with opened pores and increased d 002 interlayer spacing offer a new strategy to design high-performance HC anodes for SIBs.

You, Shunzhang↗
DOE OSTI2026

Investigating PVC polymer–plasticizer interactions with atomistic MD simulations and potential of mean force calculations

For this work, atomistic molecular dynamics (MD) simulations coupled with potential of mean force (PMF) calculations were employed to investigate the interactions between PVC polymer chains containing 6–20 repeating units and various plasticizers, with the goal of identifying potential replacements for the toxic plasticizer di(2-ethylhexyl)phthalate (DEHP) used in blood bags. The selected plasticizers belong to various chemical families, such as orthophthalates, citrates, adipates, and the terephthalate DEHT. Both the polymer and the plasticizers lack ionizable groups, and their interactions are primarily governed by van der Waals and electrostatic forces. A model correlating PMF profiles with interaction forces was developed and validated across polyvinyl chloride (PVC) polymers of different lengths and all investigated plasticizers. This model provides insight into how structural variations in plasticizers influence their respective PMF values. The study ranks the investigated plasticizers based on binding affinity, identifying TOTM (tris(2-ethylhexyl) trimellitate, TEHTM), BTHC (butyryl trihexyl citrate, Citroflex B-6), ATHC (acetyl trihexyl citrate, Citroflex A-6, CA-6), and DEHT (bis(2-ethylhexyl)terephthalate, DOTP/DEHTP) as promising alternatives for further investigation. This comprehensive study encompasses PVC polymers of four different lengths and 14 plasticizers, with all data averaged over 30 independent simulations. The approach provides a deeper understanding of molecular interactions, enabling the tailoring of polymer–plasticizer systems for diverse applications, including extractables and leachables, with relevance spanning materials science to biomedical engineering, and also serves as a basis for developing coarse-grained simulation protocols. Overall, this study provides valuable insights for designing safer and more efficient plasticizer substitutes and is well supported by other studies.

Shet, Sai Athmeeya G. [Sri Sathya Sai Institute of↗
DOE OSTI2012

In-situ characterization of free-volume holes in polymer thin films under controlled humidity conditions with an atmospheric positron probe microanalyzer

A pulsed, slow positron beam, with a diameter of 200 {mu}m, was extracted into air through a thin SiN window of an atmospheric positron probe microanalyzer (PPMA), and used to measure the ortho-positronium lifetimes {tau} in polyvinyl alcohol and polycaprolactam sub-{mu}m-thick films. By measuring the variation of {tau} as a function of relative humidity, the effect of water molecules on the hole sizes, deduced from {tau}, was examined for the films with consideration to the chain mobility. The results demonstrate the usefulness of the atmospheric PPMA to the in-situ characterization of nanoscopic holes in thin films under practical conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Radiation tolerance of ultra-thin Formvar films

Mechanical behavior of free-standing polymer films with submicron thicknesses exposed to a radiation environment is poorly understood. Here, we study 110-nm-thin free-standing polyvinyl formal (Formvar) films irradiated at room temperature with 1-5 keV electrons or 3 MeV alpha particles. We measure mechanical properties and the elemental composition by spherical indentation and high-energy ion scattering, respectively. Results show that, with increasing radiation dose, the effective failure strain and film thickness decrease monotonically, while the dose dependence of the Young's modulus is non-monotonic. The failure strain and modulus scale with the average energy deposited in the film, while the film thickness exhibits a more complex behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2013

High carrier mobility of CoPc wires based field-effect transistors using bi-layer gate dielectric

Polyvinyl alcohol (PVA) and anodized Al{sub 2}O{sub 3} layers were used as bi-layer gate for the fabrication of cobalt phthalocyanine (CoPc) wire base field-effect transistors (OFETs). CoPc wires were grown on SiO{sub 2} surfaces by organic vapor phase deposition method. These devices exhibit a field-effect carrier mobility (μ{sub EF}) value of 1.11 cm{sup 2}/Vs. The high carrier mobility for CoPc molecules is attributed to the better capacitive coupling between the channel of CoPc wires and the gate through organic-inorganic dielectric layer. Our measurements also demonstrated the way to determine the thicknesses of the dielectric layers for a better process condition of OFETs.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Electrospinning of PVC with natural rubber

