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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Reversible Changes in the Grain Structure and Conductivity in a Block Copolymer Electrolyte

Here, we study the phase behavior of a triblock organic–inorganic hybrid copolymer, poly(polyhedral oligomeric silsesquioxane)-b-poly(ethylene oxide)-b-poly(polyhedral oligomeric silsesquioxane) (POSS-PEO-POSS)/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt mixture, as a function of temperature. The polymer exhibits a lamellar morphology both in the neat state and in the presence of salt. However, the average grain size increases substantially when the electrolyte is heated above 113 °C. The grain structure of this sample changes reversibly with temperature, that is, smaller grains reappear when the electrolyte is cooled below 113 °C. While annealing block copolymers at high temperatures often leads to an increase in the grain size, this change is generally irreversible. The reason for the reversible change in the grain structure of the POSS-PEO-POSS/LiTFSI electrolyte is discussed. The ionic conductivity of the electrolyte also exhibits reversible changes in this temperature window. Knowledge of the grain structure is crucial for understanding ion transport in nanostructured electrolytes.

25 ENERGY STORAGE↗
DOE OSTI2020

Phase Behavior of Diblock Copolymer–Homopolymer Ternary Blends with a Compositionally Asymmetric Diblock Copolymer

The phase behavior of ternary polymer blends comprising poly(cyclohexylethylene) (C) and polyethylene (E) homopolymers and a compositionally asymmetric CE diblock copolymer with f C = 0.67 was investigated, where f C is the volume fraction of C. Morphology was established in the phase prism (volume fractions of C, E, and CE vs. temperature) by optical transmission, small-angle X-ray scattering (SAXS), and small-angle neutron scattering (SANS) measurements. The locations of lamellar (LAM), hexagonally packed cylinders (HEX), and gyroid (GYR) ordered phases are shifted significantly towards lower fractions of C homopolymer compared to previous results obtained from ternary polymer blends with a symmetric diblock copolymer (f C = 0.5). Conversely, the Scott line of critical points, which delineates the boundary between single-phase disorder and macroscopic phase separation, remains virtually unchanged, coincident with the fraction of C homopolymer associated with the binary homopolymer blend critical composition. A central finding of this study is that the line of nearly congruent order-disorder transitions, where the LAM phase melts virtually directly into the disordered state, is decoupled in composition from that of the Scott line of critical points. A wide range of phase space between the compositions associated with the congruent transition and Scott line was identified as containing a microemulsion morphology. This study demonstrates that diblock copolymer compositional asymmetry significantly impacts the ordered phase regime but has a marginal effect on the region displaying macroscopic phase separation. It also provides useful guidance for tuning interfacial curvature, a crucial factor in the formation of bicontinuous microemulsions (BµEs).

36 MATERIALS SCIENCE↗
DOE OSTI2021

Orientation-Dependent Distortion of Lamellae in a Block Copolymer Electrolyte under DC Polarization

Lithium-salt-doped block copolymers have the potential to serve as solid electrolytes in rechargeable batteries with lithium metal anodes. In this work, we use small-angle X-ray scattering (SAXS) to study the structure of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) doped with bis-(trifluoromethylsulfonyl)amine lithium salt (LiTFSI) during direct current (dc) polarization experiments in lithiu-lithium symmetric cells. The block copolymer studied is nearly symmetric in composition, has a total molecular weight of 39 kg mol -1 , and exhibits a lamellar morphology at all studied salt concentrations. When ionic current is passed through the electrolyte, a salt concentration gradient forms that induces a spatial gradient in the domain spacing, d. The dependence of d on distance from the positive electrode, x, was determined experimentally by scanning the incident X-ray beam from one lithium electrode to the other. By studying the two-dimensional (2D) SAXS patterns as a function of azimuthal scattering angle, we find that lamellae with PS/PEO interfaces oriented perpendicular to the flow of ionic current (LAM ⟂ ) swell and contract to a greater degree than those with interfaces oriented parallel to the current direction (LAM || ). While domains with the LAM ⟂ do not provide direct conducting pathways between the electrodes, our analysis suggests that they play an important role in establishing the salt concentration gradient necessary for sustaining a large ionic current through greater expansion and contraction.

