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DOE OSTI2015

SISGR - Hydrogen Caged in Carbon-Exploration of Novel Carbon-Hydrogen Interactions

Hydrogen trapped in a carbon cage, captured through repulsive interactions, is a novel concept in hydrogen storage. Trapping hydrogen via repulsive interactions borrows an idea from macroscale hydrogen storage (i.e. compressed gas storage tanks) and reapplies these concepts on the nanoscale in specially designed molecular containers. Under extreme conditions of pressure, hydrogen solubility in carbon materials is expected to increase and carbon is expected to restructure to minimize volume via a mixed sp2/sp3 hydrogenated state. Thermodynamics dictate that pre-formed C-H structures will rearrange with increased pressure, yet the final carbon-hydrogen interactions may be dependent upon the mechanism by which hydrogen is introduced. Gas “trapping” is meant to denote gas present in a solid in a high density, adsorbed-like state, when the external pressure is much less than that necessary to provide a comparable fluid density. Trapping thus denotes a kinetically metastable state rather than thermodynamic equilibrium. This project probed mechanochemical means to polymerize select hydrocarbons in the presence of gases, in an attempt to form localized carbon cages that trap gases via repulsive interactions. Aromatic, polyaromatic, and hydroaromatic molecules expected to undergo cyclo-addition reactions were polymerized at high (~GPa) pressures to form extended hydrogenated amorphous carbon networks. Notably, aromatics with a pre-existing internal free volume (such as Triptycene) appeared to retain an internal porosity upon application of pressure. However, a high photoluminescence background after polymerization precluded in situ identification of trapped gases. No spectroscopic evidence was found after depressurization that would be indicative of pockets of trapped gases in a localized high-pressure environment. Control studies suggested this measurement may be insensitive to gases at low pressure. Similarly, no spectral fingerprint was found for gas-imbued spherical carbon nanoshells, even after chemical “capping” of the gas-imbued nanoshells to limit gas diffusivity. Subsequently, spectral probes of gas vibrational modes adsorbed in various carbon nanostructures (including activated carbons, single-wall carbon nanotubes, polymers of intrinsic microporosity (PIMs), and UV-irradiated PIMs with decreased pore size) were found only at high pressure. The vibrational mode of the adsorbed film became perturbed in high density films, and the perturbation was sensitive to surface functional groups, pore size, and pore dimension. Experimental results were corroborated with first-principle modeling using density functional theory. Development of semi-empirical correlations that relate the spectral features to pore dimension, geometry, and chemical potential of the adsorbed film are on-going.

08 HYDROGEN↗

DOE OSTI2016

Exploratory Project: Rigid nanostructured organic polymer monolith for in situ collection and analysis of plant metabolites from soil matrices

Plant metabolites released from litter leachates and root exudates enable plants to adapt and survive in a wide range of habitats by facilitating resource foraging and plant-organismal interactions, and could influence soil carbon storage. The biological functions of these plant inputs and the organismal interactions they facilitate in soil are strictly governed by their composition and molecular identity. Our current understanding about the molecular identity of exudates is based on physiological studies that are done in soil-less axenic cultures. On the other hand, ecological studies that rely on isotope labeling to track the fluxes of carbon from plants to soil have found the complexities of soil-microbe matrices as an insurmountable barrier to undertake any meaningful molecular level characterization of plant inputs. Although it is constantly advocated to undertake a molecular level identification of the dynamicity of plant metabolites in soils, the complexity of soil system has thus far prevented any such endeavors. We developed polymeric probes through in-situ polymerization of poly(styrene-co-vinylbenzyl chloride-co-divinylbenzene) to elucidate the chemical environment of the soil to which the plant roots are exposed. Hypercrosslinking of the polymeric probes through an in-situ Friedel-Crafts alkylation significantly increased the surface area and the sorption capacity of the probes. Surface functionalization of the probes using a hybrid approach was also attempted. The efficacy of these probes was tested using batch equilibration. Scanning electron microscopy revealed extensive modification of the surface of the probes through hypercrosslinking. The probes exhibited a lower site specific sorption (slope of Freundlich adsorption isotherm close to unity) and percent recovery of the sorbed compounds from the probes were >70, indicating a predominance of reversible sorption. Further we imparted specificity to this copolymer matrix by using molecular-template imprinting approach for the selective capture of less abundant plant metabolites from a crowded soil/litter leachate. Our results suggests that i) the root exudate pattern of plants is highly dependent on the nutrient status of the plant, with greater specificity of root exudation occurring in growing medium with low available form of nutrients, ii) the chemical composition of root exudation is a function of the distance of sampling from the source-roots, with the composition of root exudation being more enriched in polar metabolites farther from the source-roots, iii) Further we demonstrated that the compounds present in real root exudates diffuse farther from the source roots than those in artificial root exudates that are traditionally used. Thus, our project highlights how the soil matrix is instrumental in modifying the chemical composition of root exudates, and highlights that, apart from the plant physiology, the specificity and function of root exudates is also modified by environmental factors.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2016

