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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Crystallization of Bottlebrush Statistical Copolymers of Polystyrene and Poly(ethylene oxide)

Here, bottlebrush statistical copolymers (BSCPs) with poly(ethylene oxide) (PEO) and polystyrene (PS) side chains grafted to a polynorbornene (PNB) backbone were synthesized by ring-opening metathesis polymerization (ROMP). The impact of the glassy PS side chains on the crystallization of the PEO side chains as a function of the backbone length, grafting densities, and fraction of the PS and PEO side chains is described. The bottlebrush architecture, where the side chains are anchored to the backbone, inherently constrains the mobility of PEO. Compared with the bulk crystallization temperature of PEO, the higher glass transition temperature of PS places further constraints on PEO crystallization. The limited mobility of PEO leads to cold crystallization behavior during heating. Reduced grafting densities, in turn, reduce side-chain crowding, leading to less extended pendant structures. The degree of crystallinity of PEO was found to decrease at lower grafting densities to a point where crystallization was not observed. The average distance between bottlebrush backbones increased linearly with the backbone length, suggesting that the backbone forms a distinct mesodomain. For BSCPs with asymmetric volume fractions of PS and PEO side chains, the degree of crystallinity of PEO increases with a change from cold crystallization to normal nucleation and growth during cooling, as a result of reduced constraints on PEO mobility by the glassy PS side chains.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Toward Optimization of Polymer Electrolytes by Electrochemical Characterization: Poly(pentyl malonate) versus Poly(ethylene oxide)

Ion transport in two polymer electrolytes, poly­(ethylene oxide) (PEO) and poly­(pentyl malonate) (PPM), mixed with lithium bis­(trifluoromethanesulfonyl)­imide (LiTFSI) is studied in the vicinity of the limiting current. The experimental measurements are in quantitative agreement with theoretical predictions based on the concentrated solution theory. The properties of two electrolytes are compared using a new plot wherein the length-normalized limiting current, i lim L, is plotted as a function of the length-normalized potential drop, Φlim/L, in symmetric cells with electrolyte thickness, L. We propose that electrolyte design should aim to obtain the largest values of i lim L and the smallest values of Φlim/L. Using this criterion, PPM/LiTFSI is a better polymer electrolyte than PEO/LiTFSI. We hope that PPM/LiTFSI will serve as a benchmark for developing next-generation polymer electrolytes.

Lee, Jaeyong↗
DOE OSTI2025

Operando TEM study of a working copper catalyst during ethylene oxidation

Active catalysts are typically metastable, and their surface state depends on the gas-phase chemical potential and reaction kinetics. To gain relevant insights into structure-performance relationships, it is essential to investigate catalysts under their operational conditions. Here, we use operando TEM combining real-time observations with online mass spectrometry (MS) to study a Cu catalyst during ethylene oxidation. We identify three distinct regimes characterized by varying structures and states that show different selectivities with temperature, and elucidate the reaction pathways with the aid of theoretical calculations. Our findings reveal that quasi-static Cu 2 O at low temperatures is selective towards ethylene oxide (EO) and acetaldehyde (AcH) via an oxometallacycle (OMC) pathway. In the dynamic Cu 0 /Cu 2 O oscillation regime at medium temperatures, partially reduced and strained oxides decrease the activation energies associated with partial oxidation. At high temperatures, the catalyst is predominantly Cu 0 , partially covered by a monolayer Cu 2 O. While Cu 0 is extremely efficient in dehydrogenation and eventual combustion, the monolayer oxide favors direct EO formation. These results challenge conclusions drawn from ultra-high vacuum studies that suggested metallic copper would be a selective epoxidation catalyst and highlight the need for operando study under realistic conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Establishing the Stability of Cross-Linked Poly(ethylene oxide) Blended with Poly(pentyl malonate) against Lithium Metal Anodes

