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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Synergistic Evolution of Segmental Motion and Cooperative Relaxation within the Amorphous Phase of Organic Mixed Ionic-Electronic Conductors

Organic mixed ionic-electronic conductors (OMIECs) facilitate a variety of electrochemical processes and feature a heterogeneous microstructure composed of both crystalline and amorphous phases. However, structural evolution in amorphous regions during electrochemical doping remains poorly understood, limiting our understanding of mixed conduction mechanisms. Here, in this work, we develop operando chip calorimetry to probe amorphous phase evolution in poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS) under swelling and electrochemical (de)­doping. Our results reveal that amorphous regions providing ionic transport pathways and those within electronic transport channels undergo heterogeneous, yet synergistic, evolution during electrochemical modulation. The cooperative interplay between segmental motion and relaxation maintains ionic conductivity and intergrain electronic transport upon electrowetting and doping, while facilitating efficient ion hopping and adaptable chain conformations during dedoping. Such synergies are more pronounced in loose structures featuring a fibrillar morphology, which exhibit lower glass transition temperatures (T g ) and higher fragility (m). High-throughput robotic screening further establishes a strong correlation between elevated m/T g ratios and enhanced mixed conduction. These findings elucidate the role of the amorphous phase in the synthesis of OMIECs and underscore the potential of operando chip calorimetry in uncovering structure–property relationships in electroactive polymers.

amorphous phase↗
DOE OSTI2024

Formation of Disordered Cocontinuous Phases by Randomly Linked Star Copolymers

Cocontinuous polymeric nanostructures have garnered significant interest due to their ability to combine different properties of two separate polymer domains. Randomly linked copolymer networks have proven to be especially robust for formation of disordered cocontinuous phases across wide composition ranges (≈30 wt % or more). While theoretical treatments of microphase-separated networks have focused primarily on the role of random elastic forces imposed on the self-assembled nanostructures by virtue of the network architecture, experimental studies seeking to disentangle these contributions from other potential effects, such as dispersity in preferred interfacial curvatures, have been scarce. To provide insight into this matter, we here study the self-assembly of randomly linked star copolymers (RSCs), constructed by linking premade polymer arms of polystyrene (PS) and poly(d,l-lactide) (PLA) using 3, 4, and 6-functional connectors. This architecture yields similar distributions of preferred curvature as networks made using corresponding difunctional strands, but lacks the elastic forces imposed by a network architecture. Gravimetry and small-angle X-ray scattering, coupled with scanning electron microscopy, were performed to identify the percolation of PS/PLA RSCs. Remarkably, the 4-arm RSC system exhibited a disordered cocontinuous window of ≈25 wt %, indicating that dispersity in preferred curvature can in some cases be sufficient to robustly drive formation of this morphology. However, the other RSC architectures showed smaller cocontinuous ranges, which we interpret in terms of the influence of homopolymer stars in the 3-arm case and the narrower distribution of preferred interfacial curvatures in the 6-arm case. Finally, thin layers of interconnected porous PS were achieved by solution-processing, suggesting that RSCs have the potential to serve as a robust and easily processable cocontinuous polymeric nanomaterials in both bulk and membrane geometries.

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

Standalone Block Copolymer Nanoballoons: Decoupling Self-Assembly from Implementation in Nanomanufacturing

Here we report a facile method to produce isolatable hollow-core elastomeric vesicles, “nanoballoons”, prepared via block copolymer self-assembly in a polymer blend. Poly(isoprene-block-dimethylsiloxane) (PI-PDMS) diblock copolymers are blended with PDMS homopolymers (h-PDMS) as a “solvent” phase to template the self-assembly of PDMS-tethered vesicles with PI walls. The walls are subsequently crosslinked to yield mechanically stabilized elastomeric vesicles. The h-PDMS inner-core and matrix are separated from the vesicles by dialysis to yield the matrix-free nanoballoons. These objects, 0.3 – 1 μm in diameter, can be further reincorporated into a crosslinkable PDMS. Throughout the self-assembly, recovery, and reincorporation processes we apply several techniques including solvent dispersion/dynamic light scattering (DLS) measurements, transmission electron microscopy (TEM)/energy-dispersive X-ray spectroscopy (EDS), and small-angle X-ray scattering (SAXS) to provide a consilient body of evidence that the nanoballoon morphology is retained. Furthermore, this work presents advanced nanomanufacturing schema that illustrate the decoupling of the thermodynamic and dynamic factors that govern macromolecular self-assembly from the environment in which the self-assembled objects are deployed.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Rapid Access to Diverse Multicomponent Hierarchical Nanostructures from Mixed–Graft Block Copolymers