Final Report for Project titled High Thermal Conductivity Polymer Composites for Low-Cost Heat Exchangers

Heat exchangers (HXs) are critical components in a wide range of heat transfer applications, from HVAC (Heating Ventilation and Cooling) to automobiles to manufacturing plants. They require materials capable of transferring heat at high rates while also minimizing thermal expansion over the usage temperature range. Conventionally, metals are used for applications where effective and efficient heat exchange is required, since many metals exhibit thermal conductivity over 100 W/m K. While metal HXs are constantly being improved, they still have some inherent drawbacks due to their metal construction, in particular corrosion. Polymeric material can offer solution to such durability issues and allow designs that cannot be afforded by metal construction either due to complexity or cost. A major drawback of polymeric material is their low thermal conductivity (0.1-0.5? W/mK) that would lead to large system size. Recent improvements in the area of filled polymers have highlighted the possibility to greatly improve the thermal conductivity of polymeric materials while retaining their inherent manufacturing advantage, and have been applied to heat sink applications. Therefore, the objective of this project was to develop a robust review of materials for the manufacturing of industrial and commercial non-metallic heat exchangers. This review consisted of material identification, literature evaluation, as well as empirical and model characterization, resulting in a database of relevant material properties and characteristics to provide guidance for future heat exchanger development.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Final Research Performance Report - Small Molecular Associative Carbon Dioxide (CO 2 ) Thickeners for Improved Mobility Control

The initial objective of this project was to promote the application of a CO 2 thickener for improved mobility control during CO 2 EOR based on solubility tests, viscosity tests, and core floods. Ultimately, it was demonstrated that the CO 2 -soluble polymeric thickeners are much better suited for use a CO 2 -soluble conformance control agents for diverting the flow of CO 2 away from thief zones. Our team generated several effective small molecule CO 2 thickeners with ARPA-e funding. Unfortunately, none of these small molecule thickeners could dissolve in CO 2 without the addition of unacceptably large amounts of hexane or toluene as a co-solvent Therefore none were viable candidates for the core flooding studies associated with NETL award. Therefore during the entire core flood testing program associated with this NETL award, our team used only the most promising polymeric CO 2 thickener, a polyfluoroacrylate (PFA). In order to produce an environmentally benign polymer, the monomer used to make the new polymers used in this study was a fluoroacrylate that contains only six fluorinated carbons. We verified CO 2 solubility with a phase behavior cell. The thickening potential of all polymer samples was substantiated with a falling ball viscometer and a falling cylinder viscometer at Pitt. Two different viscometers were used to determine the increase in CO 2 viscosity that could be achieved via the dissolution of PFA. Praxair, which has an interest in thickening CO 2 for pilot EOR projects and for waterless hydraulic fracturing, agreed to measure the viscosity of CO 2 -PFA solutions at no cost to the project. Falling cylinder viscometery was conducted at Pitt in our windowed high pressure phase behavior cell. Both apparatuses indicated that at very low shear rates the CO 2 viscosity increased by a factor of roughly 3.5 when 1wt% PFA was dissolved in the CO 2 2. Our team also planned thickener concentrations and compositions at Pitt for the core tests that were conducted at Special Core Analysis Laboratories, Inc., (SCAL) in Midland, TX, where the ability for PFA to reduce CO 2 mobility in a core was then tested. During the beginning of these tests, the PFA polymer was then shown to impart reasonable improvements in mobility control during the SCAL core tests; as the CO 2 -PFA solution displaced CO 2 from the core at a constant volumetric flow rate, the pressure drop increased as expected. However, as the test progressed, there was clear and surprising evidence of dramatic reductions in core permeability due to PFA adsorption, especially for sandstones. For example, as the CO 2 -PFA solution displaced pure CO 2 from sandstone and limestone cores, the pressure drop increased by factors of multiple hundreds to over a thousand. It was subsequently demonstrated that the PFA injected into the core either (a) adsorbed strongly and irreversibly onto the rock surfaces, (b) deposited/precipitated within the rock, thereby blocking pores in a manner that could be dislodged by large changes in flow rate or flow direction, or (c) remained in solution and passed completely through the core. The loss of PFA to the porous media and the unacceptably large increases in pressure drop both indicated that PFA was inappropriate for CO 2 EOR mobility control, where thickener adsorption must be minimized and mobility reductions of only 10-100-fold are typically required. However, we realized that because the CO 2 -PFA solution could greatly reduce the permeability of porous media, it could serve as a near wellbore conformance control agent for blocking “thief zones”, where adsorption is acceptable and dramatic increases in pressure drop are desirable. These effects were more dramatic for sandstone than for limestone. Therefore, these PFA fluoroacrylate polymers can serve as a CO 2 -soluble conformance control agent for CO 2 -EOR, especially in sandstone formations. This injection of a single phase solution of CO 2 -PFA for permeability reduction is (to the best of our knowledge) the first report of a CO 2 -soluble conformance control additive. We also demonstrated that the optimal strategy for using CO 2 -PFA solutions for conformance control is analogous to the application of water-based polymeric gels; the CO 2 -PFA solution should first be injected only in an isolated thief zone to induce dramatic reductions in permeability only in that thief zone, and then CO 2 should be injected into all of the zones. Finally, it was noted that given the propensity of PFA to adsorb onto sandstone, the adsorption of PFA from CO 2 -PFA solutions onto cement surfaces promote the sealing of extremely fine cracks in casing cement.