This work focuses on an electrolyte obtained by infusing linear poly(pentyl malonate) (PPM) chains into cross-linked poly(ethylene oxide) (PEO). A lithium salt is added to enable ion transport. Obtaining this electrolyte is only possible because PPM is miscible with PEO irrespective of salt concentration. The properties of this electrolyte are compared against two benchmarks: an electrolyte obtained by infusing linear PEO into cross-linked PEO and cross-linked PEO with no added linear polymer. Measurements of storage moduli and ion transport efficacies are found to be similar across the three electrolytes, suggesting similar stability behavior against lithium metal anodes, based on current theoretical models. Instead, the PPM infused electrolyte outperforms the other two electrolytes. In the cycling tests, the current supported by the PPM infused electrolyte was a factor of 20 higher than that of the PEO infused electrolyte and a factor of 4 higher than that of the cross-linked PEO electrolyte. In the unidirectional plating experiments, the other two electrolytes fail after about 4 h or less, while the PPM containing electrolyte did not fail during the 140 h testing period. Insight into the nature of failure modes was obtained using synchrotron hard X-ray microtomography.

Gido, Lily [University of California, Berkeley]↗
DOE OSTI2026

A structural and electrochemical study of perfluoropolyether-poly(ethylene oxide) solid polymer electrolytes

Solid polymer electrolytes offer attractive safety, processability, and interfacial adhesion for enabling high–energy solid-state lithium batteries, but they are often limited by narrow oxidative stability windows and low lithium-ion transference numbers. In an attempt to broaden the electrochemical stability window and increase lithium-ion transference number of poly(ethylene oxide) (PEO)-based solid polymer electrolytes, we produce an optically clear, crosslinked membrane of PEO and perfluoropolyether (PFPE) using a mixed solvent method and subsequently infuse the membrane with a lithium salt. Structural and thermal analyses reveal nanoscale phase separation between fluorocarbon and hydrocarbon domains with characteristic spacings of 7–8 nm and an elevated glass transition for the hydrocarbon phase. Consistent with this, PFPE-containing membranes exhibit substantially lower ionic conductivity than PEO analogs (dry and plasticized). The transference number and electrochemical stability are similar to pure PEO. These results demonstrate that fluorination implemented as segregated nanoscale domains does not deliver the anticipated transport or stability benefits; instead, phase separation increases tortuosity and suppresses hydrocarbon-phase dynamics. The work underscores the importance of fluorine placement and morphology control, guiding the design of partially fluorinated solid polymer electrolytes toward architectures that avoid detrimental nanoscale phase separation.

Carden, Peyton [ORNL] (ORCID:0000000162296538)↗
DOE OSTI2025

Confocal Raman Microscopy for Measuring In Situ Temperature-Dependent Structural Changes in Poly(Ethylene Oxide) Thin Films

Crystallization from the melt is a critical process governing the properties of semi-crystalline polymeric materials. While structural analyses of melting and crystallization transitions in bulk polymers have been widely reported, in contrast, those in thin polymer films on solid supports have been underexplored. Herein, in situ Raman microscopy and self-modeling curve resolution (SMCR) analysis are applied to investigate the temperature-dependent structural changes in poly(ethylene oxide) (PEO) films during melting and crystallization phase transitions. By resolving complex overlapping sets of spectra, SMCR analysis reveals that the thermal transitions of 50 µm thick PEO films comprise two structural phases: an ordered crystalline phase and a disordered amorphous phase. The ordered structure of the crystalline PEO film entirely disappears as the polymer is heated; conversely, the disordered structure of the amorphous PEO film reverts to the ordered structure as the polymer is cooled. Broadening of the Raman bands was observed in PEO films above the melting temperature (67 °C), while sharpening of bands was observed below the crystallization temperature (45 °C). The temperatures at which these spectral changes occurred were in good agreement with differential scanning calorimetry (DSC) measurements, especially during the melting transition. The results illustrate that in situ Raman microscopy coupled with SMCR analysis is a powerful approach for unraveling complex structural changes in thin polymer films during melting and crystallization processes. Furthermore, we show that confocal Raman microscopy opens opportunities to apply the methodology to interrogate the structural features of PEO or other surface-supported polymer films as thin as 2 µm, a thickness regime beyond the reach of conventional thermal analysis techniques.

