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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Ionic complexation of endblock-sulfonated thermoplastic elastomers and their physical gels for improved thermomechanical performance

Thermoplastic elastomers (TPEs) composed of nonpolar triblock copolymers constitute a broadly important class of (re)processable network-forming macromolecules employed in ubiquitous commercial applications. Physical gelation of these materials in the presence of a low-volatility oil that is midblock-selective yields tunably soft TPE gels (TPEGs) that are suitable for emergent technologies ranging from electroactive, phase-change and shape-memory responsive media to patternable soft substrates for flexible electronics and microfluidics. Many of the high-volume TPEs used for these purposes possess styrenic endblocks that are inherently limited by a relatively low glass transition temperature. To mitigate this shortcoming, we sulfonate and subsequently complex (and physically crosslink) the endblocks with trivalent Al3+ ions. Doing so reduces the effective hydrophilicity of the sulfonated endblocks, as evidenced by water uptake measurements, while concurrently enhancing the thermomechanical stability of the corresponding TPEGs. Chemical modification results, as well as morphological and property development, are investigated as functions of the degree of sulfonation, complexation and TPEG composition. (C) 2020 Published by Elsevier Inc.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Tailored PEDOT:PSS hole transport layer for higher performance in perovskite solar cells: Enhancement of electrical and optical properties with improved morphology

Precise control over the charge carrier dynamics throughout the device can result in outstanding performance of perovskite solar cells (PSCs). Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is the most actively studied hole transport material in p-i-n structured PSCs. However, charge transport in the PEDOT:PSS is limited and inefficient because of its low conductivity with the presence of the weak ionic conductor PSS. In addition, morphology of the underlying PEDOT:PSS layer in PSCs plays a crucial role in determining the optoelectronic quality of the active perovskite absorber layer. This work is focused on realization of a non-wetting conductive surface of hole transport layer suitable for the growth of larger perovskite crystalline domains. This is accomplished by employing a facile solvent-engineered (ethylene glycol and methanol) approach resulting in removal of the predominant PSS in PEDOT:PSS. The consequence of acquiring larger perovskite crystalline domains was observed in the charge carrier dynamics studies, with the achievement of higher charge carrier lifetime, lower charge transport time and lower transfer impedance in the solvent-engineered PEDOT:PSS-based PSCs. Use of this solvent-engineered treatment for the fabrication of MAPbI3 PSCs greatly increased the device stability witnessing a power conversion efficiency of 18.18%, which corresponds to ~37% improvement compared to the untreated PEDOT:PSS based devices.

14 SOLAR ENERGY↗
DOE OSTI2025

Fast-rate joining of thermoplastic composites using integrated additive manufacturing and compression molding process

The integration of additive manufacturing (AM) technology with compression molding (CM), has emerged as a high-performance composite manufacturing technology in recent years. In the AM-CM process, quickly deposited AM preform on a mold undergoes a rapid compaction cycle to fabricate structurally robust composite parts due to highly controlled fiber alignment (from AM) and reduced porosity (from CM). Currently, AMCM-based part size is limited by the size of the mold volume, thus posing a challenge to manufacture scalable parts. Here, this work focuses on joining techniques developed to enable fast rate joining of short fiber-reinforced thermoplastic composite parts using the AM-CM process. Acrylonitrile butadiene styrene resin reinforced with 20 wt% short carbon fiber composites was printed onto a flat mold and pressed under a hydraulic press. Fabricated panels were joined by the (a) mechanical impression at the joining interface and (b) over-molded continuous carbon fiber (CCF) sheet. Tensile tests were performed to characterize the joining strength of both mechanical impression-based joints and CCF over molded joints. Among the mechanical impression-based joints, a U-shape channel allowed the fibers to flow between two joint parts, and 280 % increased mechanical properties were observed. The continuous carbon fiber-based over molded joint CCF showed 350 % increase in tensile strength compared to the butt joints.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Effect of overcharge on Li(Ni 0.5 Mn 0.3 Co 0.2 )O 2 /Graphite cells–effect of binder

