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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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The synthesis of a chloro-functionalized six-membered cyclosilazane (Si5N) is reported on. Subsequent reductive polymerizations yielded low molecular weight polysilazanes. 1 H and 29 Si NMR characterization suggest the identity of the reducing metal influences the polysilazane structure.Furthermore, optical characterization is consistent with extended σ-conjugation upon polymerization.
The inherent crystallinity of metal–organic framework (MOF) catalysts offers the possibility to understand the structure of the active site at the molecular level. This property is often lacking in traditional amorphous supports. Cr-SIM-NU-1000, a MOF-supported Cr 3+ heterogeneous catalyst, is shown to be competent for ethylene polymerization after activation with AlEt 2 Cl (DEAC), producing crystalline linear polyethylene (PE). The polymer produced has a low polydispersity (D = 2.0), in marked contrast to the Phillips supported chromium catalyst, Cr@SiO 2 (D ~ 8–65). Cr-SIM-NU-1000 achieves a turnover frequency of 2.6 × 10 3 h –1 under 40 bar ethylene pressure at room temperature, with corresponding PE productivity of 1.3 × 10 5 g PE mol –1 Cr per h. Single crystal X-ray diffraction (SC-XRD) of the pre-catalyst was conducted by collecting a structure of alkyl aluminum (DEAC) co-catalyst treated Cr-SIM-NU-1000. This crystal structure provides insight into the interactions between DEAC co-catalyst and Cr active site, revealing a Cr–C bond after treatment with DEAC. Furthermore, DEAC is crystallographically resolved at the terminal oxy-ligands of the node and likely also exists within the window pores of the framework between nodes, based on electron density mapping. Cr-SIM-NU-1000 offers the opportunity to study a structurally well-defined olefin polymerization system, with atomically precise characterization of the pre-catalyst structure. Furthermore, this allows the proposal of a mechanism and feeds into future development of next-generation heterogeneous catalyst systems.
Polymeric graphitic carbon nitride (gCN) materials have received great attention in the fields of photo and electrocatalysis due to their distinct properties in metal-free systems with high physicochemical stability. Nevertheless, the activity of undoped gCN is limited due to its relatively low specific surface area, low conductivity, and poor dispersibility. Doping Gd atoms in a gCN matrix is an efficient strategy to fine-tune its catalytic activity and its electronic structure. Herein, the influence of various wt% of gadolinium (Gd) doped in melon-type carbon nitride was systematically investigated. Gadolinium-doped graphitic carbon nitride (GdgCN) was synthesized by adding gadolinium nitrate to dicyandiamide during polymerization. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results revealed that the crystallinity and the morphological properties are influenced by the % of Gd doping. Furthermore, X-ray photoelectron spectroscopy (XPS) studies revealed that the gadolinium ions bonded with nitrogen atoms. Complementary density functional theory (DFT) calculations illustrate possible bonding configurations of Gd ions both in bulk material and on ultrathin melon layers and provide evidence for the corresponding bandgap modifications induced by gadolinium doping.
Nylons, a major class of synthetic polyamides, are widely used due to their excellent mechanical strength, thermal stability, and chemical resistance. Conventional nylon production relies on the polymerization of lactams or stoichiometric nylon salts. However, applying these approaches to unconventional precursors such as bio-derived glutaric acid produces polymers with low molecular weight and limited applications. To address these challenges, we demonstrated that chemically-synthesized nylon diads enable the production of higher-molecular-weight polyamides compared with traditional salts. We then identified a biosynthetic approach using amide synthetases to convert unprotected bifunctional substrates into nylon-relevant diads. Using a cofactor regeneration system, enzymatic diad synthesis was scaled to produce sufficient material for laboratory-scale characterization and solid-state polymerization. Amide synthetases demonstrated broad substrate scope, catalyzing the regioselective assembly of diverse nylon-relevant diacids, diamines, and ω-amino acids. This strategy offers a novel route to synthesize challenging nylon monomers and advances production of bioderived nylons.