02 PETROLEUM↗

DOE OSTI2017

Survey Study of Trunk Materials for Direct ATRP Grafting

In previous study, we demonstrated a new method to prepare polymeric fiber adsorbents via a chemical-grafting method, namely atom-transfer radical polymerization (ATRP), and identified parameters affecting their uranium adsorption capacity. However, ATRP chemical grafting in the previous study still utilized conventional radiation-induced graft polymerization (RIGP) to introduce initiation sites on fibers. Therefore, the objective of the present study is to perform survey study of trunk fiber materials for direct ATRP chemical grafting method without RIGP for the preparation of fiber adsorbents for uranium recovery from seawater.

36 MATERIALS SCIENCE↗

DOE OSTI2020

PDRD Project 19039 - All metal vacuum scroll pump development for tritium

Currently the United States relies on a single source, foreign company, Eumeca (formerly Normetex) for the supply of an all metal vacuum scroll pump to process tritium. This “one of a kind”, all metal, vacuum scroll pump utilizes no “wetted”, polymeric materials that degrade prematurely when exposed to tritium. U.S. based vacuum scroll pump suppliers typically utilize a polymer, Teflon®, as a tip seal material at the edge of the scroll impellers for proper pump function. Teflon® is known to degrade within a relatively short time frame (approximately 1 year) when continually exposed to tritium gas. This degradation results in “flaking” of the Teflon® material which results in particulate contamination of the process gas stream. While filtration of the particulate is possible, doing so requires additional maintenance which is costly in a glovebox environment. In addition, filtration can degrade pumping system performance as particulate collects in the filter media over time. To date, all of the well established U.S and European based vacuum scroll pump manufacturers have been uninterested in developing an all metal vacuum scroll pump that does not use a polymeric scroll tip seal. This position is taken as the vacuum scroll pump manufacturers do not see a large enough market to make it profitable for them to develop and market an all metal vacuum scroll pump. In the mid 2000s, one company, Air Squared, Inc., a small Original Equipment Manufacturer (OEM) specializing in design and fabrication of custom scroll vacuum pumps and compressors, was willing to pursue the effort. The first design effort incorporated Vespel® as a polymeric tip seal material. Results of this effort led to realizing the affect that the Met-Bel MB-601 metal bellows pump has on performance when used as a backing pump for an all metal vacuum scroll pump without a scroll tip seal. As a result, Air Squared subsequently designed an all metal vacuum scroll pump without a tip seal material for evaluation. Although the initial, all metal version of the Air Squared pump was found deficient in regard to scroll impeller stiffness, which resulted in scroll contact, general design and pump performance was verified to be adequate. SRS PDRD Project 19039 was launched in 2019 as a 3rd attempt with Air Squared, Inc. in regard to development of an all metal vacuum scroll pump for consideration as an equivalent to the Eumeca/ Normetex pump. The effort specified 300 series stainless steel for the scroll impellers, all metal sealing, and design to meet tritium throughput and ultimate vacuum requirements. In addition, a 60 psig design pressure rating requirement was specified for the pump containment boundary. The 3rd generation Air Squared pump has been designed, fabricated, and has received preliminary testing. Preliminary testing has indicated proper leak tightness and pump performance. However, work continues regarding development of a pumping chamber containment bellows that can be subjected to 66 psig without damage to the bellows. Work will continue in 2020 and 2021 to pursue a pumping chamber containment bellows that meets the pressure rating requirement.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2021