Cells based on NMC/graphite, containing styrene-butadiene rubber/carboxymethylcellulose binder in the anodes and pVdF latex/carboxymethykellulose in the cathodes, were systematically overcharged to 100, 120, 140, 160, 180, 250% and 270% state-of-charge. The impact of the binder was characterized by elemental analysis, SEM, and HPLC. These results were compared to similar cells just using the poly (vinylidene difluoride) binder. Not only did the binder impact the rate of transition metal transport from the cathode to the anode, it also had a marked effect on the microstructure and composition of the materials on the anode surface.

25 ENERGY STORAGE↗
DOE OSTI2020

Effect of binder on the overcharge response in LiFePO 4 -containing cells

Two types of small pouch cells based on LiFePO 4 /graphite, one containing a N-methyl pyrrolidinone (NMP)-soluble binder, poly(vinylidene difluoride), and the other an aqueous-soluble binder, styrene-butadiene rubber/carboxymethylcellulose were systematically charged to 100, 120, 140, 160, 180, and 250% state of charge (SOC). The cells were then discharged to 3.0 V at room temperature before being disassembled for postmortem analysis. Microstructural changes in the anode associated with increasing SOC were more pronounced in the aqueous processed cells in comparison to the NMP-processed cells. Dendrite formation was observed on the aqueous-processed anode at 120% SOC, while the NMP-processed anode surface does not show dendrites until 250% SOC. Overall, the aqueous-processed anode surfaces displayed more evidence of microstructural degradation as a function of increasing SOC. In the NMP-processed cells, four organic compounds on the anode surface were found to show a dependence on SOC, while only two displayed a similar dependency in the aqueous-processed cells. The nature of the binder changed the number and composition of the species found at the anode.

25 ENERGY STORAGE↗
DOE OSTI2025

Property optimized energy absorber for automotive bumpers utilizing multi-material and structural design strategies

This study proposes a novel design for automotive bumper using optimized lattice structures and multi-materials to balance low-speed collision and high-speed pedestrian impact performance. Different blends of 20 % carbon fiber-reinforced acrylonitrile butadiene styrene with thermoplastic polyurethane were used to tailor material properties. The energy absorber features lattice structures with customized mechanical responses, created by varying the incline angle θ from 0 to 180°. We conducted 576 finite element simulations on a half-scale model to optimize energy absorption and stiffness, leading to 66 optimized designs that met both low-speed and high-speed impact criteria. Two sub-scale optimized energy absorbers with different peak forces—both meeting low-speed impact requirements—were 3D printed and validated through drop-weight testing. The one with lower peak stress demonstrated a more compliant response, exhibiting approximately 90 % lower initial peak force and an increase in energy absorption of around 33 % (from 24 J to 32 J). Compared to the baseline triangular lattice, the optimized absorber increased energy absorption by 68 % from (19 J to 32 J) and reduced peak stress by 70 %. It also showed near-complete recovery with minimal fractures, making it suitable for repeated use. This design improves safety while offering a lightweight, durable, and cost-effective bumper system.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Effects of surface treatments on ABS mechanical properties from fused filament fabrication