Multicomponent nanostructured materials assembled from molecular building blocks received wide attention due to their precisely integrated multifunctionalities. However, discovery of these materials with desirable composition and morphology was limited by their low synthetic scalability and narrow structural tuning window with given building blocks. Here, we report a scalable and diversity-oriented synthetic approach to hierarchically structured nanomaterials based on a few readily accessible building blocks. Mixed-graft block copolymers containing sequence-defined side chains were prepared through ring-opening metathesis copolymerization of three or four types of macromonomers. Intramolecularly defined interfaces promoted the formation of ordered hierarchical structures with lattice sizes tunable across multiple length scales. Finally, the same set of macromonomers were arranged and combined in different ways, providing access to diverse morphologies in the resultant structures.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Changes to the morphology and coefficient of thermal expansion in HDPE and UHMWPE following irradiation-based crosslinking

This work describes recent findings of the Los Alamos National Laboratory concerning the alterations to polyethylene’s (PE’s) mechanical and chemical properties after crosslinking via gamma irradiation. Three materials were examined as part of this study, including one HDPE and two UHMWPE specimens. Changes to degree of crystallinity (X C ) were qualitatively determined via measurements of density, and results suggest that X C is not necessarily correlated to crosslink density, depending on polymer manufacturing process and treatment following irradiation. TMA data suggests an anisotropic response in linear thermal expansion, and that the response may be more correlated to X C than crosslink density. Finally, FTIR analysis has led to the conclusion that oxidation occurs as a result of irradiation in open air, the degree of oxidation is proportional to the maximum radiation dose received, and that oxidation is largely a surface effect, penetrating no deeper than 1.5 mm. Due to time constraints, a full dataset could not be generated for changes in creep and thermal properties as a result of irradiation, and TMA analysis is only complete for one material tested in this study. These measurements are ongoing and will provide more context to the hypotheses drawn in this work.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Self-Assembly of Flexible Linear–Semiflexible Bottlebrush–Flexible Linear Triblock Copolymers

Block copolymer (BCP) self-assembly is a fundamental process in which incompatible blocks spontaneously form organized microstructures with broad practical applications. Classical understanding is that the domain spacing is limited by the contour length of the polymer backbone. Here, using a combination of molecular design, chemical synthesis, small-/wide-angle X-ray scattering, transmission electron microscopy, and electron tomography, we discover that this molecular picture does not hold for architecturally semiflexible BCPs. For strongly segregated linear–semiflexible bottlebrush–linear triblock copolymers, the size of the bottlebrush domain can be twice the bottlebrush backbone contour length. The mechanism of such anomalous self-assembly is likely that the interfacial repulsion between the incompatible blocks is large enough to pull a part of the linear end blocks into the bottlebrush domain. This effectively increases the bottlebrush domain size. Moreover, the semiflexible bottlebrush widens the regime for the cylinder morphology that is associated with the volume fraction of the end blocks fC SFB ∈ (0.10, >0.41). This window is much wider than that for flexible linear BCPs, fC F ∈ (0.14, 0.35), and that predicted by the recent self-consistent field theory for linear-bottlebrush BCPs of the same chemistry and molecular architecture. Finally, our experimental findings reveal previously unrecognized mechanisms for the self-assembly of architecturally complex BCPs.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Janus bottlebrush compatibilizers

