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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

In-Silico Design of Next Generation Cellulose-Derived Packaging Materials (CRADA Final Report)

Developing sustainable solutions for single-use packaging is an important objective to combat the environmental crisis of plastics pollution. Most embodiments of cellulose-based packaging materials, including CellophaneTM, are completely biodegradable in both terrestrial and marine environments. However, petroleum-derived alternatives offer some performance advantages for metrics such as moisture barriers and mechanical properties. This project leverages molecular dynamics simulation to investigate how molecular modifications to cellulose-based polymer assemblies impact their material properties. An important performance criterion for the modified materials was to retain biodegradability; thus, modifications by naturally occurring, biodegradable additives were the focus of this study. Specifically, we developed models with xylan and lignin of varying monomeric compositions into the cellulose matrix. The mechanical properties were investigated by performing stress-strain simulations, and the water barrier and hydrophobicity were investigated by simulating the water contact angle. Our findings indicate that the incorporation of xylan into the cellulose matrix tends to increase the mechanical properties with an optimal loading of ~27 wt%. We also predict that orienting the nanoscale directionality of the xylan chains such that they are perpendicular to the cellulose fibrils will dramatically increase mechanical strength. In contrast, the incorporation of lignin tends to weaken the composite at all loadings investigated. Simulations of water contact angle predicted that coating polymers on the surface of the cellulose assembly creates a more hydrophobic surface than incorporating them throughout the matrix. Of the coatings investigated, lignin resulted in the most hydrophobic surface, followed by pectin and keratin, which both imparted modest increases in hydrophobicity. Future experimental work done by Futamura will focus on designing material prototypes to capitalize on the predictions of performance enhancement obtained from molecular modeling. While substantial progress was made by the simulations performed in this project, there still exists a vast parameter space that we were unable to investigate, including branching, functional group decoration, and degree of polymerization of polymer additives. However, the methods developed in this initial investigation will facilitate more rapid evaluation of the impact of molecular characteristics on the performance of biopolymer composite materials and thereby accelerate future materials discovery efforts in this area.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Cleaning and dewatering fine coal

Fine coal is cleaned of its mineral matter impurities and dewatered by mixing the aqueous slurry containing both with a hydrophobic liquid, subjecting the mixture to a phase separation. The resulting hydrophobic liquid phase contains coal particles free of surface moisture and droplets of water stabilized by coal particles, while the aqueous phase contains the mineral matter. By separating the entrained water droplets from the coal particles mechanically, a clean coal product of substantially reduced mineral matter and moisture contents is obtained. The spent hydrophobic liquid is separated from the clean coal product and recycled. The process can also be used to separate one type of hydrophilic particles from another by selectively hydrophobizing one.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2025

Silylsilane‐Substituted Polymers: Fluorine‐Free, Liquid Repellent, and Hydrolytically Stable Alternatives to Siloxanes

Abstract Per‐ and polyfluoroalkyl substances (PFAS) are omniphobic and exceptionally stable, making them ideal for a wide range of materials applications. However, as “forever chemicals”, their exceptional persistence and bioaccumulation have generated an increasing amount of environmental and health concerns, prompting the search for fluorine‐free alternatives. Siloxane‐based materials are therefore interesting to examine as PFAS alternatives due to their low surface energy and hydrophobicity but suffer from hydrolytic instability of Si─O linkages. To address this challenge, a novel methacrylate monomer, 3‐[tris(trimethylsilyl)silyl]propyl methacrylate (M‐silyl), is designed containing Si─Si bonds rather than Si─O bonds of siloxanes. Polymers derived from M‐silyl (P‐silyl) is prepared by controlled free radical polymerization and compared with their siloxane analogues after coating on silicon wafers. Contact angle (CA) measurements confirmed P‐silyl to be hydrophobic (advancing/receding water CA = 109.7°/83.0°), with a low‐hysteresis for oil (lyophobic) (hexadecane CA hysteresis = 2.0°), comparable to its siloxane‐based counterpart. Importantly, P‐silyl maintained these surface properties after exposure to acidic or basic conditions, while siloxane analogues lost hydrophobicity. Consequently, the incorporation of Si ─ Si linkages into the design of the polymer enables chemically stable, fluorine‐free alternatives for water‐repellent and low hysteresis surface coatings and advances the design of fluorine‐free functional materials.