25 ENERGY STORAGE↗
DOE OSTI2021

Solvent Processing and Ionic Liquid-Enabled Long-Range Vertical Ordering in Block Copolymer Films with Enhanced Film Stability

Rapid and reliable processing methods for forming ordered block copolymer (BCP) materials with low defect density in a thin film geometry are required for many nanotechnology applications. Vertically aligned BCP structures, in particular, have applications ranging from nanolithography for electronics and photonics to nanoporous membranes for water remediation and novel batteries for flexible electronics. However, the attainment of nearly complete vertical orientational order of the BCP ordered phase remains challenging. Solvent-based techniques, such as direct immersion annealing (DIA) and solvent vapor annealing (SVA), have immense potential for these applications of BCP films, as it allows for tuning of their thermodynamic, structural, and chain mobility driven kinetic properties. We first demonstrate that DIA, using a judicious choice of binary solvent mixtures along with a relatively hydrophobic ionic liquid (IL), induces the rapid vertical ordering in polystyrene-b-polymethylmethacrylate (PS-PMMA) block copolymer in lamellar films. The IL establishes synergy to the binary solvent mixture of toluene and heptane to 1 create a near-neutral solvent environment for attaining the vertical microstructure of the BCP. Next, we show that IL can suppress the de-wetting of the PS-PMMA films to achieve long-range order using SVA in cylindrical films for long annealing times. Both vertical and horizontal morphology is attained in these films by selecting different solvent environments. Furthermore, attaining enhanced vertical and horizontal BCP structure with long-range defect-free order by tuning solvent quality and using additives like IL can render them useful for many nanotech applications.

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

Understanding Solution State Conformation and Aggregate Structure of Conjugated Polymers via Small Angle X-ray Scattering

Donor-acceptor (D-A) conjugated polymers are high-performance organic electronic materials that exhibit complex aggregation behavior. Understanding the solution state conformation and aggregation of conjugated polymers is crucial for controlling morphology during thin-film deposition and the subsequent electronic performance. However, a precise multiscale structure of solution state aggregates is lacking. Here, we present an in-depth small-angle X-ray scattering (SAXS) analysis of the solution state structure of an isoindigo-bithiophene-based D-A polymer (PII-2T) in chlorobenzene and decane as our primary system. Modeling the system as a combination of hierarchical fibrillar aggregates mixed with dispersed polymers, we extract information about conformation and multiscale aggregation and also clarify the physical origin of features often observed but unaddressed or misinterpreted in small-angle scattering patterns of conjugated polymers. The persistence length of the D-A polymer extracted from SAXS agrees well with a theoretical model based on the dihedral potentials. Additionally, we show that the broad high q structure factor peak seen in scattering profiles can be attributed to lamellar stacking occurring within the fibril aggregates and that the low q aggregate scattering is strongly influenced by the polymer molecular weight. Overall, the SAXS profiles of D-A polymers in general exhibit a sensitive dependence on the co-existence of fibrillar aggregate and dispersed polymer chain populations. We corroborate our findings from SAXS with electron microscopy of freeze-dried samples for direct imaging of fibrillar aggregates. Finally, we demonstrate the generality of our approach by fitting the scattering profiles of a variety of D-A polymers based on thieno-isoindigo (PTII-2T), diketopyrrolopyrrole (DPP2T-TT, DPP-BTZ, PDPP2FT-C- 16 ), naphthalenediimide (P(NDI2OD-T2)), and a conjugated block copolymer P3HT-b-DPPT-T. The results presented here establish a picture of the D-A polymer solution state structure and provide a general method of interpreting and analyzing their scattering profiles.