Nanoporous weakly coordinating anionic frameworks (Final Technical Report)

Under this award, we synthesized and characterized new weakly coordinating, anionic covalent organic frameworks. The motivation was to expand the class of covalent organic frameworks though the introduction of the first weakly coordinating anionic ones. The significance of the weakly coordinating anionic character of these frameworks is associated with the character of the counter (metal) cations in their pores. Those counter-cations, due to the inability to effectively coordinate to the pore walls, have a “naked”, and thus highly electrophilic, Lewis acidic character. Such properties are expected to translate to a number of interesting physical properties that can be potentially used for a range of energy-relevant applications. One of these applications is gas adsorption, separation, and storage. The electrophilic, Lewis acidic character of the counter-cations are expected to strongly bind to gas molecules entering the pores leading to higher gas sorption capacities. Other applications include heterogeneous catalysis, ion exchange, and solid state ion conduction. Within the project we explored a range of chemical blocks, and tested synthesis conditions to polymerize these building blocks to form the target materials. In particular, we focused on materials with group 15 elements like phosphorus in the oxidation state +5 and the coordination number 6, that have a formal -1 charge. The synthesis of such materials is challenging because its success depends on the absence of residual monomeric and oligomeric side-products in the pores, and the absence of significant framework interpenetration. Crystalline forms of these materials require sufficient reversibility of the polymerization reaction (which is difficult to achieve because group 15 elements like P tend to make strong covalent bonds with neighbored elements), as well as suitable polymerization rates that prevent the formation of kinetically controlled products. We had success with the preparation of anionic porous organic frameworks with anionic building blocks containing P(V)O6 octahedra synthesized through Yamamoto coupling reactions. These materials are non-crystalline because of the irreversible nature of the Yamamoto coupling reaction, but show porosity. The porosity and surface area can be significantly increased by co-reaction with electrostatically neutral co-reactants. Very high porosity and surface areas can be achieved when the materials are washed with hydrochloric acid. This method is commonly used to free products from Yamamoto coupling reactions from by-products. Indeed, this method removed by products from the pores of our materials, however it also led to the hydrolysis of the PO6 octahedra to form pending phosphonic acid groups (-PO3H)-groups in the frameworks (PA-POFs) which was actually not desired. Nonetheless, these materials showed high CO2 sorption capacities. In addition, they show extremely high (actually record) sorption capacities for the removal of a range of common micropollutants such as bisphenol A (BPA) and 4-nitrophenol in water. BPA is a wide-spread organic pollutant and a known endocrine disruptor. The maximum adsorption capacity of BPA at equilibrium is found to be as high as 3,366 mg g-1 by Langmuir adsorption model, which is more than 10 times greater than peer materials. The polymer also rapidly removes various other organic micropollutants with more than 90% removal efficiencies. In addition, the PA-POF material can be regenerated at least five times by mild washing using methanol without significant loss in removal efficiency. This is significant advantage over commonly used activated carbon materials (that are in Brita water faucet filters, for example). Comparison studies showed that only materials with the phosphonate groups show extreme sorption although the number of PA group is actually small according to solid state NMR and EDX data. More research would be needed to investigate why this is (a possibility is that the phosphonate groups have a multiplying effect in which a PA-induced initial adsorption leads to the adsorption of much more adsorbate). The extreme sorption capabilities can also be visually seen when colored adsorbates such as 4-nitrophenol are used, as the adsorption of the nitrobenzene leads to the decoloration of the solution. We have produced three short videos that illustrate the sorption capabilities compared to two peer materials (activated carbon from dismantled Brita water filters, and a electrostatically neutral, chemically related, porous organic polymer, respectively).