fluorine-free↗
DOE OSTI2020

Composite Structured Surfaces for Durable Dropwise Condensation

Dropwise condensation of steam on hydrophobic substrates has a 10X higher heat transfer coefficient compared to filmwise condensation. To promote dropwise condensation, low surface energy hydrophobic coatings (polymers) are typically utilized. The low intrinsic thermal conductivity (k < 1 W/(m · K)) of polymers, coupled with high heat transfer coefficient of dropwise condensation (100 kW/(m 2 · K)), necessitates that the coating be thin (< 1µm) in order to avoid reducing the overall heat exchanger conductance. However, thin polymeric films easily degrade. The two opposing requirements result in the need for optimization between the durability (thick coating) and the heat transfer (thin coating). To enable high thermal conductivity in thicker coatings, we develop metal-polymer structured surfaces. By using porous structures as inter-connected heat-conducting backbones that are filled with hydrophobic materials, we enable tuning of the coating effective thermal conductivity and surface energy. Three metal structures were studied; micro/nanowires, inverse opals, and sintered spheres. Heat transfer performance was calculated using three-dimensional finite element method simulations with two distinct boundary conditions; convection at the walls and isothermal walls. Interestingly, the overall conductance shows up to 40% difference depending on the boundary condition used in calculating the composite coating effective thermal conductivity. We use our model to predict the heat transfer performance as a function of metal fraction by volume and by surface area for condensation. By coupling our thermal simulations with a previously verified analytical model for predicting wetting behavior on heterogeneous surfaces, we propose a regime map to predict dropwise-to-filmwise transition. Furthermore, our work not only forms a starting point for the development of durable dropwise condensing surfaces, it identifies important considerations needed for computing effective thermal conductivity of composites.

42 ENGINEERING↗
DOE OSTI2021

Partitioning of Seven Different Classes of Antibiotics into LPS Monolayers Supports Three Different Permeation Mechanisms through the Outer Bacterial Membrane

The outer membrane (OM) of Gram-negative (G-) bacteria presents a barrier for x classes of antibacterial agents. Lipopolysaccharide (LPS), present in the outer leaflet of the OM, is stabilized by divalent cations and is considered to be the major impediment for antibacterial agent permeation. However, the actual affinities of major antibiotic classes toward LPS have not yet been determined. In the present work, we use Langmuir monolayers formed from E. coli Re and Rd types of LPS to record pressure-area isotherms in the presence of antimicrobial agents. Our observations suggest three general types of interactions. Firstly, some antimicrobials demonstrated no measurable interactions with LPS. This lack of interaction in the case of cefsulodin, a third-generation cephalosporin antibiotic, correlates with its low efficacy against G- bacteria. Ampicillin and ciprofloxacin also show no interactions with LPS, but in contrast to cefsulodin, both exhibit good efficacy against G- bacteria, indicating permeation through common porins. Secondly, we observe substantial intercalation of the more hydrophobic antibiotics novobiocin, rifampicin, azithromycin, and telithromycin into relaxed LPS monolayers. These largely re-partition back to the subphase with monolayer compression. We find that the hydrophobic area, charge, and dipole all show correlations with both the mole fraction of antibiotic retained in the monolayer at the monolayer-bilayer equivalence pressure and the efficacies of these antibiotics against G- bacteria. Thirdly, amine-rich gentamicin and the cationic antimicrobial peptides polymyxin B and colistin show no hydrophobic insertion but are instead strongly driven into the polar LPS layer by electrostatic interactions in a pressure-independent manner. Their intercalation stably increases the area per molecule (by up to 20%), which indicates massive formation of defects in the LPS layer. These defects support a self-promoted permeation mechanism of these antibiotics through the OM, which explains the high efficacy and specificity of these antimicrobials against G- bacteria.