Bottlebrush random copolymers (BRCPs), consisting of a random distribution of two homopolymer chains along a backbone, can segregate to the interface between two immiscible homopolymers. BRCPs undergo a reconfiguration, where each block segregates to one of the homopolymer phases, adopting a Janus-type structure, reducing the interfacial tension and promoting adhesion between the two homopolymers, thereby serving as a Janus bottlebrush copolymer (JBCP) compatibilizer. Here, we synthesized a series of JBCPs by copolymerizing deuterated or hydrogenated polystyrene (DPS/PS) and poly(tert-butyl acrylate) (PtBA) macromonomers using ruthenium benzylidene-initiated ring-opening metathesis polymerization (ROMP). Subsequent acid-catalyzed hydrolysis converted the PtBA brushes to poly(acrylic acid) (PAA). The JBCPs were then placed at the interface between DPS/PS homopolymers and poly(2-vinyl pyridine) (P2VP) homopolymers, where the degree of polymerization of the backbone (N BB ) and the grafting density (GD) of the JBCPs were varied. Neutron reflectivity (NR) was used to determine the interfacial width and segmental density distributions (including PS homopolymer, PS block, PAA block and P2VP homopolymer) across the polymer-polymer interface. Our findings indicate that the star-like JBCP with N BB = 6 produces the largest interfacial broadening. Increasing N BB to 100 (rod-like shape) and 250 (worm-like shape) reduced the interfacial broadening due to a decrease in the interactions between blocks and homopolymers by stretching of blocks. Decreasing the GD from 100% to 80% at N BB = 100 caused an increase the interfacial width, yet further decreasing the GD to 50% and 20% reduced the interfacial width, as 80% of GD may efficiently increase the flexibility of blocks and promote interactions between homopolymers, while maintaining relatively high number of blocks attached to one molecule. The interfacial conformation of JBCPs was further translated into compatibilization efficiency. Thin film morphology studies showed that only the lower N BB values (N BB = 6 and N BB = 24) and the 80% GD of N BB = 100 had bicontinuous morphologies, due to a sufficient binding energy that arrested phase separation, supported by mechanical testing using asymmetric double cantilever beam (ADCB) tests. These provide fundamental insights into the assembly behavior of JBCPs compatibilizers at homopolymer interfaces, opening strategies for the design of new BCP compatibilizers.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Degradation Effects at the Porous Transport Layer/Catalyst Layer Interface in Polymer Electrolyte Membrane Water Electrolyzer

The porous transport layer (PTL)/catalyst layer (CL) interface plays a crucial role in the achievement of high performance and efficiency in polymer electrolyte membrane water electrolyzers (PEMWEs). This study investigated the effects of the PTL/CL interface on the degradation of membrane electrode assemblies (MEAs) during a 4000 h test, comparing the MEAs assembled with uncoated and Ir-coated Ti PTLs. Our results show that compared to an uncoated PTL/CL interface, an optimized interface formed when using a platinum group metal (PGM) coating, i.e., an iridium layer at the PTL/CL interface, and reduced the degradation of the MEA. The agglomeration and formation of voids and cracks could be found for both MEAs after the long-term test, but the incorporation of an Ir coating on the PTL did not affect the morphology change or oxidation of IrO x in the catalyst layer. In addition, our studies suggest that the ionomer loss and restructuring of the anodic MEA can also be reduced by Ir coating of the PTL/CL interface. Optimization of the PTL/CL interface improves the performance and durability of a PEMWE.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2022

Unravelling the Role of Electron Acceptors for the Universal Enhancement of Charge Transport in Quinoid-Donor-Acceptor Polymers for High-Performance Transistors