We have used coarse-grained molecular dynamics simulations to understand the effect of cation size on ion diffusion in polymerized ionic liquids at temperatures well above the glass transition temperature of the polymers. We investigated dependencies of the diffusion constant on the cation radius and static dielectric constant and interpreted these results in terms of underlying structural changes, and decoupling phenomenon. We have found non-monotonic effects of the cation radius on the diffusion constant, with a maximum at an intermediate radius resulting from two different size dependent effects. Changes in the radial distribution functions characterizing spatial distribution of cations with respect to anions result in a monotonic increase in the coordination number. This yields an increase in the effective interaction energy as a function of cation radius, which can explain the decrease in the diffusion constant. This increase is counteracted at small cation radii by a corresponding increase in decoupling of cation and anion dynamics. In addition, the diffusion constant is found to increase on increasing the static dielectric constant for all radii of the cations. These results highlight the significant role of decoupling in designing polymerized ionic liquids with an enhanced diffusion constant of cations.
Nucleate pool boiling heat transfer and its ebullient dynamics in polymeric solutions at atmospheric pressure saturated conditions are experimentally investigated. Three grades of hydroxyethyl cellulose (HEC) are used, which have intrinsic viscosity in the range 5.29 ≤ [ η ] ≤ 10.31 [dl/g]. Their aqueous solutions in different concentrations, with zero-shear viscosity in the range 0.0021 ≤ η 0 ≤ 0.0118 [N∙s/m 2 ], exhibit shear-thinning rheology in varying degrees, as well as gas–liquid interfacial tension relaxation and wetting. Boiling heat transfer in solutions with constant molar concentrations of each additive, which are greater than their respective critical polymer concentration C * , is seen to have anomalous characteristics. There is degradation in the heat transfer at low heat fluxes, relative to that in the solvent, where the postnucleation bubble dynamics in the partial boiling regime is dominated by viscous resistance of the polymeric solutions. At higher heat fluxes, however, there is enhancement of boiling heat transfer due to a complex interplay of pseudoplasticity and dynamic surface tension effects. The higher frequency vapor bubbling train with high interfacial shear rates in this fully developed boiling regime tends to be influenced by increasing shear-thinning and time-dependent differential interfacial tension relaxation at the dynamic gas–liquid interfaces.
A single layer polymeric backsheet material has been evaluated for use in silicon PV modules and as a luminescent solar collector. Physical and optical properties of the backsheet have been examined after damp heat, thermal cycling, and UV exposure for two different polymeric grades and three different pigment options including white, transparent, and photo-luminescent. As the importance of developing a white backsheet that is cost-effective, recyclable, and reliable is evident, the increased availability and use of bifacial cells is bound to increase the demand for transparent backsheets as well. In today's market, the cost of a clear backsheet is significantly higher than a white backsheet which is motivation for research and development of new material options in this field. Results from these extensive tests reveal the need for continued research in white pigments and positive results in transparent and luminescent backsheet options.
State-of-the-art polymeric membranes are unable to perform the high-precision ion separations needed for technologies essential to a circular economy and clean energy future. Coordinative interactions are a mechanism to increase sorption of a target species into a membrane, but the effects of these interactions on membrane permeability and selectivity are poorly understood. We use a multilayered polymer membrane to assess how ion-membrane binding energies affect membrane permeability of similarly sized cations: Cu 2+ , Ni 2+ , Zn 2+ , Co 2+ , and Mg 2+ . We report that metals with higher binding energy to iminodiacetate groups of the polymer more selectively permeate through the membrane in multisalt solutions than single-salt solutions. In contrast, weaker binding species are precluded from diffusing into the polymer membrane, which leads to passage proportional to binding energy and independent of membrane thickness. Our findings demonstrate that selectivity of polymeric membranes can markedly increase by tailoring ion-membrane binding energy and minimizing membrane thickness.
Identifying plastics capable of chemical recycling to monomer (CRM) is the foremost challenge in creating a sustainable circular plastic economy. Polyacetals are promising candidates for CRM but lack useful tensile strengths owing to the low molecular weights produced using current uncontrolled cationic ring-opening polymerization (CROP) methods. Here, we present reversible-deactivation CROP of cyclic acetals using a commercial halomethyl ether initiator and an indium(III) bromide catalyst. Using this method, we synthesize poly(1,3-dioxolane) (PDXL), which demonstrates tensile strength comparable to some commodity polyolefins. Depolymerization of PDXL using strong acid catalysts returns monomer in near-quantitative yield and even proceeds from a commodity plastic waste mixture. Our efficient polymerization method affords a tough thermoplastic that can undergo selective depolymerization to monomer.