Koh, Miharu [Department of Chemistry, University o↗
DOE OSTI2024

Designing a Dynamic Material via Interlocking Kraft Lignin with Ultrahigh Molecular Weight Poly(ethylene oxide)

The environmental issues stemming from plastic waste and the excessive use of petroleum-based chemicals are both concerning and urgent. To effectively address this problem, we need to adopt a comprehensive approach involving developing more sustainable and renewable materials. These materials should be capable of demonstrating similar or even better performance than functional polymers synthesized from petroleum-based chemicals. Our research aims to develop more sustainable materials by leveraging the intrinsic characteristics of a natural polymer, lignin, a byproduct of the biorefinery industries. We utilized the three-dimensional branching structure of lignin as a material framework. We employed an approach to co-reactive melt processing of kraft lignin with aliphatic flexible chains of soft cross-linkers through the reaction of the cross-linker epoxy chain ends with lignin functional groups. Our study demonstrates that the interlocked structure formed from the co-blending of kraft lignin with ultrahigh molecular weight poly(ethylene oxide) and the cross-linking of lignin chains through a solvent-free process can manipulate the macromolecular interactions and relaxation. This manipulation results in materials that exhibit a wide range of thermomechanical properties and self-healing and shape memory effects, with drastically improved stiffness in a single material. We have explored the fundamental understanding of the macromolecular chain relaxation dynamics originating from the interlocking structure formation. In conclusion, this investigation utilized various techniques, including thermal, mechanical, rheology, and quasi-elastic neutron scattering.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Surface Charge Predicts the Presence of Cation Effects in Electrocatalysis

The identity of electrolyte cations has an important influence on the rates of many electrocatalytic reactions, but these effects are not always observed. Recently, we found that the surface charge of the catalyst, quantified by the potential of zero total charge (PZTC), is a useful heuristic for predicting when cation effects will be observed for the oxygen reduction reaction (ORR). Here, we demonstrate that this descriptor allows us to rationalize the observation or absence of cation effects across a range of conditions, reactions (the hydrogen evolution reaction, the ORR, methanol oxidation, ethylene glycol oxidation, glycerol oxidation, and glucose reduction) and metal surfaces (Pt, Pd, Ag, and Au). These results suggest that when the reaction’s operating potential is negative of the metal’s PZTC, electrolyte cations accumulate at the catalyst surface and influence reaction rates. As a result, when reactions occur positive of the PZTC, cation effects are not observed.

Cations↗
DOE OSTI2025

Mechanistic Insights into Adsorptive and Catalytic Reactions from Controllable Distributions of Metal Cations (Pd, Pt, Ni, Cr, Cu) as [M‐OH] +1 /1Al or M +2 /2Al in Zeolites

Anchoring divalent metal ions in the same zeolite framework with similar Si/Al ratio selectively as zeolite-bound M +2 or [M +2 -OH] +1 cationic species enables critical comparison of the species’ intrinsic reactivity for industrially and fundamentally relevant reactions. H-BEA zeolites with similar Si/Al ratios but differing framework Al siting were used to anchored multiple divalent metal cations (Ni, Pd, Pt, Cr, Cu) in the zeolite micropores. State-of-the-art infrared (IR) spectroscopy, electron paramagnetic resonance (EPR) measurements, including two-dimensional pulsed HYSCORE EPR, extended X-ray absorption fine structure (EXAFS), and density functional theory (DFT) calculations together provide unambiguous evidence for the selective formation of divalent metal cations as M +2 /2Al species (for H-BEA prepared in the conventional hydroxide media), and [M +2 OH] +1 /1Al species for H-BEA prepared in HF. Solid-state proton-decoupled triple-quantum magic-angle spinning (3Q MAS) NMR measurements confirmed contrasting Al distributions in the two H-BEA zeolites, which led to a contrasting divalent cation speciation. The reactivities of the two cationic species were explored for catalytic and adsorptive applications in both organometallic homogeneous and heterogeneous catalysis. This work demonstrates their divergent reactivity in ethylene dimerization, ethylene oxidation (Wacker process), selective catalytic reduction (SCR) of NO, NO adsorption, and methane oxidation. Both M +2 /2Al and [M +2 OH] +1 /1Al cations are both active for ethylene dimerization, but [M +2 OH] +1 /1Al species show higher reaction rates for each Pd, Ni, Pt. [M +2 OH] +1 /1Al is active for acetaldehyde formation in Wacker ethylene oxidation. A new active site for ethylene oligomerization is proposed that possesses a terminal OH group (Cr-OH) in Phillips catalysts evident by a nearly inactive isolated Cr +2 /2Al species that contrast an active Cr─OH motif.