This paper examines the influence of surface treatments on the mechanical properties of acrylonitrile butadiene styrene (ABS) samples printed by fused filament fabrication (FFF). Prior efforts have applied brushing, painting, solvent dipping, infiltration, and vapor smoothing as post-processing surface treatments to improve the mechanical properties of FFF components. Additionally, because FFF can produce components with undesirable surface roughness, mechanical abrasion, epoxy coating, and acetone treatment may increase tensile strength by decreasing stress concentrations. Ridged surface texture may provide desirable tribological or handling properties. Based on these opportunities, this paper investigates abrasive media blasting, epoxy coating, acetone immersion, and ridged texturing surface treatments on the tensile strength and other mechanical properties of FFF ABS samples. ASTM D638-14 Type-I samples were printed, treated on all sample sides, and tested. From tensile tests, the elastic modulus, tensile strength, and fracture strain for both the untreated and treated ABS samples were calculated. For each sample, the surface finish and fracture macromorphology were observed with optical microscopy and the roughness values for the surface finish were calculated from profilometer data. Furthermore, samples were submerged in water and weighed periodically to measure mass changes due to water absorption. From surface profilometry and optical miscopy data, mechanical media blasting, epoxy coating, and immersion in all concentrations of acetone decreased surface roughness. Overall, on average, grit blasting with large beads and epoxy coating led to 2.6% and 1.2% increases in tensile strength, respectively; immersion in 40% acetone led to a 1.9% increase in tensile strength while treatment in 60% and 80% acetone decreased tensile strength by 4.9% and 1.9%, respectively. The study concludes that only grit blasting with large beads, immersion in 60% acetone, and the ridged texture significantly affected the tensile strength.

36 MATERIALS SCIENCE↗
DOE OSTI2023

On electron beam-induced degradation of vinyl ester thermosets

We have demonstrated that electron beam radiolysis induces scissions of the C-O-C bonds along the backbone of the chains of unsaturated polyester thermosets of different compositions based on dicyclopentadiene, isophthalic acid, epoxy vinyl ester, and terephthalic acid. The radiolysis is imminent irrespective of the degree of crosslinking in the thermosets both in neat resins and in the presence of solvents. Electron Paramagnetic Resonance (EPR) results show the formation of the alkoxyl radicals and C-centered radicals as the primary intermediate products of the C-O-C scissions. While the alkoxyl radicals of these resins exhibit very good stability even six months after the irradiation, the C-centered radicals decay very rapidly via their reactions with oxygen that is available either as adsorbed in the resins, dissolved in solvents or from the environment. The radiolytically produced •OH radicals in the unsaturated-ester aqueous solutions play a major role in inducing scissions on the backbone of the polymer chains. The solvated electrons (e s ) from organic solvents, such as dimethyl sulfoxide and isopropyl alcohol, also induce direct scission of the C-O-C bonds, giving rise to the formation of alkoxyl radicals and C-centered radicals. However, a considerable fraction of es is scavenged by the dissolved O 2 to produce O 2 - . Despite the radiation-induced scissions, irradiation of the resins at a dose level of 1000 kGy results in an increase of the glass transition temperature, Tg. This is due to the simultaneous radiation-induced polymerization of the vinyl monomers, toluene, and styrene that are present in the resins. The increase in Tg is observed in all the resins except for the terephthalic polyester resin in aqueous solution, in which the absence of these monomers results in Tg decreasing sharply with irradiation. This work demonstrates that ionizing radiation triggers continuous free radical-chain reactions that lead to the formation of recyclable oligomers.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2023

Experimental and computational study of polystyrene sulfonate breakdown by a Fenton reaction

Experimental studies and ab initio quantum chemistry calculations were combined to investigate the process by which a Fenton reaction breaks down polystyrene sulfonate. The experimental results show that both molecular weight reduction and loss of aromaticity occur nearly simultaneously, a finding that is supported by the calculations. The results show that more than half of the material is broken down to low molecular weight compounds (< 500 g/mol) with two molar equivalents of H 2 O 2 per styrene monomer. The calculations provide insights into the reaction pathways and indicate that at least two hydroxyl radicals are required to cleave backbone Csingle bondC bonds or to eliminate aromaticity. The calculations also show that, of the aromatic carbons, hydroxyl radical is most likely to add to the carbon bonded to sulfur. This finding explains the loss of hydrogen sulfite anion early in the process and also the efficient reduction of Fe(III) to Fe(II) through semiquinone formation. Taken together the experimental and computational results indicate that the reaction is very efficient and that very little H 2 O 2 is lost to unproductive reactions. In conclusion, this high efficiency is attributed to the close association of Fe atoms with the sulfonate group such that hydroxyl radicals are generated near the polymer chains.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Connecting radiation-driven changes in structural, thermal, and mechanical properties in several medical device polymers

