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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Functional Biomimetic Polymers with Antimicrobial Activity

At PNNL, we have developed a completely new class of synthetic biomimetic sequence-defined polymers based on triazine chemistry, which we call TZPs. PNNL's new polymers offer the opportunity to achieve similar functions to natural macromolecules; specifically we designed and synthesized a diversity of test molecules for antimicrobial activity. Antimicrobial activity against a variety of wild type and drug resistant pathogens was found.

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

Solution-Deposited and Patternable Conductive Polymer Thin-Film Electrodes for Microbial Bioelectronics

Microbial bioelectronic devices integrate naturally occurring or synthetically engineered electroactive microbes with microelectronics. These devices have a broad range of potential applications, but engineering the biotic–abiotic interface for biocompatibility, adhesion, electron transfer, and maximum surface area remains a challenge. Prior approaches to interface modification lack simple processability, the ability to pattern the materials, and/or a significant enhancement in currents. We report a novel conductive polymer coating that significantly enhances current densities relative to unmodified electrodes in microbial bioelectronics is reported. The coating is based on a blend of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) crosslinked with poly(2-hydroxyethylacrylate) (PHEA) along with a thin polydopamine (PDA) layer for adhesion to an underlying indium tin oxide (ITO) electrode. When used as an interface layer with the current-producing bacterium Shewanella oneidensis MR-1, this material produces a 178-fold increase in the current density compared to unmodified electrodes, a current gain that is higher than previously reported thin-film 2D coatings and 3D conductive polymer coatings. The chemistry, morphology, and electronic properties of the coatings are characterized and the implementation of these coated electrodes for use in microbial fuel cells, multiplexed bioelectronic devices, and organic electrochemical transistor based microbial sensors are demonstrated. It is envisioned that this simple coating will advance the development of microbial bioelectronic devices.

patterned bioelectronics↗
DOE OSTI2020

Effects of Ion Size and Dielectric Constant on Ion Transport and Transference Number in Polymer Electrolytes

Salt-doped polymers without added solvents have potential as nonflammable, robust electrolytes for batteries but suffer from low ion conductivity. Using bulky anions with delocalized charge may reduce ion agglomeration and increase conduction. However, size asymmetry between ions may increase preferential solvation of cations versus the larger anions, lowering the transference number t + (fraction of conductivity contributed by the cation, relevant to battery performance). We use coarse-grained molecular dynamics simulations, including a 1/r 4 potential to capture size-dependent solvation effects, to relate polymer and ion chemistry to t + and overall conductivity. At low ion size disparity, increasing dielectric constant improves cation conduction due to the mitigation of ion aggregation and correlated cation-anion motion. However, at high ion size disparity, high dielectric medium results in strong preferential solvation of cations, reducing cation mobility and t + . The trade-off between better cation-anion separation and cation preferential solvation suggests that the strategy of developing high dielectric polymers may enhance performance only at low ion size disparity.

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

Mapping the Interfacial Chemistry and Structure of Partially Fluorinated Bottlebrush Polymers and Their Linear Analogues

Polymer interfaces are key to a range of applications including membranes for chemical separations, hydrophobic coatings, and passivating layers for antifouling. While important, challenges remain in probing the interfacial monolayer where the molecular ordering and orientation can change depending on the chemical makeup or processing conditions. In this work, we leverage surface specific vibrational sum frequency generation (SFG) and the associated dependence on molecular symmetry to elucidate the ordering and orientations of key functional groups for poly(2,2,2-trifluoroethyl methacrylate) bottlebrush polymers and their linear polymer analogues. These measurements were framed by atomistic molecular dynamic simulations to provide a complementary physical picture of the gas–polymer interface. Simulations and SFG measurements show that methacrylate backbones are buried beneath a layer of trifluoroethyl containing side groups that result in structurally similar interfaces regardless of the polymer molecular weight or architecture. The average orientational angles of the trifluoroethyl containing side groups differ depending on polymer linear and bottlebrush architectures, suggesting that the surface groups can reorient via available rotational degrees of freedom. Results show that the surfaces of the bottlebrush and linear polymer samples do not strongly depend on molecular weight or architecture. As such, one cannot rely on increasing the molecular weight or altering the architecture to tune surface properties. This insight into the polymer interfacial structure is expected to advance the design of new material interfaces with tailored chemical/functional properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Tailoring renewable materials via plant biotechnology