Divalent metal cations in a zeolite↗
DOE OSTI2025

Enhanced Ion Transport and Molecular Packing Stability in Asymmetric 2D Nanostructured π‐Conjugated Thieno[3,2‐b]Thiophene‐Based Liquid Crystal

Organic semiconductors based on liquid crystal (LC) molecules have attracted increasing interest. Here, in this work, two linear LCs based on 2,5‐bis(thien‐2‐yl)thieno[3,2‐b]thiophene (BTTT) mesogen are designed and synthesized, including BTTT/dEO3 with two symmetrically attached tri(ethylene oxide) groups and BTTT/mEO6 with one asymmetrically attached hexa(ethylene oxide) group. These two molecules have comparable functional‐group compositions but different molecular geometries, leading to their moderately different material performances. Both LCs show smectic mesophases with relatively low transition temperatures as confirmed by differential scanning calorimetry and polarized optical microscopy. A combination of experimental grazing incidence wide‐angle X‐ray scattering and molecular dynamics (MD) simulations reveals a herringbone packing motif of BTTT segments in both LCs while a smaller molecular tilt angle in BTTT/mEO6. Ionic conductivities are measured by doping LCs with different amounts of ionic dopants, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). BTTT/mEO6 shows better smectic phase stability to higher LiTFSI doping ratios. Both LCs exhibit similar ionic conductivities in the smectic phases, but BTTT/mEO6 outperforms BTTT/dEO3 by a factor of three in the amorphous phase at higher temperatures. MD simulations, performed to examine the ion solvation environment, reveal that BTTT/mEO6 is more efficient in coordinating Li‐ions and screening their interactions with TFSI‐ions which further promote ionic transport.

grazing incidence wide-angle X-ray scattering↗
DOE OSTI2026

Surface Reconstruction in Hydrated Amphiphilic Block Copolymer Thin Films Probed by Fluid Cell Atomic Force Microscopy

In many thin film materials, nuanced interplays of interfacial energies control the surface morphology and rearrangement. This work evaluates polymer−solvent interactions and solvent-driven surface reconstructions via ex situ and in situ fluid cell Atomic Force Microscopy (fc-AFM) analysis of amphiphilic block copolymer (BCP) thin films upon exposure to deionized (DI) water. We examine the differences in surface morphology, whole-film swelling, and force response in thin films of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) and polystyrene- block-poly[(allyl glycidyl ether)-co-(ethylene oxide)] (PS-b- P[AGE-co-EO]) processed into standing-up cylinder morphologies perpendicular to a silicon substrate (⊥C). Using Amplitude Modulation AFM (AM-AFM) and Amplitude-Phase Distance (APD) force spectroscopy, this work probes the mechanoresponsive nature of the dynamic surface layers of these films, unveiling surface layer stratification and surface chain rearrangement via minimal tip−sample stimulation. To help rationalize the observed reconfigurations, the energetic driving forces were estimated using the harmonic mean approximations of interfacial energies. Given the nonionizable nature of the minority P(AGE-co-EO) block and the energetic driving forces for chain mobility, this work shows how the elimination of unfavorable PS−water interfaces drives chain rearrangement and coverage of the PS surface by chains of the hydrophilic block. This work highlights considerations for increasing the heterogeneity and complexity of BCP thin films via random blocks and how those changes to local interfacial energies may drive larger scale film morphology reconstructions, with broader implications for tuning interface hydrophilicity.

Copolymers↗
DOE OSTI2024

Random Copolymerization of Substituted Dioxolanes: Rational Design of High-Performance Polymer Electrolytes

Polymer electrolytes enhance the safety of lithium-ion battery systems, but current state-of-the-art poly­(ethylene oxide)-based polymer electrolytes fail to achieve the electrochemical properties necessary for practical applications. We probed the impact of substituent density on the electrolyte performance by introducing methyl substituents into the backbone of a series of poly­(1,3-dioxolane) (PDXL)-based copolymers. The polymerization of 1,3-dioxolane (DXL) and 4-methyl-1,3-dioxolane (MeDXL) yielded a series of random copolymers that were amorphous above 10% MeDXL incorporation. The copolymers with 10 and 20% MeDXL incorporation exhibited higher efficacies than those of either PDXL or poly­(ethylene oxide) (PEO), highlighting the use of methyl substituents to control the electrochemical properties of polymer electrolytes.