Stemming from security threats and shortages in supply, a recent push has emerged to develop alternatives to radioisotope Cobalt-60 gamma radiation for sterilization of polymeric medical products, including electron beam (e-beam) and X-ray machine-based sources. However, before large-scale implementation, the effects of these non-isotope-based methods must be thoroughly investigated from several perspectives, involving their potential detrimental effects on the structural, thermal, and mechanical properties of polymers in medical devices. This paper investigates such effects in commonly used medical device polymers, including polypropylene homopolymer (PPH), polyolefin elastomer (POE), low-density polyethylene (LDPE), acrylonitrile butadiene styrene (ABS), and chlorobutyl rubber (CIIR). To connect radiation-driven changes in polymer structural and thermal properties and corresponding changes in mechanical properties, several characterization techniques were utilized, including gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). We found that the tensile strength of X-ray irradiated PPH, as well as X-ray, e-beam, and gamma irradiated CIIR decreases due to chain scission, which is corroborated by GPC and DMA. The GPC results of LDPE suggest chain scission, but interestingly without a corresponding decline in tensile strength. By comparison, POE and ABS appear to undergo further crosslinking with increasing irradiation dose, which generally strengthens them. Importantly, in the vast majority of the cases, there were small to no changes in properties upon changing radiation technologies (at a given dose), i.e., no radiation source dependence. However, in a few specific cases, radiation method dependencies did arise, for instance, in terms of the molecular weight of PPH being significantly increased upon X-ray irradiation, while the melting temperature, glass transition temperature, and elongation at break reduced compared to gamma. Overall, this study provides valuable insight into radiation-driven chemical and structural changes in polymers that produce changes in physical and functional properties.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Dispersion of modified fumed silica in elastomeric nanocomposites

In polymer nanocomposites, surface modification of silica aggregates can shield Coulombic interactions that inhibit agglomeration and formation of a network of agglomerates. Surface modification is usually achieved with silane coupling agents although carbon-coating during pyrolytic silica production is also possible. Pyrogenic silica with varying surface carbon contents were dispersed in styrene-butadiene (SBR) rubber to explore the impact on hierarchical dispersion, the emergence of meso-scale structures, and the rheological response. Pristine pyrogenic silica aggregates at concentrations above a critical value (related to the Debye screening length) display correlated meso-scale structures and poor filler network formation in rubber nanocomposites due to the presence of silanol groups on the surface. Here, in the present study, flame synthesized silica with sufficient surface carbon monolayers can mitigate the charge repulsion thereby impacting network structural emergence. The impact of the surface carbon on the van der Waals enthalpic attraction, a * , is determined. The van der Waals model for polymer nanocomposites is drawn through an analogy between thermal energy, k B T, and the accumulated strain, γ. The rheological response of the emergent meso-scale structures depends on the surface density of both carbon and silanol groups.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Life cycle cost, energy, and carbon emissions of molds for precast concrete: Exploring the impacts of material choices and additive manufacturing

Molds for precast concrete are commonly used to create simple- to complex-shaped concrete products away from construction sites. These molds are often handmade from wood; however, additively manufacturing (AM, or 3D printing) fiber-reinforced polymer composites is an advantageous alternative, producing significantly more durable, highly complex molds faster, but likely at a higher cost. Here, this study explores the impact of material and production variables on the cost, energy, and carbon emissions of employing composite AM molds over the full lifecycle. The case study employed techno-economic and life cycle assessments to show that using wood flour–poly(lactic acid) or recycled carbon fiber–acrylonitrile butadiene styrene for AM molds can be less expensive than conventional wood molds, especially when considering use phase costs. While wood molds have the least environmental impacts due to wood's higher biogenic carbon sequestration and minimal processing, optimizing AM designs could reduce energy demand, carbon emissions, and cost.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Trace explosives sampling for security applications (TESSA) study: Evaluation of procedures and methodology for contact sampling efficiency