lateral pressure↗
DOE OSTI2024

Long-Chain Lipids Facilitate Insertion of Large Nanoparticles into Membranes of Small Unilamellar Vesicles

Insertion of hydrophobic nanoparticles into phospholipid bilayers is limited to small particles that can incorporate into a hydrophobic membrane core between two lipid leaflets. Incorporation of nanoparticles above this size limit requires the development of challenging surface engineering methodologies. In principle, increasing the long-chain lipid component in the lipid mixture should facilitate incorporation of larger nanoparticles. Here, we explore the effect of incorporating very long phospholipids (C24:1) into small unilamellar vesicles on the membrane insertion efficiency of hydrophobic nanoparticles that are 5–11 nm in diameter. To this end, we improve an existing vesicle preparation protocol and utilized cryogenic electron microscopy imaging to examine the mode of interaction and evaluate the insertion efficiency of membrane-inserted nanoparticles. We also perform classical coarse-grained molecular dynamics simulations to identify changes in lipid membrane structural properties that may increase insertion efficiency. Furthermore, our results indicate that long-chain lipids increase the insertion efficiency by preferentially accumulating near membrane-inserted nanoparticles to reduce the thermodynamically unfavorable disruption of the membrane.

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

Design and synthesis of biobased superhydrophobic biochar catalyst derived from Citrus sinensis for biodiesel production using inedible oil feedstocks

In an one-pot in situ trans/esterification of low-grade feedstocks, the simultaneous presence of triglycerides (TAGs) and free fatty acids (FFAs) presents a dual catalytic challenge. While TAGs undergo transesterification to form biodiesel and glycerol, FFAs present in the feedstocks are esterified simultaneously, producing water as a by-product. This water can deactivate acid catalysts by interacting with their active sites, reducing catalytic efficiency and reusability. To overcome this, we developed a hydrophobic sulfonic acid-functionalized biochar catalyst derived from Citrus sinensis (orange peel) via sulfonation with H 2 SO 4 and subsequent silylation using hexamethyldisilazane (HMDS). The optimized catalyst exhibited a high surface area (355.09 m 2 g −1 ), sulfur content (5.33 wt%), and strong hydrophobicity (water contact angle: 154°). Compared to non-hydrophobic analogs, it showed enhanced activity and reusability (up to 10 cycles). Using response surface methodology with central composite design, a biodiesel yield of 99.1 ± 0.4% was achieved under optimal conditions. Life cycle assessment was performed to evaluate the environmental impacts of biodiesel production utilising the synthesized catalyst, considering 1000 kg of biodiesel produced as 1 functional unit. In conclusion, the recorded results showed the cumulative abiotic depletion of fossil resources over the entire biodiesel production process as 87 243.423 MJ and global warming potential as 4103.494 kg CO 2 equivalent.

Biochar↗
DOE OSTI2022

On the mechanisms of ion adsorption to aqueous interfaces: air-water vs. oil-water

The adsorption of ions to water-hydrophobe interfaces influences a wide range of phenomena, including chemical reaction rates, ion transport across biological membranes, and electrochemical and many catalytic processes; hence, developing a detailed understanding of the behavior of ions at water-hydrophobe interfaces is of central interest. Here, we characterize the adsorption of the chaotropic thiocyanate anion (SCN − ) to two prototypical liquid hydrophobic surfaces, water-toluene and water-decane, by surface-sensitive nonlinear spectroscopy and compare the results against our previous studies of SCN − adsorption to the air-water interface. For these systems, we observe no spectral shift in the charge transfer to solvent spectrum of SCN − , and the Gibb’s free energies of adsorption for these three different interfaces all agree within error. We employed molecular dynamics simulations to develop a molecular-level understanding of the adsorption mechanism and found that the adsorption for SCN − to both water-toluene and water-decane interfaces is driven by an increase in entropy, with very little enthalpic contribution. This is a qualitatively different mechanism than reported for SCN − adsorption to the air-water and graphene-water interfaces, wherein a favorable enthalpy change was the main driving force, against an unfavorable entropy change.