36 MATERIALS SCIENCE↗

DOE OSTI2024

Aryl ether-free polymer electrolytes for electrochemical and energy devices

Anion exchange polymers (AEPs) play a crucial role in green hydrogen production through anion exchange membrane water electrolysis. The chemical stability of AEPs is paramount for stable system operation in electrolysers and other electrochemical devices. Given the instability of aryl ethercontaining AEPs under high pH conditions, recent research has focused on quaternized aryl ether-free variants. The primary goal of this review is to provide a greater depth of knowledge on the synthesis of aryl ether-free AEPs targeted for electrochemical devices. Synthetic pathways that yield polyaromatic AEPs include acid-catalysed polyhydroxyalkylation, metal-promoted coupling reactions, ionene synthesis via nucleophilic substitution, alkylation of polybenzimidazole, and Diels–Alder polymerization. Polyolefinic AEPs are prepared through addition polymerization, ring-opening metathesis, radiation grafting reactions, and anionic polymerization. Discussions cover structure–property–performance relationships of AEPs in fuel cells, redox flow batteries, and water and CO 2 electrolysers, along with the current status of scale-up synthesis and commercialization.

25 ENERGY STORAGE↗

DOE OSTI2022

Tailoring Fibre Structure Enabled by X-ray Analytics for Targeted Biomedical Applications

The rising interest in designing fibres via spinning techniques combining the properties of various polymeric materials into advanced functionalised materials is directed towards targeted biomedical applications such as drug delivery, wearable sensors or tissue engineering. Understanding how these functional polymers exhibit multiscale structures ranging from the molecular level to nano-, micro-and millimetre scale is a key prerequisite for their challenging applications that can be addressed by a non-destructive X-ray based analytical approach. X-ray multimodalities combining X-ray imaging, scattering and diffraction allow the study of morphology, molecular structure, and the analysis of nano-domain size and shape, crystallinity and preferential orientation in 3D arrangements. The incorporation of X-ray analytics in the design process of polymeric fibers via their nanostructure under non-ambient conditions (i.e. temperature, mechanical load, humidity…) allows for efficient optimization of the fabrication process as well as quality control along the product lifetime under operating environmental conditions. Here, we demonstrate the successful collaboration between the laboratory of Biomimetic Textiles and Membranes and the Center of X-ray Analytics at Empa for the design, characterisation and optimisation of advanced functionalised polymeric fibrous material systems.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2016

Investigating Biochemical and Developmental Dependencies of Lignification with a Click-Compatible Monolignol Analog in Arabidopsis thaliana Stems

Lignin is a key structural component of plant cell walls that provides rigidity, strength, and resistance against microbial attacks. This hydrophobic polymer also serves a crucial role in water transport. Despite its abundance and essential functions, several aspects of lignin biosynthesis and deposition remain cryptic. Lignin precursors are known to be synthesized in the cytoplasm by complex biosynthetic pathways, after which they are transported to the apoplastic space, where they are polymerized via free radical coupling reactions into polymeric lignin. However, the lignin deposition process and the factors controlling it are unclear. In this study, the biochemical and developmental dependencies of lignification were investigated using a click-compatible monolignol analog, 3-O-propargylcaffeyl alcohol (3-OPC), which can incorporate into both in vitro polymerized lignin and Arabidopsis thaliana tissues. Fluorescence labeling of 3-OPC using click chemistry followed by confocal fluorescence microscopy enabled the detection and imaging of 3-OPC incorporation patterns. These patterns were consistent with endogenous lignification observed in different developmental stages of Arabidopsis stems. However, the concentration of supplied monolignols influenced where lignification occurred at the subcellular level, with low concentrations being deposited in cell corners and middle lamellae and high concentrations also being deposited in secondary walls. Experimental inhibition of multiple lignification factors confirmed that 3-OPC incorporation proceeds via a free radical coupling mechanism involving peroxidases/laccases and reactive oxygen species (ROS). Finally, the presence of peroxide-producing enzymes determined which cell walls lignified: adding exogenous peroxide and peroxidase caused cells that do not naturally lignify in Arabidopsis stems to lignify. In conclusion, 3-OPC accurately mimics natural lignification patterns in different developmental stages of Arabidopsis stems and allows for the dissection of key biochemical and enzymatic factors controlling lignification.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2023