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

Nondestructive Photo-Cross-Linking of Microphase-Separated Diblock Polymers through Coumarin Dimerization

The effect of long-wavelength ultraviolet photocrosslinking on microphase-separated coumarin-containing block polymers was studied by photo-rheometry and small-angle X-ray scattering. This model system consisted of three photocrosslinkable diblock polymers of poly(methoxyethyl acrylate)-b-poly(hexyl methacrylate-co-coumarin methacrylate) with different volume fractions of the crosslinkable coumarin-containing block, which microphase separated into lamellar and cylindrical morphologies. All polymers stiffened upon exposure to 365 nm light, with much greater relative increases in moduli recorded for lamellae-forming polymers (ca. 3200% increase) compared to the cylinder-forming polymer (ca. 550% increase). Disordering transitions that were evident in uncrosslinked samples were no longer observed after crosslinking in the ordered state, and domain sizes were found to remain stable to heating. The photocrosslinking reaction only proceeded under active irradiation, indicating a high degree of spatiotemporal control over curing in this system. Finally, at constant concentration of couamarin within the crosslinkable block, the cure rate was largely independent of polymer composition, suggesting a constant local concentration of coumarin moieties within the segregated crosslinkable domains. Lastly, these findings establish a set of specific structure-property relationships governing the phase-selective photocrosslinking of diblock polymers that can guide the design of robust nanostructured materials.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2022

Self-Assembly of Partially Charged Diblock Copolymer-Homopolymer Ternary Blends

Ternary blends comprising of a diblock copolymer and the corresponding homopolymers provide ready access to a variety of morphologies, but the impact of charge on their phase behavior has not been studied extensively. Here, three partially charged ternary blends consisting of symmetric poly[(oligo(ethylene glycol) methyl ether methacrylate-co-oligo(ethylene glycol) propyl sodium sulfonate methacrylate)] (POEGMA#), polystyrene (PS), and POEGMA#-PS with different charge fractions were prepared, where # denotes the mole fraction of charged monomers in the POEGMA chain. Here, the phase behavior was systematically studied using small-angle X-ray scattering (SAXS), and isothermal phase diagrams at 120 °C were constructed. The resulting isothermal planes contain a wide lamellar (LAM) phase window with a slight deviation from symmetry for ion-containing ternary blends, due to the homopolymer size difference. Given the absence of any significant change in the phase diagrams as the charge fraction increases, the role of charge is primarily to increase the segregation strength in the ternary system, as in the case of partially charged diblock polymers. In addition, examination of the increase in domain size along the volumetrically symmetric isopleth reveals a “dry-brush” like swelling behavior of homopolymers in all three blends, presumably due to the space-filling nature of the oligomeric ethylene glycol side chains on POEGMA.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2023

Engineering Self-Assembled Domain Asymmetry in Solvent Vapor Annealed Block Copolymer–Homopolymer Blend Films

Thin-film block copolymer (BCP) self-assembly is a powerful approach to generate highly uniform nanopatterns across large areas, yet the symmetries of these nanopatterns are constrained by the relative volume occupied by each polymer block. Here, we present a conceptually new approach to circumvent this limitation by combining homopolymer (HP) blending with solvent vapor annealing (SVA), demonstrated here for ternary blends of a near-symmetric BCP with athermal, low molar mass HPs. Screening of BCP–HP interactions by a weakly selective solvent promotes entropically driven delocalization of HP throughout both blocks and enables assembly of metastable lamellae for volume fractions as high as 0.78. Subsequent brief thermal annealing induces HPs to withdraw to their enthalpically favored domains, sharpening domain interfaces on a time scale much shorter than pattern coarsening. This renders lamellar nanopatterns with tunable widths that can be transferred to other materials with high fidelity. Furthermore, the persistence of the metastable asymmetric lamellae upon thermal annealing is sensitive to film confinement, as they are preserved in submonolayer films but transition to horizontal cylinders in films more than one monolayer thick. SVA using a strongly selective solvent results in assembled morphologies aligned closely with expectations based on the total polymer blend composition, underscoring the key role of BCP–HP interactions in dictating domain asymmetry. Overall, this work details important principles for using SVA to mediate BCP–HP interactions in thin films, thereby presenting opportunities to engineer pathways for the assembly of well-ordered nanopatterns with designer feature asymmetry for lithographic or nanotexturing applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