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

Mitigation of Leakage and Water Ingress for a Promising Phase Change Material (PCM) Containing Polyethylene Glycol (PEG)

A promising and cost-effective phase change material (PCM) containing polyethylene glycol (PEG) 600, 800, and/or 1000 has been synthesized. It is shape stabilized using a sol-gel method and displays promising thermal properties. These properties make the PCMs good candidates for thermal batteries and other thermal energy storage applications in the building sector. However, PEG leakage is observed at elevated temperatures, and due to the hygroscopic nature of PEG, moisture ingress is also observed, which can have a significant effect on performance and durability. Thus, we have developed hydrophobic coatings to prevent PEG leakage and mitigate moisture ingress. The selected approach involves a secondary sol-gel process during which a thin layer formulated with hydrophobic precursors is deposited onto the surface of the PCM samples. Several coating formulations have been investigated, including formulations composed of tetraethyl orthosilicate (TEOS), diethoxy(dimethyl)silane (DEDMS), triethoxymethylsilane (TEMS), and n-octyltriethoxysilane (OTES). We find that this is effective at increasing hydrophobicity of the PCM substrates. It also decreases substrate leakage.

ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION↗
DOE OSTI2021

AFM Slip Length Measurements for Water at Selected Phyllosilicate Surfaces

Most reported slip length measurements have been made at the surfaces of synthetic materials and modified synthetic materials. In contrast, few slip length measurements at the surface of unmodified natural mineral surfaces have been reported. In this regard, flow at the silica face surfaces of the phyllosilicate minerals, talc and mica, was considered. A slip boundary condition was expected at the nonpolar hydrophobic silica surface of talc leading to enhanced flow, and a no-slip boundary condition was expected at the hydrophilic silica surface of mica. Atomic force microscopy (AFM) slip length measurements were made at the talc and mica surfaces. The slip length results for the hydrophobic silica surface of talc were contrasted to the results for the hydrophilic silica surface of mica (no-slip flow). The results are discussed based on molecular dynamics simulations (MDS), as reported in the literature, and AFM images of surface nanobubbles. For nonpolar hydrophobic surfaces (such as talc), it is doubtful that the MDS interfacial water structure and the water exclusion zone (3.2 Å) account for the AFM slip flow with slip lengths as great as 95 nm. Rather, a better explanation for the AFM slip flow condition is based on reduced interfacial viscosity due to the presence of dissolved gas and the accommodation of pancake nanobubbles at the talc surface having a height dimension of magnitude similar to the slip length.

42 ENGINEERING↗
DOE OSTI2022

Mitigation of Leakage and Water Ingress for a Promising Phase Change Material (PCM) Containing Polythylene Glycol (PEG): Preprint

A promising and cost-effective phase change material (PCM) containing polyethylene glycol (PEG) 600, 800, and/or 1000 has been synthesized. It is shape stabilized using a sol-gel method and displays promising thermal properties. These properties make the PCMs good candidates for thermal batteries and other thermal energy storage applications in the building sector. However, PEG leakage is observed at elevated temperatures, and due to the hygroscopic nature of PEG, moisture ingress is also observed, which can have a significant effect on performance and durability. Thus, we have developed hydrophobic coatings to prevent PEG leakage and mitigate moisture ingress. The selected approach involves a secondary sol-gel process during which a thin layer formulated with hydrophobic precursors is deposited onto the surface of the PCM samples. Several coating formulations have been investigated, including formulations composed of tetraethyl orthosilicate (TEOS), diethoxy(dimethyl)silane (DEDMS), triethoxymethylsilane (TEMS), and n- octyltriethoxysilane (OTES). We find that this is effective at increasing hydrophobicity of the PCM substrates. It also decreases substrate leakage.

ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION↗
DOE OSTI2020

Optimization of fluorescence and surface adsorption of citric acid/ethanolamine carbon nanoparticles for subsurface tracers

The tunable fluorescence and biocompatibility of fluorescent carbon nanoparticles (FCNs) makes them appealing tracers in geothermal, environmental, and clinical applications. Here, we address FCNs synthesized from reaction and pyrolysis of citric acid and ethanolamine. We examine the fluorescence and the adsorption of these FCNs as critical parameters that influence their use in applications. FCN fluorescence was observed to develop during pyrolysis and measured at pyrolysis temperatures ranging from 190 to 250 °C. Transmission electron microscopy shows that the FCN average diameter of approximately 13 nm is unaffected by pyrolysis temperature. However, pyrolysis temperature strongly affects fluorescence, which peaks at 210 °C. Here, the surface hydrophobicity of the FCNs increases with pyrolysis temperature as measured by retention on reverse phase chromatography. Together, these results suggest that particle surface functionalities provide both fluorescence and hydrophilicity, and that these surface functionalities are destroyed with excessive pyrolysis. To examine their surface adsorption, quartz crystal microbalance measurements demonstrate that pyrolysis temperature increases FCN adsorption on mineral surfaces. Surfaces with greater hydrophobicity show greater FCN adsorption. Adsorption is unaffected by the presence of mono- or divalent ions in solution. This suggests adsorption by hydrophobic interaction for the Fe 2 O 3 , SiO 2 , and AlSiO surfaces studied.

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

Understanding Self-Assembly and the Stabilization of Liquid/Liquid Interfaces: The Importance of Ligand Tail Branching and Oil-Phase Solvation

Organophosphorus-based ligands represent a versatile set of solvent extraction reagents whose chemical makeup plays an important role in extraction mechanism. We hypothesize that the branching of the extractant hydrophobic tail and its oil-phase solvation affect the liquid/liquid interfacial structure. Understanding the structure mediated adsorption and interfacial ordering becomes key in designing ligands with enhanced selectivity and efficiency for targeted extractions. We employed vibrational sum frequency generation spectroscopy and interfacial tension measurements to extract thermodynamic adsorption energies, map interfacial ordering, and rationalize disparate behaviors of model di-(2-ethylhexyl) phosphoric acid and dioctyl phosphoric acid ligands at the hexadecane water interface. With increased surface loading, ligands with branched hydrophobic tails formed stable interfaces at much lower concentrations than those observed for ligands with linear alkyl tails. The lack of an oil phase and associated solvation results in markedly different interfacial properties, and thus measurements made at air/liquid surfaces cannot be assumed to correlate with the processes occurring at buried liquid/liquid interfaces. Here, we attribute these differences in the surface mediated self-assembly to key variations in hydrophobic interactions and tail solvation taking place in the oil phase demonstrating that interactions in both the polar and nonpolar phases are essential to understand self-assembly and function.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Formation of carbon and oxygen rich surface layer on high purity magnesium by atmospheric carbon dioxide plasma

Carbon and oxygen-rich corrosion barrier layer formed on Mg by a simple and scalable CO 2 atmospheric plasma (CO 2 -AP) process. The reactive CO 2 -AP interacts with the Mg surface and forms a unique layered structure with the top MgCO 3 /MgO-intermixed particulates pillars and the bottom dense layer. The surface features were simultaneously formed on the nano-/micro-structured MgO layer by carbonate molecules, plasma-active CO 2 molecules, and/or other volatile organic compounds on the nano-/micro-structured MgO particle layer. The resulting surfaces after CO 2 -AP were either hydrophobic or hydrophilic and exhibited lower anodic current or high resistance for Mg corrosion. For the hydrophobic surfaces of CO 2 -AP treated Mg, molecular dynamic simulations were performed to understand the origin of hydrophobicity and identified that the amorphous carbon layers formed on the Mg surface are the source. The environmentally benign abundant-gas-based process enables the cost reduction associated with waste treatment, generation of by-product, and supply of raw material.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Structure and Interactions of HIV-1 gp41 CHR-NHR Reverse Hairpin Constructs Reveal Molecular Determinants of Antiviral Activity