Assessment and Non-Destructive Evaluation of the Influence of Residual Solvent on a Two-Part Epoxy-Based Adhesive Using Ultrasonics

Polymers are increasingly being used in higher demanding applications due to their ability to tailor the properties of structures while allowing for a weight and cost reduction. Solvents play an important role in the manufacture of polymeric structures since they allow for a reduction in the polymer’s viscosity or assist with the dispersion of fillers into the polymer matrix. However, the incorrect removal of the solvent affects both the physical and chemical properties of polymeric materials. The presence of residual solvent can also negatively affect the curing kinetics and the final quality of polymers. Destructive testing is mainly performed to characterize the properties of these materials. However, this type of testing involves using lab-type equipment that cannot be taken in-field to perform in situ testing and requires a specific sample preparation. Here, a method is presented to non-destructively evaluate the curing process and final viscoelastic properties of polymeric materials using ultrasonics. In this study, changes in longitudinal sound speed were detected during the curing of an aerospace epoxy adhesive as a result of variations in polymer chemistry. To simulate the presence of residual solvent, samples containing different weight percentages of isopropyl alcohol were manufactured and tested using ultrasonics. Thermogravimetric analysis was used to show changes in the decomposition of the adhesive due to the presence of IPA within the polymer structure. Adding 2, 4, and 6 wt.% of IPA decreased the adhesive’s lap shear strength by 40, 58, and 71%, respectively. Ultrasonics were used to show how the solvent influenced the curing process and the final sound speed of the adhesive. Young’s modulus and Poisson’s ratio were determined using both the longitudinal and shear sound speeds of the adhesive. Using ultrasonics has the potential to non-invasively characterize the quality of polymers in both an in-field and manufacturing settings, ensuring their reliability during use in demanding applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Poly(ionic liquid)s with Dicationic Pendants as Gas Separation Membranes

Poly(norbornene)s and poly(ionic liquid)s are two different classes of attractive materials, which are known for their structural tunability and thermal stabilities, and have been extensively studied as gas separation membranes. The incorporation of ionic liquids (ILs) into the poly(norbornene) through post-polymerization has resulted in unique materials with synergistic properties. However, direct polymerization of norbornene-containing IL monomers as gas separation membranes are limited. To this end, a series of norbornene-containing imidazolium-based mono- and di-cationic ILs (NBM-mIm and NBM-DILs) with different connectivity and spacer lengths were synthesized and characterized spectroscopically. Subsequently, the poly(NBM-mIm) with bistriflimide [Tf2N−] and poly([NBM-DILs][Tf2N]2) comprising homo-, random-, and block- (co)polymers were synthesized via ring-opening metathesis polymerization using the air-stable Grubbs second-generation catalyst. Block copolymers (BCPs), specifically, [NBM-mIM][Tf2N] and [NBM-ImCnmIm] [Tf2N]2 (n = 4 and 6) were synthesized at two different compositions, which generated high molecular weight polymers with decent solubility relative to homo- and random (co)polymers of [NBM-DILs] [Tf2N]2. The prepared BCPs were efficiently analyzed by a host of analytical tools, including 1H-NMR, GPC, and WAXD. The successfully BCPs were cast into thin membranes ranging from 47 to 125 μm and their gas (CO2, N2, CH4, and H2) permeations were measured at 20 °C using a time-lag apparatus. These membranes displayed modest CO2 permeability in a non-linear fashion with respect to composition and a reverse trend in CO2/N2 permselectivity was observed, as a usual trade-off behavior between permeability and permselectivity.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2021

Design and Gas Separation Performance of Imidazolium Poly(ILs) Containing Multivalent Imidazolium Fillers and Crosslinking Agents