Hydrolysis-Induced Morphology Evolution of Linear and Bottlebrush Block Copolymers in Thin Films with Acid Vapor or Photoacid Generators

The self-assembly of high-χ low-N block copolymers (BCPs) can give patterns with sub-10 nm full pitch, serving as a promising alternative to photolithographic methods. Here, in this work, we synthesized poly(solketal methacrylate)-block-polystyrene copolymers, PSM-b-PS, with various volume ratios of the two blocks. After hydrolysis of the PSM block into poly(glycerol monomethacrylate), PGM, the BCPs had both lamellar and cylindrical microdomain morphologies in the bulk phase and in thin films. In addition to our previously developed solid-state hydrolysis strategy involving trifluoroacetic acid vapor, we developed a new photoinduced solid-state hydrolysis using photoacid generators, PAGs, embedded within the polymer films. After exposure to UV followed by a postexposure baking or solvent vapor annealing, the BCPs transitioned from the disordered, phase-mixed state into laterally ordered cylindrical patterns. In comparison to linear BCPs that rely on a random copolymer layer to modify interfacial interactions with the substrate to promote an orientation of the microdomains normal to the interface, we found that the microdomains in bottlebrush multiblock copolymers oriented normal to the interface absent substrate modification due to the chain architecture.

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

Role of Bottlebrush Additives on the Structure of Block Copolymers in the Bulk and Thin Films

Blending block copolymers (BCP) with additives is a useful approach for controlling BCP morphology and properties. In athermal systems, blends of BCPs with polymer additives having very high molecular (M n ) mass generally result in macrophase separation. Bottlebrush polymers, which consist of a linear backbone and grafted side chains, present an interesting alternative where the overall M n of the system can be very large but the low M n side chains may drive miscibility with the BCP. Here, in this study, a bottlebrush with a polynorbornene backbone and polystyrene (PS) side chains is blended with PS-b-poly(methyl methacrylate) (PS-b-PMMA) of varying M n , and the resulting morphologies are examined in both the bulk and thin films. Two different M n of PS-b-PMMA were used in the bulk study, and the analysis of small-angle X-ray scattering data shows that the blends were miscible and lamellar at all concentrations. This deviates from reference series of both low and high M n linear polymer additives, which either showed morphological transitions from lamellae to cylinders (low M n ) or were immiscible at all mass fractions studied (high M n ). The relative molecular mass of the side chain (N SC ) and the corresponding component in the BCP (N A ) dictate the distribution of the bottlebrush throughout the BCP, analogous to BCP/linear blends or grafted nanoparticles in a homopolymer matrix. The studies on thin films show a thickness dependence for bottlebrush mass fractions at or above 0.17, a behavior which may be driven by conformational changes of the bottlebrush upon confinement.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Backbone Stitching in Bottlebrush Copolymer Mesodomains and the Impact of Side Chain Crystallization

We synthesized bottlebrush statistical copolymers (BSCPs) having poly­(ethylene oxide) (PEO) and poly­(dimethylsiloxane) (PDMS) side chains attached to a polynorbornene backbone. Small-angle X-ray scattering analysis showed that for densely grafted BSCPs, the scattering length density gradually transitions between the PEO and PDMS domains. For loosely grafted BSCPs, the polymer backbone formed a distinct mesodomain, with a lower electron and mass density than both the PEO and PDMS domains. The bottlebrush backbone essentially “stitches” the PEO and PDMS side chains, looping back and forth from the PEO to PDMS domains with the backbone segments oriented normal to the domain interfaces. Self-consistent field theory (SCFT) calculations validated the stitching of the backbone driven by the microphase separation of PEO and PDMS, along with a strong segmental order of the side chains in the melt. The reduced birefringence upon PEO crystallization suggests the disruption of the strong segmental order by the crystallization. Both the static intrinsic and the form birefringences of the BSCPs decreased upon PEO crystallization. Solid-state NMR confirmed the rigidity of PEO crystallites and the bottlebrush backbone. Self-assembly of BSCPs containing polyhedral oligomeric silsesquioxane (POSS) pendent groups was also evaluated by X-ray scattering, showing the formation of lamellar microdomains that inhibited POSS crystallization.