The quinoid-donor-acceptor (Q-D-A) strategy has recently emerged as a promising approach for constructing high mobility semiconducting polymers. In order to fully explore the potential of this strategy in improving the charge transport and elucidating the structure-property-performance relationships in Q-D-A polymers, a series of new polymers with different electron acceptor units and backbone coplanarity have been synthesized and characterized. In this work, all of the resulting Q-D-A polymers exhibit much more planar backbone conformations in comparison to their donor-acceptor (D-A) counterparts. Moreover, organic field-effect transistors based on Q-D-A polymers exhibit excellent effective hole mobilities in a range of 0.44 to 3.35 cm 2 V –1 s –1 , most of which are orders of magnitude higher than those of their corresponding D-A polymers. Notably, the hole mobility of 3.35 cm 2 V –1 s –1 is among the highest for the quinoidal-aromatic polymers characterized by conventional spin-coating methods. Furthermore, the role of electron acceptors in Q-D-A polymers has been comprehensively investigated. Polymers with stronger acceptor units are more inclined to deliver edge-on lamellas, high film crystallinity, small effective hole masses, and decent operational stability. The detailed structure-property-device performance relationship will pave the way toward high performance semiconducting polymers using the potent Q-D-A strategy.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Wood-reinforced composites by stereolithography with the stress whitening behavior

In this study, poplar wood flour at various concentrations (1–10 wt%) is incorporated into a methacrylate-based resin via solution blending to fabricate wood-reinforced composites using stereolithography apparatus (SLA) 3D printing. Differential scanning calorimetry (DSC) along with Fourier transform infrared spectroscopy (FTIR) analysis shows the presence of a small amount of residual monomer in the printed samples. For the printed composites, the glass transition temperature (T g ) from dynamic mechanical analysis (DMA) decreases as more wood flour is incorporated, which indicates an increase in free volume occupied by polymer chains. The tensile strength is improved up to 17.3% from 21.1 MPa (no wood flour) to 24.7 MPa (1.0 wt% wood flour). The highest Young’s modulus reaches 323.8 MPa (2.0 wt% wood flour), which is 1.9-fold of that of the sample without wood flour. Moreover, the composites show “stress whitening” with the addition of wood flour during the uniaxial drawing. Morphology analysis of the tested samples show that the formation of microcraze and microvoids likely causing the stress whitening. This is the first study that demonstrates wood flour can be utilized in SLA 3D printed wood plastic composites (WPC) which can reinforce the printed products with a modest loading amount.

36 MATERIALS SCIENCE↗
DOE OSTI2023

2-Aminoanthracene Crystallization in Its Compatible Polystyrene Block: RAFT Synthesis and Enhanced Charge Retention in Pentacene Transistor Gate Dielectrics

We synthesized polystyrene-block-polyanthrylaminomethylstyrene (PS-b-PAAS) via RAFT reaction and side chain modification where the PAAS block is 50%. By blending 2-aminoanthracene (2AA) with PS-b-PAAS, the co-aggregation behavior of the PAAS block and 2AA within the thin film was observed by optical microscopy (OM) and x-ray diffraction. At 5 and 10 wt% of 2AA within the thin film, OM results showed a clear morphological difference between PS matrix and PS-b-PAAS matrix. Differences in the 2AA excited state lifetime in these matrices were also established using transient absorption spectroscopy (TAS). Blends were used as gate dielectrics in pentacene transistors. We compared characteristic voltage (Vc, an indicator of threshold voltage) before and after charging of PS-b-PAAS blended with unsubstituted PS and both polymers individually blended with 2AA. For blended PS-b-PAAS and PS, as the concentration of PS-b-PAAS increases, the decreased Vc especially with negative charging of the pentacene indicated a larger concentration of charge carriers induced by the dielectric film. The charging experiments also revealed that the unique structure formed by the 2AA/PS-b-PAAS blend significantly affected the charge storage capability of the organic field-effect transistors (OFET). Furthermore, this work demonstrates the novel co-aggregation structure in the dielectrics, and furthermore its impact on charge storage capability in pentacene OFETs.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Selective sequential infiltration synthesis of ZnO in the liquid crystalline phase of silicon-containing rod-coil block copolymers