We report the detection of trace amounts of explosive materials is critical to the security at mass transit centers (e.g., airports and railway stations). In a typical screening process, a trap is used to probe a surface of interest to collect and transfer particulate residue to a detector for analysis. The collection of residues from the surface being probed is widely viewed as the limiting step in this process. A multi-institutional study was performed to establish a methodology for the evaluation of sampling media collection efficiencies. Dry deposited residues of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), C-4 (an RDX-based explosive), and pentaerythritol tetranitrate (PETN) were harvested from acrylonitrile butadiene styrene (ABS) plastic, ballistic nylon (NYL), and uncoated aluminum surfaces using muslin, Texwipe cotton, and stainless-steel mesh traps. Transfer and collection efficiencies of the sample media were calculated based on liquid chromatography-mass spectrometry analysis. Dry transfer efficiencies (DTE%) to all tested surfaces were greater than 75%, with transfer to ABS plastic being the lowest. Collection efficiency (CE%) varied significantly across the traps and the surfaces, yet some conclusions can be drawn; nylon had the lowest CE% for all cases (~10%), and the stainless steel mesh had the lowest CE% for the evaluated traps (~20%). Though the testing parameters have been standardized among the participants to establish a framework for an independent comparison of contact sampling media and surfaces, substantial variations in the DTE% and the CE% were observed, suggesting that other variables can affect contact sampling.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Effects of particle inclusions on cracking in ultrathin barrier films

Here, the effects of particle inclusions with different mechanical properties on the development of cracks in ultra-thin barrier films have been studied. Two types of particles, alumina and poly(styrene-b-methyl methacrylate) with large differences in their elastic modulus were used, representing both hard and soft inclusions. Particles were seeded onto polyethylene naphthalate substrates and subsequently coated with atomic layer deposited Al 2 O 3 as a barrier film. Ca corrosion tests used to determine the performance of the barrier films revealed that soft polymer particle inclusions severely affect the development of cracking in barrier films as compared to stiff ceramic particles. Tensile tests also confirmed that the barrier films with polymer particle inclusions have the lowest value of critical onset strain. Parametric simulations, conducted by varying the elastic modulus of the particle inclusions over a wide range, resulted in a larger strain energy release rate near particle inclusions which promotes crack formation and negatively impacts the performance of barrier films with softer particle inclusions. Thus, the combination of high residual stresses in the barrier films with the presence of soft particle inclusions is found the most detrimental for the development of high-performance ultrathin barrier films.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Postsynthetic Oxidation of the Coordination Site in a Heterometallic Metal-Organic Framework: Tuning Catalytic Behaviors

Postsynthetic modification (PSM) in metal-organic frameworks (MOFs) can introduce multiple functionalities and alter the structural function for the desired application. However, the PSM of the coordination site faces the challenges of structural collapse or incompatibility between the original metal site and the newly formed coordination group. Herein, we developed a novel concept of introducing “primary” and “secondary” nodes, coexisting in a water-stable, Zr-based heterometallic MOF, [Zr6(µ3-OH)8(OH)8][CuI4(L1)4]2 (1-SH-a, H2L1 = 6-mercaptopyridine-3-carboxylic acid). The post-synthetic oxidation at the coordination site was successfully achieved in the “secondary” nodes [CuI4(L1)4]4-, while the robust “primary” nodes [Zr6(µ3-OH)8(OH)8]8+ stabilized the whole framework to form [Zr6(µ3-OH)8(OH)8][(CuI0.44CuII0.56(OH)0.56)4(L2)4]2 (1-SO3H, H2L2 = 6-sulfonicotinic acid). PSM of 1-SH-a to form 1-SO3H dramatically tuned the catalytic properties toward the styrene oxide ring-opening reaction to give a regioselectivity of primary alcohol (A) of ~99% compared with 1-SH-a (~71%).