Hu, Mingqiu↗
DOE OSTI2025

Architecture-Dependent Thin Film Self-Assembly of Star Polystyrene-poly(2-vinylpyridine) Block Copolymers

Controlling the orientation of nanostructured block copolymer (BCP) thin films is essential for their use in templating, transport, and pattern transfer. Conventional efforts mainly focus on adjusting enthalpic interactions between the blocks and interfaces, while entropic contributions are often overlooked. Here, we show that the morphology of BCP thin films can be precisely tuned by the architectural design of star BCPs. Specifically, we synthesized multiarm star BCPs with a polystyrene (PS) core and poly(2-vinylpyridine) (P2VP) corona, which exhibits a lamellar microdomain morphology. The entropic penalty associated with a parallel orientation of the microdomains to the substrate is controlled by varying the number of arms comprising the star BCPs, from 2-arms (triblock) to 3-arms and 4-arms. We systematically investigated the thin film morphology at different depths using grazing incidence small-angle X-ray and neutron scattering (GISAXS and GISANS), atomic force microscopy (AFM), water contact angle (WCA), and interference microscopy. The results show that 2-arm star BCPs show a parallel orientation, the 3-arm star BCPs form a uniform PS film at the air surface with a vertical orientation of the microdomains underneath, and the 4-arm star BCPs exhibit a parallel microdomain orientation at the air surface with mixed parallel and perpendicular microdomain orientation in the bulk. Additionally, we found that the inclination angle of microdomains at the edges of islands and holes, resulting from the incommensurability between film thickness and the characteristic period of the microdomain morphology, increases with a higher number of arms. This suggests a greater grain boundary tilt angle in the microdomains of star-shaped block copolymers (BCPs). When silicon substrates were modified with PS homopolymer, the selective interaction between substrate and core blocks promotes a parallel orientation for the 4-arm star BCPs. In conclusion, this work shows that control of arm number in star BCPs affords diverse BCP thin film morphologies, offering insights into the star BCP conformations in thin films across different depths.

36 MATERIALS SCIENCE↗
DOE OSTI2020

An All-Ceramic, Anisotropic, and Flexible Aerogel Insulation Material

To exploit the high-temperature superinsulation potential of anisotropic thermal management materials, the incorporation of ceramic aerogel into the aligned structural networks is indispensable. Yet, the long-standing obstacle to exploring ultralight superinsulation ceramic aerogels is the inaccessibility of its mechanical elasticity, stability, and anisotropic thermal insulation. Here, we report a recoverable, flexible ceramic fiber-aerogel composite with anisotropic lamellar structure, where the interfacial cross-linking between ceramic fiber and aerogel is important in its superinsulation performance. The resulting ultralight aerogel composite exhibits a density of 0.05 g/cm 3 , large strain recovery (over 50%), and low thermal conductivity (0.0224 W m –1 K –1 ), while its hydrophobicity is achieved by in situ trichlorosilane coating with the water contact angle of 135°. The hygroscopic tests of such aerogel composites demonstrate a reversible thermal insulation. The mechanical elasticity and stability of the anisotropic composites, with its soundproof performance, shed light on the low-cost superelastic aerogel manufacturing with scalability for energy saving building applications.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Achieving Flat-on Primary Crystals by Nanoconfined Crystallization in High-Temperature Polycarbonate/Poly(vinylidene fluoride) Multilayer Films and Its Effect on Dielectric Insulation