Plants inherently display a rich diversity in cell wall chemistry, as they synthesize an array of polysaccharides along with lignin, a polyphenolic that can vary dramatically in subunit composition and interunit linkage complexity. These same cell wall chemical constituents play essential roles in our society, having been isolated by a variety of evolving industrial processes and employed in the production of an array of commodity products to which humans are reliant. However, these polymers are inherently synthesized and intricately packaged into complex structures that facilitate plant survival and adaptation to local biogeoclimatic regions and stresses, not for ease of deconstruction and commercial product development. Herein, we describe evolving techniques and strategies for altering the metabolic pathways related to plant cell wall biosynthesis, and highlight the resulting impact on chemistry, architecture, and polymer interactions. Furthermore, this review illustrates how these unique targeted cell wall modifications could significantly extend the number, diversity, and value of products generated in existing and emerging biorefineries. These modifications can further target the ability for processing of engineered wood into advanced high performance materials. In doing so, we attempt to illuminate the complex connection on how polymer chemistry and structure can be tailored to advance renewable material applications, using all the chemical constituents of plant-derived biopolymers, including pectins, hemicelluloses, cellulose, and lignins.

09 BIOMASS FUELS↗
DOE OSTI2025

Random heteropolymers as enzyme mimics

Despite successes in replicating the primary–secondary–tertiary structure hierarchy of protein, it remains elusive to synthetically materialize protein functions that are deeply rooted in their chemical, structural and dynamic heterogeneities. We propose that for polymers with backbone chemistries different from that of proteins, programming spatial and temporal projections of sidechains at the segmental level can be effective in replicating protein behaviours; and leveraging the rotational freedom of polymer can mitigate deficiencies in monomeric sequence specificity and achieve behaviour uniformity at the ensemble level. Here, guided by the active site analysis of about 1,300 metalloproteins, we design random heteropolymers (RHPs) as enzyme mimics based on one-pot synthesis. We introduce key monomers as the equivalents of the functional residues of protein and statistically modulate the chemical characteristics of key monomer-containing segments, such as segmental hydrophobicity. The resultant RHPs form pseudo-active sites that provide key monomers with protein-like microenvironments, co-localize substrates with catalytic or cofactor-binding sidechains and catalyse reactions such as oxidation and cyclization of citronellal with isopulegol/menthoglycol selectivity. This RHP design led to enzyme-like materials that can retain catalytic activity under non-biological conditions, are compatible with scalable processing and have expanded substrate scope, including environmentally long-lasting antibiotic tetracycline.

36 MATERIALS SCIENCE↗
DOE OSTI2021

In Situ Polymerization of Polypyrrole and Polyaniline on the Surface of Magnetic Molybdenum Trioxide Nanoparticles: Implications for Water Treatment

Photocatalyst dissolution greatly diminishes the usability of photocatalysts in water treatments. Coating conductive polymers on the surface of photocatalysts can reduce dissolution without compromising the photocatalytic properties of the material. In this investigation, polypyrrole (PPy) and polyaniline (PANI) were used to coat two magnetic MoO 3 nanoparticles with different surface chemistries. The polymer-coated MoO 3 @Fe 3 O 4 nanoparticles were synthesized by optimizing the mole fractions of PPy or PANI, MoO 3 , and Fe 3 O 4 . The optimized PPy@ MoO 3 @Fe 3 O 4 (PMF1) and PANI@MoO 3 @Fe 3 O 4 (PMF2) resulted in 95.39 and 75.98% methylene blue dye removal, respectively. MoO 3 dissolutions of 4.12 and 5.6% were obtained for PMF1 and PMF2, respectively, demonstrating the reduced solubility of the coated nanoparticles as compared to their uncoated counterparts (7.87% for MF1 and 18.1% for MF2). In situ small-angle neutron scattering (SANS) was utilized to investigate the polymerization kinetics of PPy and PANI on nanoparticles. The results revealed that an increase in base material oxygen vacancies resulted in the reduction of both the polymer size and the polymerization rate. Furthermore, this study demonstrated that SANS provides valuable insights into the polymer growth mechanisms on nanoparticle surfaces.