This work introduces a series of vinyl-imidazolium-based polyelectrolyte composites, which were structurally modified via impregnation with multivalent imidazolium-benzene ionic liquids (ILs) or crosslinked with novel cationic crosslinkers which possess internal imidazolium cations and vinylimidazolium cations at the periphery. A set of eight [C4vim][Tf2N]-based membranes were prepared via UV-initiated free radical polymerization, including four composites containing di-, tri-, tetra-, and hexa-imidazolium benzene ILs and four crosslinked derivatives which utilized tri- and tetra- vinylimidazolium benzene crosslinking agents. Structural and functional characterizations were performed, and pure gas permeation data were collected to better understand the effects of “free” ILs dispersed in the polymeric matrix versus integrated ionic crosslinks on the transport behaviors of these thin films. These imidazolium PIL:IL composites exhibited moderately high CO2 permeabilities (~20–40 Barrer), a 4–7× increase relative to corresponding neat PIL, with excellent selectivities against N2 or CH4. The addition of imidazolium-benzene fillers with increased imidazolium content were shown to correspondingly enhance CO2 solubility (di- < tri- < tetra- < hexa-), with the [C4vim][Tf2N]: [Hexa(Im+)Benz ][Tf2N] composite showing the highest CO2 permeability (PCO2 = 38.4 Barrer), while maintaining modest selectivities (αCO2/CH4 = 20.2, αCO2/N2 = 23.6). Additionally, these metrics were similarly improved with the integration of more ionic content bonded to the polymeric matrix; increased PCO2 with increased wt% of the tri- and tetra-vinylimidazolium benzene crosslinking agent was observed. This study demonstrates the intriguing interactions and effects of ionic additives or crosslinkers within a PIL matrix, revealing the potential for the tuning of the properties and transport behaviors of ionic polymers using ionic liquid-inspired small molecules.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Monolithic Polyepoxide Membranes for Nanofiltration Applications and Sustainable Membrane Manufacture

The present work details the development of carbon fiber-reinforced epoxy membranes with excellent rejection of small-molecule dyes. It is a proof-of-concept for a more sustainable membrane design incorporating carbon fibers, and their recycling and reuse. 4,4′-methylenebis(cyclohexylamine) (MBCHA) polymerized with either bisphenol-A-diglycidyl ether (BADGE) or tetraphenolethane tetraglycidylether (EPON Resin 1031) in polyethylene glycol (PEG) were used to make monolithic membranes reinforced by nonwoven carbon fibers. Membrane pore sizes were tuned by adjusting the molecular weight of the PEG used in the initial polymerization. Membranes made of BADGE-MBCHA showed rejection of Rose Bengal approaching 100%, while tuning the pore sizes substantially increased the rejection of Methylene Blue from ~65% to nearly 100%. The membrane with the best permselectivity was made of EPON-MBCHA polymerized in PEG 300. It has an average DI flux of 4.48 LMH/bar and an average rejection of 99.6% and 99.8% for Rose Bengal and Methylene Blue dyes, respectively. Degradation in 1.1 M sodium hypochlorite enabled the retrieval of the carbon fiber from the epoxy matrix, suggesting that the monolithic membranes could be recycled to retrieve high-value products rather than downcycled for incineration or used as a lower selectivity membrane. The mechanism for epoxy degradation is hypothesized to be part chemical and part physical due to intense swelling stress leading to erosion that leaves behind undamaged carbon fibers. The retrieved fibers were successfully used to make another membrane exhibiting similar performance to those made with pristine fibers.

Polymer Science↗

DOE OSTI2026

Co-Design of Charge Transport Superhighways to Connect Catalytic Sites in Soft Photoelectrochemical Systems