Engineered reverse hairpin constructs containing a partial C-heptad repeat (CHR) sequence followed by a short loop and full-length N-heptad repeat (NHR) were previously shown to form trimers in solution and to be nanomolar inhibitors of HIV-1 Env mediated fusion. Their target is the in situ gp41 fusion intermediate, and they have similar potency to other previously reported NHR trimers. However, their design implies that the NHR is partially covered by CHR, which would be expected to limit potency. An exposed hydrophobic pocket in the folded structure may be sufficient to confer the observed potency, or they may exist in a partially unfolded state exposing full length NHR. Here, in this study, we examined their structure by crystallography, CD and fluorescence, establishing that the proteins are folded hairpins both in crystal form and in solution. We examined unfolding in the milieu of the fusion reaction by conducting experiments in the presence of a membrane mimetic solvent and by engineering a disulfide bond into the structure to prevent partial unfolding. We further examined the role of the hydrophobic pocket, using a hairpin-small molecule adduct that occluded the pocket, as confirmed by X-ray footprinting. The results demonstrated that the NHR region nominally covered by CHR in the engineered constructs and the hydrophobic pocket region that is exposed by design were both essential for nanomolar potency and that interaction with membrane is likely to play a role in promoting the required inhibitor structure. The design concepts can be applied to other Class 1 viral fusion proteins.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Durable and Highly Selective Ion Transport of a Sulfonated Diels Alder Poly(phenylene) for Vanadium Redox Flow Batteries

In order to improve the durability and ion selectivity of a hydrocarbon membrane for vanadium redox flow batteries (VRFBs) a polymer was rationally designed with an external hydrophobic shell and internal hydrophilic core. The polymer was designed to prevent hydrophilic polymer chain aggregation by functionalizing the external polymer shell with hydrophobic side chains and attaching acid moieties onto the polymer backbone. The hydrophobic shell is the result of pentafluorobenzoyl group functionalization on the pendent aryl rings in a Diels Alder poly(phenylene) backbone. The internal polymer chain contains sulfonic acid moieties to impart hydrophilic character. The physical and electrochemical characteristics of the membrane were systematically studied and compared with widely used Nafion-212. The synthesized membranes were found to be superior to Nafion-212 not only in terms of lower vanadium ion permeability (4.25 x 10 -8 vs. Nafion-212: 6.0 x 10 -6 cm 2 min -1 ) but also in higher VRFB performance (EE = 89% and vs. Nafion-212: 85.5% at 40 mA/cm 2 ). The membrane also showed over three times higher capacity retention than Nafion-212 (0.075 % vs. 0.25 % capacity loss per cycle respectively) and excellent ex situ and in situ chemical stability.

25 ENERGY STORAGE↗
DOE OSTI2021

Efficient production of oxidized terpenoids via engineering fusion proteins of terpene synthase and cytochrome P450

The functionalization of terpenes using cytochrome P450 enzymes is a versatile route to the production of useful derivatives that can be further converted to value-added products. Many terpenes are hydrophobic and volatile making their availability as a substrate for P450 enzymes significantly limited during microbial production. In this study, we developed a strategy to improve the accessibility of terpene molecules for the P450 reaction by linking terpene synthase and P450 together. As a model system, fusion proteins of 1,8-cineole synthase (CS) and P450 cin were investigated and it showed an improved hydroxylation of the monoterpenoid 1,8-cineole up to 5.4-fold. Structural analysis of the CS-P450 cin fusion proteins by SEC-SAXS indicated a dimer formation with preferred orientations of the active sites of the two domains. We also applied the enzyme fusion strategy to the oxidation of a sesquiterpene epi-isozizaene and the fusion enzymes significantly improved albaflavenol production in engineered E. coli. From the analysis of positive and negative examples of the fusion strategy, we proposed key factors in structure-based prediction and evaluation of fusion enzymes. Developing fusion enzymes for terpene synthase and P450 presents an efficient strategy toward oxidation of hydrophobic terpene compounds. This strategy could be widely applicable to improve the biosynthetic titer of the functionalized products from hydrophobic terpene intermediates.

59 BASIC BIOLOGICAL SCIENCES↗