Han, Yi↗
DOE OSTI2020

Resolving Triblock Terpolymer Morphologies by Vapor-Phase Infiltration

The spontaneous formation of well-organized three-dimensional (3D) nanostructures from self-assembled block copolymers (BCPs) holds promise for nanofabrication and lithography. The addition of a third block to BCPs provides access to a plethora of 3D geometries, but it remains difficult to resolve the geometry of such “three-color” structures when there is low contrast between the polymeric components at length scales of a few nm. Here, we apply vapor-phase infiltration synthesis to a silicon-containing triblock terpolymer, poly(1,1- dimethyl silacyclobutane-b-styrene-b-lactide) (PDMSB-b-PS-b-PLA or DSL) to distinguish the 3D microdomain morphologies of the two organic blocks, PLA and PS. Selective infiltration of ZnO within the PLA microdomains reveals morphologies consisting of three-color lamellae or lamellae combined with vertically aligned core-shell cylinders, depending on the volume fractions of each block. The infiltration produces ZnO nanoparticles throughout the 260 nm thickness of the DSL film, generating 3D nanocomposites containing ZnO and SiO x . These results provide a strategy for synthesizing multicomponent 3D nanostructures as well as visualizing the phase behavior of multi-block copolymers.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Compatibility of Fuel System Elastomers and Plastics with a Fast-Pyrolysis Oil (Bio-oil) at Room Temperature

Herein the compatibility of a fast-pyrolysis bio-oil with 17 elastomer and 21 plastic materials common to fuel storage, dispensing, and delivery systems was assessed by measuring volume and hardness. Diesel was used as the baseline for comparison. The elastomer and plastic specimens were exposed to the test fuels at 23 °C. The exposure times were 4 and 16 weeks for the elastomers and plastics, respectively. The elastomers (except for silicone and styrene butadiene) exhibited pronounced swelling in the bio-oil. This was especially true for the fluorocarbons and acrylonitrile rubbers. For the elastomers, a strong correlation between polarity and volume swell was observed. Compositional and structural analysis on one of the fluorocarbon materials showed that the bio-oil was less effective at extracting phthalate additives than the diesel. However, the crystallinity of a fluorocarbon was altered by the bio-oil. Unlike the elastomers, the plastic materials were less impacted by exposure to the bio-oil. This finding is attributed to their denser and more rigid molecular structures (compared to the elastomers). Notable swelling did occur in the nylons, but this swelling was attributed to water absorption rather than polarity. Comparison with previous studies showed that the observed swelling was lower for both the elastomers and the plastics. Solubility (and hence swell) increases with temperature, and because this study was conducted at 23 °C rather than 50 °C, the reduced temperature is responsible for the lower swell levels.

09 BIOMASS FUELS↗
DOE OSTI2020

Mathematical Modeling of Liquid-Phase Alkylation of Benzene with Ethylene Considering the Process Unsteadiness

Ethylbenzene is a key intermediate in the manufacture of styrene that is an important industrial monomer. Ethylbenzene is produced by benzene alkylation using either gas-phase or liquid-phase methods. The liquid-phase alkylation that uses liquid acidic catalysts needs to be improved. We develop a mathematical model for the liquid-phase benzene alkylation. The reaction scheme, designed with a due analysis of desired and side reactions, and with the analysis of the formation of deactivating agents, reflects, in particular, the influence of the concentration of heavy hydrocarbons on the catalyst activity. The account of the catalyst deactivation by heavy alkylaromatics allows predictions of the temporal changes in the outputs of the alkylation process. In particular, the decrease of the ethylbenzene concentration by 2–3 wt % and increase of the polyalkylate outlet concentration by 1.5–2 wt % are the results of the catalyst deactivation. These effects, however, can be compensated by 1.3-time increase of polyalkylate supply and by the temperature increase up to 398 K. Finally, the calculations also show that it is possible to decrease the supply of fresh catalyst from 0.498 to 0.472 t/hour without loss in the yield of ethylbenzene.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