Efficient photon-to-electron-to-molecule conversion requires multi-length scale control over charge transport pathways, where electronic charges are delivered to catalytic sites under high mass transport flux. A fundamental question is how can we co-design charge transport pathways to promote efficient charge transfer to/from catalytic sites in complex three-dimensional architectures? Soft conducting polymer systems offer exceptional promise to provide three-dimensional charge transport networks, where electrolyte (ion and solvent) can interdiffuse to promote long-lived charge carriers and the molecular nature allows for strategic synthetic design of catalytic sites. Herein we combine theoretical and experimental approaches to investigate the earliest stages of photoelectrochemical deposition of near-surface catalytic sites (Pt) on soft bulk heterojunction polymeric semiconductors composed of a prototype donor (PTB7-Th) and a prototype acceptor (N2200) as a model system towards better understanding molecular catalyst-polymer site interactions. We focus initially on photoelectrochemical deposition of low Pt loadings, nanoparticle sizes (formed by progressive nucleation) below 20 nm, for both density functional theory (DFT) modeling studies and for spectroscopic characterization using surface-sensitive X-ray and UV-photoemission (XPS/UPS). DFT modeling of “n-type” N2200 slabs reveal for the first time that sulfur atoms in the thiophene units serve as the lowest-energy adsorption sites for single Pt atoms, while larger Pt clusters engage more complexly with both thiophene and naphthalene diimide (NDI) core sites. Changes in chemical composition observed by X-ray photoelectron spectroscopy (XPS) support the DFT predictions, and the angle-resolved measurements reveal that Pt nucleation initiates at subsurface sites which appear to be localized active domains that promote charge transport/transfer and enable vertical growth toward the surface. These results suggest that light-activated Pt nanoparticle deposition decorates energetically distinct sites, where photoactivity is dictated by the local energetics of those sites, and the fact that they represent the termini of charge transport “super-highways” – a small percentage of the total volume of the donor/acceptor polymeric active layer which carries most of the photocurrent generated during both Pt deposition and photoelectrochemical HER. We posit that these initial studies provide a foundational strategy for design of catalytic sites in the near surface regions of complex polymeric materials and advancing soft semiconductor-based photoelectrochemical systems. Achieving a nanometer-scale understanding of catalyst deposition and the impact of local composition and energetics on that placement, should ultimately provide the design guidelines (co-design) for a broad array of catalysts at sites that optimize that efficiency and maximize platform durability.

14 SOLAR ENERGY↗

NASA NTRS1973

A review of processable high temperature resistant addition-type laminating resins

An important finding that resulted from research that was conducted to develop improved ablative resins was the discovery of a novel approach to synthesize processable high temperature resistant polymers. Low molecular weight polyimide prepolymers end-capped with norbornene groups were polymerized into thermo-oxidatively stable modified polyimides without the evolution of void producing volatile materials. This paper reviews basic studies that were performed using model compounds to elucidate the polymerization mechanism of the so-called addition-type polyimides. The fabrication and properties of polyimide/graphite fiber composites using A-type polyimide prepolymer as the matrix are described. An alternate method for preparing processable A-type polyimides by means of in situ polymerization of monomeric reactants on the fiber reinforcement is also described. Polyimide/graphite fiber composite performance at elevated temperatures is presented for A-type polyimides.

Serafini, T. T.↗

NASA NTRS1976

The polymer-like organic material in the Orgueil meteorite

Results are reported for analysis of polymeric organic material contained in powder from the Orgueil chondrite, using a stepwise high-vacuum pyrolysis-gas chromatography-mass spectrometry technique. Pyrolysis products obtained include a series of alkanes and alkenes to C8, an extensive series of alkylbenzene isomers, thiophene, alkylthiophenes, benzothiophene, acetonitrile, acrylonitrile, benzonitrile, acetone, and phenol. Most of these products are shown to be similar both qualitatively and quantitatively to those previously obtained from solvent-extracted Allende powder, indicating a basically aromatic and heteroaromatic polymer matrix with short aliphatic bridges or side chains. The production of acrylonitrile, acetonitrile, and benzonitrile (common breakdown products of amino acids) from the insoluble organic material is taken to suggest that amino acids exist in an insoluble form, perhaps as peptides, in the meteorite's polymeric component. Similarities between the structure of the Orgueil polymeric material and terrestrial kerogen are discussed which raise the possibility that both might have been produced in part by similar reactions.

Bandurski, E. L.↗

NASA NTRS1977

Consideration of encapsulants for photovoltaic arrays in terrestrial applications

Long-term survivability of photovoltaic arrays and components in terrestrial environments will require development of adequate protective systems. Highly considered are polymeric encapsulants, a method which was successfully employed in space and aerospace applications to protect critical electrical circuitry. To be employable, however, the polymer encapsulants must themselves be chemically and mechanically resistant to failure in terrestrial service. Chemical resistance includes stability to the degrading actions of ultraviolet light, oxygen, moisture and elevated temperatures in sun rich areas. Programs are underway to identify and develop chemically stable encapsulant candidates. Chemical considerations aside, mechanical failures of the encapsulants must also be avoided in array designs. This paper discusses design considerations for avoiding mechanical failures of polymeric encapsulants, with emphasis on biaxial properties, thermal fatigue, and anisotropy and nonhomogeneity of material properties. The general principles to be presented evolved from actual failures of polymeric materials in engineering applications. Also included are brief remarks on the permeability of polymer materials to atmospheric gases.

Cuddihy, E. F.↗