Polyvinyl chloride (PVC) was mixed with natural rubbers which are liquid natural rubber (LNR), liquid epoxidised natural rubber (LENR) and liquid epoxidised natural rubber acrylate (LENRA) for a preparation of a fine non-woven fiber’s mat. PVC and each natural rubbers(PVC:LENR, PVC:LNR and PVC:LENRA) were mixed based on ratio of 70:30. Electrospinning method was used to prepare the fiber. The results show that the spinnable concentration of PVC/ natural rubber/THF solution is 16 wt%. The morphology, diameter, structure and degradation temperature of electrospun fibers were investigated by scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). SEM photos showed that the morphology and diameter of the fibers were mainly affected by the addition of natural rubber. TGA results suggested that PVC electrospun fiber has higher degradation temperature than those electrospun fibers that contain natural rubber.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Surface plasmon coupled emission studies on engineered thin film hybrids of nano α−Al{sub 2}O{sub 3} on silver

We report the first time engineering and fabrication of a novel thin film hybrid of nano α-alumina doped in a polyvinyl alcohol (PVA) matrix along with rhodamine b (Rh.B) on a silver thin film. Silver films of 50 nm thickness on glass slides were fabricated by thermal evaporation. Nano α-alumina was synthesized through the combustion route and characterized by XRD. The α-alumina was dispersed in the PVA-Rh.B matrix by tip sonication. The resultant solution was spin coated on the Ag thin film at 3000 rpm to generate an overcoat of ∼30 nm. We have designed and constructed an opto-mechanical setup for performing the SPCE studies. Excitation with a 532 nm continuous laser, led to the coupling of the energy of Rh.B emission to the surface plasmon modes of silver. The emission @ 580 nm was recorded using an Ocean Optics(copyright, serif) fiber optic spectrometer. Calculation of the ratio of signal intensity between the directional SPCE and isotropic fluorescence gives us the factor of signal enhancements which SPCE offers. We report an '8 fold' signal enhancement attributed to SPCE arising from the metal oxide doped thin film hybrid. We observed only a '5 fold' signal enhancement in the case of a thin film hybrid without α-alumina. The emission was also 92% P-polarized which is in coherence with the theory of SPCE. The greater degree of signal enhancement observed in the α-alumina doped thin film substrate can be attributed to the surface roughness which alumina offers to silver, which along with the porous nature of alumina enables a greater degree of adsorption of Rh.B which results in a higher emission intensity. Computational modeling was also performed, based on surface plasmon resonance (SPR) calculations to provide theoretical background to observed experimental data. The α-alumina thin film hybrid can be extended as an economical sensing platform towards the high sensitive detection of analytes.

36 MATERIALS SCIENCE↗
DOE OSTI2014

The feasibility of using methylene blue sensitized polyvinylalcohol film as a linear polarizer

Linear light polarizing films selectively transmit radiations vibrating along an electromagnetic radiation vector and selectively absorb radiations vibrating along a second electromagnetic radiation vector. It happens according to the anisotropy of the film . In the present study the polarization effects of methylene blue sensitized polyvinyl alcohol is investigated. The polarization effects on the dye concentration, heating and stretching of film also are evaluated.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Surface plasmon enhanced third-order optical nonlinearity of Ag nanocomposite film

We obtain a large third-order optical nonlinearity (χ{sup (3)} ≈ 10{sup −10}esu) of silver nanoparticles dispersed in polyvinyl alcohol/tetraethyl orthosilicate matrix using single beam z-scan technique at 532 nm by Q-switched Nd:YAG laser. We have shown that mechanisms responsible for third-order optical nonlinearity of Ag nanocomposite film are reverse saturable absorption (RSA) and self-defocusing in the purlieu of surface plasmon resonance (SPR). Optical band-gap and width of SPR band of Ag nanocomposite film decrease with increasing silver concentration, which leads to enhancement of local electric field and hence third-order optical nonlinearity. Optical limiting, due to RSA has also been demonstrated at 532 nm.

77 NANOSCIENCE AND NANOTECHNOLOGY↗