The combination of block copolymer (BCP) thin film self-assembly and selective infiltration synthesis of inorganic materials into one BCP block provides access to various organic–inorganic hybrids. Here, we apply sequential infiltration synthesis, a vapor-phase hybridization technique, to selectively introduce ZnO into the organic microdomains of silicon-containing rod-coil diblock copolymers and a triblock terpolymer, polydimethylsiloxane (PDMS)-b-poly{2,5-bis[(4-methoxyphenyl)-oxycarbonyl]styrene} (PDMS-b-PMPCS) and PDMS-b-polystyrene-b-PMPCS (PDMS-b-PS-b-PMPCS), in which the PMPCS rod block is a liquid crystalline polymer. The in-plane cylindrical PDMS-b-PMPCS and core–shell cylindrical and hexagonally perforated lamellar PDMS-b-PS-b-PMPCS films were infiltrated with ZnO with high selectivity to the PMPCS. The etching contrast between PDMS, PS and the ZnO-infused PMPCS enables the fabrication of ZnO/SiO x binary composites by plasma etching and reveals the core–shell morphology of the triblock terpolymer.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Analytical Tools to Assess Polymer Biodegradation: A Critical Review and Recommendations

Many petroleum-derived plastic materials are highly recalcitrant and persistent in the environment, posing significant threats to human and ecological receptors due to their accumulation in ecosystems. In recent years, research efforts have focused on advancing biological methods for polymer degradation. Enzymatic depolymerization has emerged as particularly relevant for biobased plastic recycling, potentially scalable for industrial use. Biodegradation involves adsorption to the plastic solid surface, followed by an interfacial reaction, resulting in cleavage of bonds of polymer chains exposed on the surface. Here, widely varying substrate-specific kinetics are observed, with the polymer’s properties possessing a significant impact on the rate of this interfacial catalysis. Thus, there is a critical need for sensitive and accurate characterization of the material surface during and after interfacial depolymerization to fully understand the reaction mechanisms. Here, we provide a critical review of a range of techniques used in the analysis of material surfaces to characterize the chemical, topological, and morphological features relevant to the study of enzymatic biocatalysis, including microscopy techniques, spectroscopic techniques (e.g., X-ray diffraction analysis, Fourier transform infrared attenuated total reflectance spectroscopy, and mass spectrometry detection of analytes associated with degradation). Techniques for evaluation of surface energy and topology in their relevancy for sensitive detection of biological surface modifications are also discussed. In addition, this paper provides an overview of the strengths of these techniques and compares their performance in both sensitivity and throughput, including emerging techniques, which can be useful, particularly for the rapid analysis of the surface properties of polymeric materials in high-throughput screening of candidate biocatalysts. This research serves as a starting point in selecting and applying appropriate methodologies that provide direct evidence to the ongoing biotic degradation of polymeric materials.

Colachis, Matthew↗
DOE OSTI2021

Toward Optimizing Electrospun Nanofiber Fuel Cell Catalyst Layers: Polymer–Particle Interactions and Spinnability

We investigate the effect of the poly(acrylic acid) (PAA) carrier polymer concentration on the microstructure and rheological properties of catalyst inks for electrospun polymer–electrolyte membrane fuel-cell catalyst layers. Characterization of an ink microstructure using oscillatory shear rheology showed that the catalyst particles (platinum on carbon) are significantly agglomerated in the absence of PAA or an ionomer. Both the ionomer and PAA promoted the stability of the particles against agglomeration via electrosteric stabilization by adsorbing onto the particle surface. Increasing the PAA concentration increased the stability of the particles (or reduced the agglomerated structure) due to increasing PAA coverage onto the free surface area of the particles. However, beyond a certain increase in concentration, PAA was found to predominantly remain as an excess free polymer in the ink due to an insufficient free/available surface area on the particles for further PAA coverage. Extensional rheology measurements demonstrated that PAA enhances the extensional viscosities of the inks. Consequently, increasing the PAA concentration in the ink promoted the evolution of uniform nanofibers. However, beyond a certain concentration, a significant increase in the shear viscosities of the inks led to defective fiber morphologies because of the onset of flow instabilities. Electrochemical performance comparisons between catalyst layers with different PAA concentrations showed maximum performance at the PAA concentration that led to the least agglomerated structure of the catalyst, most uniform fiber morphologies, and low concentrations of free (non-adsorbing) PAA in the electrode. These results provide a rationale for optimization of electrospun catalyst nanofibers for both spinnability and electrochemical performance.