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

Study of electron-induced chemical transformations in polymers

In extreme ultraviolet (EUV) photoresist exposure, the primary and secondary electrons drive chemistry rather than the EUV photons themselves. These electrons have a wide range of energies below approximately 80 eV, which are capable of complex network of reactions during exposure. To better understand the ability of electrons of different energies within the EUV primary and secondary electron range, we want to characterize and compare the chemistry induced in pure polymer films by direct exposure to electrons. Thin films of poly(tert-butyl methacrylate), poly(methyl methacrylate), and poly(4-hydroxystyrene) were exposed to a 20 to 80 eV electron beam. Outgassing during exposure was characterized in-situ using a quadrupole residual gas analyzer. The thickness changes were measured using ellipsometry and chemical bond structure data were collected using Fourier-transform infrared spectroscopy (FTIR) after exposure to compare different exposure conditions. Poly(4-hydroxystyrene) demonstrated stability during electron exposures. Exposures of the other two materials led to outgassing of protecting groups, the intensity of which decayed in time. Outgassing, FTIR, and thickness loss data exhibited approximately linear relationships to each other.

Mueller, Maximillian↗
NASA NTRS1997

Comparison of Oxygen Gauche Effects in Poly(Oxyethylene) and Poly(ethylene terephtylene) Based on Quantum Chemistry Calculations

The so-called oxygen gauche effect in poly(oxyethylene) (POE) and its model molecules such as 1,2-dimethoxyethane (DME) and diglyme (CH3OC2H4OC2H4OCH3) is manifested in the preference for gauche C-C bond conformations over trans. This has also been observed for poly(ethylene terephthalate) (PET). Our previous quantum chemistry calculations demonstrated that the large C-C gauche population in DME is due, in part, to a low-lying tg +/- g+ conformer that exhibits a substantial 1,5 CH ... O attraction. New calculations will be described that demonstrate the accuracy of the original quantum chemistry calculations. In addition, an extension of this work to model molecules for PET will be presented. It is seen that the C-C gauche preference is much stronger in 1,2 diacetoxyethane than in DME. In addition, there exist low-lying tg +/- g+/- and g+/-g+/-g+/- conformers that exhibit 1,5 CH ... O attractions involving the carbonyl oxygens. It is expected that the -O-C-C-O- torsional properties will be quite different in these two polymers. The quantum chemistry results are used to parameterize rotational isomeric states models (RIS) and force fields for molecular dynamics simulations of these polymers.

Jaffe, Richard↗
DOE OSTI2023

Moisture-driven CO 2 pump for direct air capture

Direct Air Capture, the chemical separation of carbon dioxide (CO 2 ) from air, is considered a necessary approach to generate negative carbon emissions and in turn limit global warming, though energetic and monetary costs must continue to decline to meet the needed gigaton scale. The promise of energy-efficient and continuous carbon dioxide membrane separation has only recently been investigated with the development of facilitated chemical transport and novel electrochemically driven methods. This work demonstrates the potential for continuous pumping of CO 2 from air using commercial anion exchange membranes driven solely by a water vapor gradient. A reactive transport model that couples ionic transport with moisture sensitive bicarbonate chemistry in charged polymers, also termed moisture swing sorption, was developed alongside experimentally measured equilibrium and transport properties of CO 2 and water vapor in Fumasep FAA-3 to determine the mass transport limits of such a system. The results show that the commercial membrane is kinetically limited by the moisture sensitive chemistry, enabling a CO 2 current of 1.1 μmol/m 2 • s. In diffusion limited materials, a CO 2 pumping flux can reach 11 μmol/m 2 • s in and peak performance is expected with a dry air relative humidity around 50% pumping into a saturated water vapor permeate. In all configurations, water loss becomes the major cost in such a separation and must be managed through optimal polymer design or water recovery mechanisms. The work demonstrates the applicability of a new driving force, the evaporation of water, to meet the energetic demand of CO 2 separation from air.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Atomic layer deposition of nanofilms on porous polymer substrates: Strategies for success