To meet the stringent requirements of next-generation film capacitors for power electronics, multilayer films (MLFs) are fabricated with the advantage of achieving high temperature rating, high energy density, and reasonably low loss simultaneously. In this study, a high permittivity polar polymer, poly(vinylidene fluoride) (PVDF), is multilayered with a linear, low loss dielectric polymer such as high-temperature polycarbonate (HTPC). However, the dielectric loss of these MLFs was still high as compared with current state-of-the-art biaxially oriented polypropylene (BOPP) films. The goal of this work is to decrease the dielectric loss and enhance dielectric insulation by achieving flat-on primary PVDF crystals in MLFs via nanoconfined melt-recrystallization. Based on simultaneous small- and wide-angle X-ray scattering experiments, edge-on lamellar crystals were observed for all as-extruded MLFs, regardless of different PVDF layer thicknesses. However, after melting at 180 °C followed by recrystallization, flat-on primary crystals were successfully achieved when the PVDF layer thickness was below 39 nm. Above 78 nm for the PVDF layer, major edge-on primary crystals with minor flat-on secondary crystals were observed. Furthermore, from leakage current, breakdown, lifetime, and electric displacement-electric field loop studies, MLFs with the flat-on primary crystals exhibited reduced loss and enhanced dielectric insulation as compared to as-extruded MLFs and those with edge-on primary/flat-on secondary crystals. This was attributed to the effective blockage of charge carriers by the flat-on PVDF primary crystals and their reduced ferroelectric switching.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Dynamic Structure and Phase Behavior of a Block Copolymer Electrolyte under dc Polarization

There is an important consideration when designing lithium battery electrolytes for advanced applications is how the electrolyte facilitates ion transport at fast charge and discharge rates. Large current densities are accompanied by large salt concentration gradients across the electrolyte. Nanostructured composite electrolytes have been proposed to enable the use of high energy density lithium metal anodes, but many questions about the interplay between the electrolyte morphology and the salt concentration gradient that forms under dc polarization remain unanswered. To address these questions, we use an in situ small-angle X-ray scattering technique to examine the nanostructure of a polystyrene- block -poly(ethylene oxide) copolymer electrolyte under dc polarization with spatial and temporal resolution. In the quiescent state, the electrolyte exhibits a lamellar morphology. The passage of ionic current in a lithium symmetric cell leads to the formation of concurrent phases: a disordered morphology near the negative electrode, lamellae in the center of the cell, and coexisting lamellae and gyroid near the positive electrode. The most surprising result of this study was obtained after the applied electric field was turned off: a current-induced gyroid phase grows in volume for 6 h in spite of the absence of an obvious driving force. We show that this reflects the formation of localized pockets of salt-dense electrolyte, termed concentration hotspots, under dc polarization. Our methods may be applied to understand the dynamic structure of composite electrolytes at appreciable current densities.

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

Fluorescence Enhancement of Lignin-Based Carbon Quantum Dots by Concentration-Dependent and Electron-Donating Substituent Synergy and Their Cell Imaging Applications

Black liquor is an important pollutant in the pulp industry, but it also has the potential for high-value utilization. In this study, lignin extracted from black liquor was hydrothermally prepared into lignin-based carbon quantum dots (L-CQDs) using a one-pot method. Physicochemical characterization suggested that the L-CQDs exhibited a lamellar core–shell multilayered graphene structure surrounded by oxygen-containing functional groups. Here, the fluorescence intensity of the L-CQDs was strengthened depending on their own concentration dependence and the doping of external groups. The fluorescence intensity of L-CQDs varied between 89.09 and 183.66 under different concentrations, and the most intense fluorescence (183.66) was obtained at 0.1 mg mL –1 . At hydroxyl and amino adsorption capacities of 11.08 and 0.98 mmol g –1 , the hydroxylated RL-CQDs-5 and aminated NL-CQDs-3 exhibited the highest fluorescence intensities at 689.22 and 605.39, respectively. Moreover, when pristine L-CQDs were sequentially aminated and hydroxylated, the NRL-CQDs’ fluorescence intensity reached 1224.92. Cell imaging experiments proved that cells cultivated with NRL-CQDs have brighter fluorescence compared with L-CQDs. The results will render L-CQDs more suitable for practical applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