25 ENERGY STORAGE↗
DOE OSTI2025

Confinement-Driven Segregation Enables Glassy Polymer Hybrid Materials Featuring Disordered Hyperuniformity and Integrated Self-Healing

The blending of glassy copolymer-brush modified colloids with a viscoelastic linear copolymer featuring intrinsic self-healing enabled disordered hyperuniform hybrid materials that combined mechanical robustness with structural color, processability, environmental stability, and the ability to recover structure and properties after incurring physical damage via ‘integrated self-healing’. Symmetric linear n-butyl acrylate/methyl methacrylate (BA/MMA) were co-assembled with asymmetric glassy BA/MMA statistical copolymer brush (silica) particles. ‘Confinement-driven segregation’ resulted in a microphase-separated morphology in which the linear copolymer resided within the interstitial regions of a rigid (∼1 GPa) copolymer brush particle template with disordered hyperuniform microstructure. Diffusion of the self-healing copolymer additive into damage regions drove the recovery after damage, along with the restoration of structural color due to the materials hyperuniform microstructure. The synergistic action of intrinsic and extrinsic healing mechanisms could provide a versatile platform for the bottom-up fabrication of multifunctional hybrid materials with increased damage resistance and functional longevity.

36 MATERIALS SCIENCE↗
DOE OSTI2023

High-temperature low-humidity proton exchange membrane with “stream-reservoir” ionic channels for high-power-density fuel cells

The perfluorosulfonic acid (PFSA) proton exchange membrane (PEM) is the key component for hydrogen fuel cells (FCs). We used in situ synchrotron scattering to investigate the PEM morphology evolution and found a “stream-reservoir” morphology, which enables efficient proton transport. The short-side-chain (SSC) PFSA PEM is fabricated under the guidance of morphology optimization, which delivered a proton conductivity of 193 milliSiemens per centimeter [95% relativity humidity (RH)] and 40 milliSiemens per centimeter (40% RH) at 80°C. The improved glass transition temperature, water permeability, and mechanical strength enable high-temperature low-humidity FC applications. Performance improvement by 82.3% at 110°C and 25% RH is obtained for SSC-PFSA PEM FCs compared to Nafion polymer PEM devices. The insights in chain conformation, packing mechanism, crystallization, and phase separation of PFSAs build up the structure-property relationship. In addition, SSC-PFSA PEM is ideal for high-temperature low-humidity FCs that are needed urgently for high-power-density and heavy-duty applications.

25 ENERGY STORAGE↗
DOE OSTI2024

Effects of mercerization and fiber sizing of coir fiber for utilization in polypropylene composites

The use of natural fibers as an alternative to synthetic fibers for reinforcing composites is increasing. However, the poor interfacial adhesion between natural fibers and polymer matrices limits their applications. Several approaches have been considered to improve fiber-matrix adhesion via chemical and/or physical treatment. However, the effectiveness of these treatments varies based on the type of fiber, its source, and its composition. Thus, it is imperative to understand the effectiveness of treatment conditions. In this study, we investigated the influence of alkali treatment and fiber sizing on the chemical, thermal, morphological, and mechanical properties of coir fibers and the interface between coir fiber and polypropylene matrix. Further, it was found that using a 5 wt% sodium hydroxide solution for 6 h at room temperature was the optimal treatment condition that led to an improvement in tensile strength by 58%, tensile modulus by 71%, and elongation at break by 37% compared to untreated fibers, and an increment in interfacial shear strength (IFSS) between coir fibers and polypropylene matrix by 32%. The alkali treatment removed the fiber surface impurities, made the fiber surface rough, and enhanced the fiber crystallinity. Sizing of the alkali-treated fiber led to an improvement in IFSS by 87% with no modification of the fiber’s mechanical properties.

36 MATERIALS SCIENCE↗