Rugh, Haley J↗
DOE OSTI2024

Mechanically and Thermally Robust Gel Electrolytes Built from A Charged Double Helical Polymer

Polymer electrolytes have received tremendous interest in the development of solid-state batteries, but often fall short in one or more key properties required for practical applications. Herein, a rigid gel polymer electrolyte prepared by immobilizing a liquid mixture of a lithium salt and poly(ethylene glycol) dimethyl ether with only 8 wt% poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) (PBDT) is reported. The high charge density and rigid double helical structure of PBDT lead to formation of a nanofibrillar structure that endows this electrolyte with stronger mechanical properties, wider temperature window, and higher battery rate capability compared to all other poly(ethylene oxide) (PEO)-based electrolytes. The ion transport mechanism in this rigid polymer electrolyte is systematically studied using multiple complementary techniques. Li/LiFePO 4 cells show excellent capacity retention over long-term cycling, with thermal cycling reversibility between ambient temperature and elevated temperatures, demonstrating compelling potential for solid-state batteries targeting fast charging at high temperatures and slower discharging at ambient temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Polysilaketals: High‐Performance Polyether‐Based Electrolytes with Tunable Disubstituted Silane Linkers

Abstract Polymer electrolytes exhibit higher energy density and improved safety in lithium‐ion batteries relative to traditionally used liquid electrolytes but are currently limited by their lower electrochemical performance. Aiming to access polymer electrolytes with competitive electrochemical properties, we developed the anionic ring‐opening polymerization (AROP) of cyclic silaketals to synthesize amorphous silicon‐containing polyether‐based electrolytes with varying substituent bulk of the general formula [OSi(R) 2 (CH 2 CH 2 O) 2 ] n (R=alkyl, phenyl). As opposed to previously reported uncontrolled polycondensation routes toward low molecular weight polysilaketals, AROP allows access to targeted molecular weights above the entanglement threshold of the polymers. The polysilaketal with the lowest steric bulk (P(OSi Me,Me ‐2EO)) exceeds the conductivity of poly(ethylene oxide) (PEO), a leading polymer electrolyte. To the best of our knowledge, this is the first solid polymer electrolyte to achieve this benchmark. Steric bulk in polysilaketals was found to impart stability and two bulkier polysilaketals, P(OSi Et,Et ‐2EO) and P(OSi Me,Ph ‐2EO), exhibited higher current fractions than PEO over a wide range of salt loadings. Moreover, the efficacy of P(OSi Et,Et ‐2EO) was competitive with that of PEO. Taken together, the tunable and competitive electrochemical properties of polysilaketals validate the systematic incorporation of silyl groups as a strategy to access high performance polymer electrolytes.

Rugh, Haley J.↗
DOE OSTI2025

Polysilaketals: High‐Performance Polyether‐Based Electrolytes with Tunable Disubstituted Silane Linkers

Polymer electrolytes exhibit higher energy density and improved safety in lithium-ion batteries relative to traditionally used liquid electrolytes but are currently limited by their lower electrochemical performance. Aiming to access polymer electrolytes with competitive electrochemical properties, we developed the anionic ring-opening polymerization (AROP) of cyclic silaketals to synthesize amorphous silicon-containing polyether-based electrolytes with varying substituent bulk of the general formula [OSi(R)2(CH2CH2O)2]n (R=alkyl, phenyl). As opposed to previously reported uncontrolled polycondensation routes toward low molecular weight polysilaketals, AROP allows access to targeted molecular weights above the entanglement threshold of the polymers. The polysilaketal with the lowest steric bulk (P(OSiMe,Me-2EO)) exceeds the conductivity of poly(ethylene oxide) (PEO), a leading polymer electrolyte. To the best of our knowledge, this is the first solid polymer electrolyte to achieve this benchmark. Steric bulk in polysilaketals was found to impart stability and two bulkier polysilaketals, P(OSiEt,Et-2EO) and P(OSiMe,Ph-2EO), exhibited higher current fractions than PEO over a wide range of salt loadings. Moreover, the efficacy of P(OSiEt,Et-2EO) was competitive with that of PEO. Taken together, the tunable and competitive electrochemical properties of polysilaketals validate the systematic incorporation of silyl groups as a strategy to access high performance polymer electrolytes.

Rugh, Haley J↗