Polymers that simultaneously transport electrons and ions are paramount to drive the technological advances necessary for next-generation electrochemical devices, including energy storage devices and bioelectronics. However, efforts to describe the motion of ions or electrons separately within polymeric systems become inaccurate when both species are present. In this paper, we highlight the basic transport equations necessary to rationalize mixed transport and the multiscale materials properties that influence their transport coefficients. Potential figures of merit that enable a suitable performance benchmark in mixed conducting systems independent of end application are discussed. Practical design and implementation of mixed conducting polymers require an understanding of the evolving nature of structure and transport with ionic and electronic carrier density to capture the dynamic disorder inherent in polymeric materials.
Flow chemistry offers high reaction yield, kinetic control, improved safety, reliability, scalability, and greater degree of process control. Herein, hyperbranched polymer-grafted silica microparticles (HP-SMPs) are synthesized in a commercially available flow reactor through atom transfer radical polymerization. Initiator-anchored silica microparticles are obtained by in situ silanization in the flow reactor. Hyperbranched poly[2-(dimethylamino)ethylmethacrylate] chains are grafted onto the initiator-anchored SMPs through inimer–monomer ratio control. To demonstrate the efficiency and universality of this approach in grafting polymers onto SMPs, multiple hyperbranched polymeric structures are obtained by varying the inimer concentration. Dye absorption test is conducted to demonstrate the potential applications of HP-SMPs.
Abstract A plug flow reactor was constructed to scale the synthesis of metastable, phthalaldehyde-based polymers to achieve production rates of 1–2 kg per day. The flow-induced mixing and in-line polymerization quench and precipitation sequences resulted in improved polymer purity and long-term stability compared to the same materials made from a conventional batch process. Cryogenic rheology was used to probe the complex fluid dynamics encountered during the polymerization of PPA homopolymers. It is envisioned that this continuous flow manufacturing approach could be extended to other low ceiling temperature or aldehyde monomer systems to help implement and support a plastic circular economy. Graphical abstract
We show that the mechanical stability of perovskite thin films can be increased by an order of magnitude by nanocompositing with polymeric nanofibers using a scalable method. We discuss the increase in fracture resistance energy, Gc, in the nanocomposite samples with respect to nanofiber orientation. We demonstrate this platform with commodity polymeric nanofibers including nylon-6,6 and polyvinyl alcohol. The fiber network reduces the mechanical fragility of the PSCs by increasing their fracture energy several-fold, while maintaining comparable morphology, chemical composition, and device efficiencies to pristine perovskite. Improved power conversion efficiency stability of the nanocomposites under accelerated aging conditions is demonstrated. This platform is a promising advance toward the commercial viability of PSCs.
Fillers and pore formers are used in many materials at Kansas City National Security Campus (KCNSC) to fine tune density and stiffness. Current off-the-shelf options such as urea and Expancel do not always provide the desired properties. This project investigated several methods for introducing porosity in rigid polymers such as epoxy and polyurethane. This work was done at partnering universities to identify a variety of methods to create porous polymeric materials. The University of Oklahoma (OU) investigated emulsion templating of epoxy, where the epoxy is mixed with a surfactant and water to form an emulsion. The emulsion is then molded and cured. During the cure process, water droplets evaporate to form porous structures. Total porosity can be tuned by changing the concentration of water added to the polymer. The University of Kansas (KU) investigated the synthesis of phenolic microballoons by spray drying, as well as methods of incorporating removable porogens into epoxy and polyurethane materials to create polymeric foams.