Atomic layer deposition (ALD) is a versatile technique for engineering the surfaces of porous polymers, imbuing the flexible, high-surface-area substrates with inorganic and hybrid material properties. Previously reported enhancements include fouling resistance, electrical conductance, thermal stability, photocatalytic activity, hydrophilicity, and oleophilicity. However, there are many poorly understood phenomena that introduce challenges in applying ALD to porous polymers. In this paper, we address five common challenges and ways to overcome them: (1) entrapped precursor, (2) embrittlement, (3) film fracture, (4) deformation, and (5) pore collapse. These challenges are often interrelated and can exacerbate one another. To investigate these phenomena, we applied various ALD chemistries to porous polymers including polyethersulfone, polysulfone, polyvinylidene fluoride, and polycarbonate track-etched membranes. Reaction-diffusion modeling revealed why certain precursors and processing conditions result in embrittling subsurface material growth, entrapment of unreacted precursors, and nongrowth. We quantify the limits of ALD processing temperatures that are dictated by thermal expansion mismatch and can lead to fractured ALD films. The results herein allow us to make recommendations to avoid, mitigate, or overcome the difficulties encountered when performing ALD and plasma-enhanced ALD on porous polymers. We intend this article to serve as a “lessons learned” guide informed by previous experience to provide a better understanding of the difficulties and limitations of ALD on porous polymers and knowledge-based guidelines for successful depositions. This knowledge can accelerate future research and help experimentalists navigate and troubleshoot as they expose porous polymers to reactive precursor vapors.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Polydiallylammonium-Polysulfone Multiblock Copolymers for Moisture-Swing Direct Air Capture of Carbon Dioxide

Polysulfones are an important class of materials for a variety of applications due to their excellent strength and thermal stability. Quaternary ammonium polymers are also useful materials due to their ion exchange properties, and such materials with alkaline counterions have been used to capture carbon dioxide (CO 2 ) from ambient air through a moisture-driven mechanism. Herein, we design sulfone-based multiblock copolymers containing ammonium functionalities and demonstrate their potential for CO 2 capture. Specifically, a series of multiblock copolymers containing both polydiallyldimethylammonium (PDADMA) and polysulfone (PSf) blocks were synthesized. PSf blocks provide mechanical integrity, while the PDADMA blocks enable the direct air capture of CO 2 . Multiblock copolymers were synthesized at high yield, and PDADMA(OH)-PSf copolymer films with good flexibility and strength were formed with IECs of 424 μmol/g (17 mol % PDADMA(OH)), 1407 μmol/g (44 mol % PDADMA(OH)), and 1726 μmol/g (50 mol % PDADMA(OH)). Thermogravimetric analysis was used to determine that all films are thermally stable up to 345 °C. Differential scanning calorimetry revealed that the 17 and 44 mol % functionalized PDADMA(OH)-PSf multiblock copolymers showed one T g at 185 °C and 50 mol % PDADMA(OH)-PSf polymer showed a T g at 183 °C and a second T g at 16 °C. Atomic force microscopy showed that the multiblock polymers exhibit disordered phase separation. Furthermore, the copolymer materials displayed moisture-swing direct air capture of CO 2 , opening up pathways to utilize polymer architecture and chemistry to tailor the properties of promising sorbents.

42 ENGINEERING↗
DOE OSTI2022

Crosslinked Anionic Exchange Membranes (Spring Quarter Report)

With ever growing climate concerns, studying and optimizing hydrogen gas electrolyzers and fuel cells are of high importance. Polymeric anionic exchange membranes (AEM) are attractive replacements to the industry standard proton exchange membranes (PEM) due to their lack of precious metal catalysts and acidic conditions. However, AEMs on the market have yet to preform comparatively to PEMs. To bring AEMs to a competitive level, crosslinking chemistry within the polymer membranes is being investigated to enhance mechanical properties and performance. For this quarter, electrochemical systems, important AEM properties and considerations, and some characterization methods will be reviewed.

08 HYDROGEN↗
DOE OSTI2021

Three-Dimensional Printable, Extremely Soft, Stretchable, and Reversible Elastomers from Molecular Architecture-Directed Assembly