In the formulations of many composite materials, polymeric materials are often used as binder materials to enhance processability, functionality, and safety during manufacturing. For instance, poly(ester urethane), such as Estane® 5703, is used in the formulation of PBX 9501, and vinyl copolymer elastomer (VCE) is used in the formulation of VCE/filler compos ites. The stability of these binders directly impacts the overall stability and performance of their composites. Estane and VCE are prone to hydrolytic degradation, with water sorption behavior playing a significant role in their long-term stability and aging behavior. Hence, it is critical to study their water sorption behavior under various humidity and tempera ture conditions. To improve the accuracy and reduce labor-intensive work involved in water sorption experiments, an automated Dynamic Vapor Sorption (DVS) system was employed, which can generate large datasets. To efficiently process and analyze these datasets, Python scripts were developed. These scripts not only streamlined data processing, but also accu rately derived the Arrhenius parameters related to water diffusion and sorption properties for the tested materials. This approach offers a robust framework for evaluating water trans port and sorption processes in polymeric materials and adds valuable capabilities to future water sorption testing efforts.
Polymeric vesicles, characterized by enhanced colloidal stability, excellent mechanical properties, controllable surface functionality, and adjustable membrane thickness, are extremely useful in nano- and bio-technology for potential applications as nanosized carriers for drugs and enzymes. However, a few preparative steps are necessary to achieve a unilamellar vesicle with a narrow size distribution. Herein, we report the spontaneous formation of unilamellar polymeric vesicles with nanometer sizes (<50 nm), fabricated by simply mixing diblock copolymers (P(EO-AGE)(2K-2K) and P(EO-AGE)(0.75K-2K)) with differing hydrophilic mass fractions in aqueous solutions. Depending on the mixing ratio of block copolymers and the temperature, the block copolymer mixtures self-assemble into various nanostructures, such as spherical and cylindrical micelles, or vesicles. The self-assembled structures of the block copolymer mixtures were characterized by small-angle neutron scattering, resulting in a phase diagram drawn as a function of temperature and the mixing condition. Notably, the critical temperature for the micelle-to-vesicle phase transition can be easily controlled by altering the mixing conditions; it decreases with an increase in the concentration of one of the block copolymers.
Two-photon polymerization (2PP), which is a three-dimensional micro/nano-scale additive manufacturing process, is used to fabricate component for small custom experimental packages (“targets”) to support laser-driven, high-energy-density physics research. Of particular interest is the use of 2PP to deterministically print millimeter-scale, low-density, and low atomic number (CHO) polymer matrices (“foams”). Deformation during development and drying of the foam structures remains a challenge when using certain commercial acrylic photo-resins. Acrylic resins were chosen in order to meet the low atomic number requirement for the foam; that requirement precludes the use of low-shrinkage organic/inorganic hybrid resins. Here, we compare the use of acrylic resins IP-S and IP-Dip. Infrared and Raman spectroscopy are used to quantify the extent of the polymerization during 2PP vs. UV curing. The mechanical strength of beam and foam structures is examined, particularly the degree of deformation that occurs during the development and drying processes. The magnitude of the shrinkage is quantified, and finite element analysis is used in order to simulate the resulting deformation. Capillary drying forces during development are shown to be small and are likely below the elastic limit of the foam log-pile structures. In contrast, the substantial shrinkage in IP-Dip (~5–10%) causes large shear stresses and associated plastic deformation, particularly near constrained boundaries and locations with sharp density transitions. Use of IP-S with an improved writing procedure results in a marked reduction in deformation with a minor loss of resolution.
We develop topological methods for characterizing the relationship between polymer chain entanglement and bulk viscoelastic responses. We introduce generalized Linking Number and Writhe characteristics that are applicable to open linear chains. We investigate the rheology of polymeric chains entangled into weaves with varying topologies and levels of chain density. To investigate viscoelastic responses, we perform non-equilibrium molecular simulations over a range of frequencies using sheared Lees–Edwards boundary conditions. We show how our topological characteristics can be used to capture key features of the polymer entanglements related to the viscoelastic responses. We find there is a linear relation over a significant range of frequencies between the mean absolute Writhe W r and the Loss Tangent tan ( δ ) . We also find an approximate inverse linear relationship between the mean absolute Periodic Linking Number L K P and the Loss Tangent tan ( δ ) . Our results show some of the ways topological methods can be used to characterize chain entanglements to better understand the origins of mechanical responses in polymeric materials.