3D printing elastomers enables the fabrication of many technologically important structures and devices such as tissue scaffolds, sensors, actuators, and soft robots. However, conventional 3D printable elastomers are intrinsically stiff; moreover, the process of printing often requires external mechanical support and/or post-treatment. In this work, we exploit the self-assembly of a responsive linear-bottlebrush-linear triblock copolymer to create stimuli-reversible, extremely soft, and stretchable elastomers and demonstrate their applicability as inks for in situ direct-write printing 3D structures without the aid of external mechanical support or post-treatment. By developing a procedure for controlled synthesis of such architecturally designed block copolymers, we create elastomers with extensibility up to 600% and Young’s moduli down to ~10 2 Pa, 10 6 times softer than plastics and more than 102 times softer than all existing 3D printable elastomers. Moreover, the elastomers are thermostable and remain to be solid up to 180 °C, yet they are 100% solvent-reprocessable. Their extreme softness, stretchability, thermostability, and solvent-reprocessability bode well for future applications.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Biodegradation Studies of Polyhydroxybutyrate and Polyhydroxybutyrate- co -Polyhydroxyvalerate Films in Soil

Due to increased environmental pressures, significant research has focused on finding suitable biodegradable plastics to replace ubiquitous petrochemical-derived polymers. Polyhydroxyalkanoates (PHAs) are a class of polymers that can be synthesized by microorganisms and are biodegradable, making them suitable candidates. The present study looks at the degradation properties of two PHA polymers: polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-polyhydroxyvalerate (PHBV; 8 wt.% valerate), in two different soil conditions: soil fully saturated with water (100% relative humidity, RH) and soil with 40% RH. The degradation was evaluated by observing the changes in appearance, chemical signatures, mechanical properties, and molecular weight of samples. Both PHB and PHBV were degraded completely after two weeks in 100% RH soil conditions and showed significant reductions in mechanical properties after just three days. The samples in 40% RH soil, however, showed minimal changes in mechanical properties, melting temperatures/crystallinity, and molecular weight over six weeks. By observing the degradation behavior for different soil conditions, these results can pave the way for identifying situations where the current use of plastics can be replaced with biodegradable alternatives.

36 MATERIALS SCIENCE↗
NASA NTRS1991

New developments in thermally stable polymers

Advances in high-temperature polymers since 1985 are discussed with the emphasis on the chemistry. High-temperature polymers refer to materials that exhibit glass-transition temperatures greater than 200 C and have the chemical structure expected to provide high thermooxidative stability. Specific polymers or series of polymers were selected to show how the chemical structure influences certain properties. Poly(arylene ethers) and polyimides are the two principal families of polymers discussed. Recent work on poly(arylene ethers) has concentrated on incorporating heterocyclic units within the polymer backbone. Recent polyimide work has centered on the synthesis of new polymers from novel monomers, several containing the trifluoromethyl group strategically located on the molecule. Various members in each of these polymer families display a unique combination of properties, heretofore unattainable. Other families of polymers are also briefly discussed with a polymer from an AB maleimidobenzocyclobutene exhibiting an especially attractive combination of properties.

Hergenrother, Paul M.↗
NASA NTRS2009

Use of Atomic Oxygen for Increased Water Contact Angles of Various Polymers for Biomedical Applications

The purpose of this study was to determine the effect of atomic oxygen (AO) exposure on the hydrophilicity of nine different polymers for biomedical applications. Atomic oxygen treatment can alter the chemistry and morphology of polymer surfaces, which may increase the adhesion and spreading of cells on Petri dishes and enhance implant growth. Therefore, nine different polymers were exposed to atomic oxygen and water-contact angle, or hydrophilicity, was measured after exposure. To determine whether hydrophilicity remains static after initial atomic oxygen exposure, or changes with higher fluence exposures, the contact angles between the polymer and water droplet placed on the polymer s surface were measured versus AO fluence. The polymers were exposed to atomic oxygen in a 100-W, 13.56-MHz radio frequency (RF) plasma asher, and the treatment was found to significantly alter the hydrophilicity of non-fluorinated polymers. Pristine samples were compared with samples that had been exposed to AO at various fluence levels. Minimum and maximum fluences for the ashing trials were set based on the effective AO erosion of a Kapton witness coupon in the asher. The time intervals for ashing were determined by finding the logarithmic values of the minimum and maximum fluences. The difference of these two values was divided by the desired number of intervals (ideally 10). The initial desired fluence was then multiplied by this result (2.37), as was each subsequent desired fluence. The flux in the asher was determined to be approximately 3.0 x 10(exp 15) atoms/sq cm/sec, and each polymer was exposed to a maximum fluence of 5.16 x 10(exp 20) atoms/sq cm.

deGroh, Kim↗