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All sources NASA NTRS DOE OSTI

DOE OSTI2022

Piezoelectric property of PZT nanofibers characterized by resonant piezo-force microscopy

Nano-piezoelectric materials have drawn tremendous research interest. However, characterization of their piezoelectric properties, especially measuring the piezoelectric strain coefficients, remains a challenge. Normally, researchers use an AFM-based method to directly measure nano-materials’ piezoelectric strain coefficients. But, the extremely small piezoelectric deformation, the influence from the parasitic electrostatic force, and the environmental noise make the measurement results questionable. In this paper, a resonant piezo-force microscopy method was used to accurately measure the piezoelectric deformation from 1D piezoelectric nanofibers. During the experiment, the AFM tip was brought into contact with the piezoelectric sample and set to work at close to its first resonant frequency. A lock-in amplifier was used to pick up the sample’s deformation signal at the testing frequency. By using this technique, the piezoelectric strain constant d 33 of the Lead Zirconate Titanate (PZT) nanofiber with a diameter of 76 nm was measured. The result showed that d 33 of this PZT nanofiber was around 387 pm/V. Meanwhile, by tracking the piezoelectric deformation phase image, domain structures inside PZT nanofibers were identified.

36 MATERIALS SCIENCE↗

DOE OSTI2020

3D Hybrid Nanofiber Aerogels Combining with Nanoparticles Made of a Biocleavable and Targeting Polycation and MiR‐26a for Bone Repair

Abstract The healing of large bone defects represents a clinical challenge, often requiring some form of grafting. 3D nanofiber aerogels could be a promising bone graft due to their biomimetic morphology and controlled porous structures and composition. miR‐26a has been reported to induce the differentiation of bone marrow‐derived mesenchymal stem cells (BMSCs) and facilitate bone formation. Introducing miR‐26a with a suitable polymeric vector targeting BMSCs could improve and enhance the functions of 3D nanofiber aerogels for bone regeneration. Herein, the comb‐shaped polycation (HA–SS–PGEA) is first developed, carrying a targeting component, biocleavable groups, and short ethanolamine (EA)‐decorated poly(glycidyl methacrylate) (PGMA) (abbreviated as PGEA) arms as miR‐26a delivery vector. Thereafter, the cytotoxicity and transfection efficiency of this polycation and cellular response to miR‐26a‐incorporated nanoparticles (NPs) are assessed in vitro. HA–SS–PGEA exhibits a stronger ability to transport miR‐26a and exert its functions than the gold standard polyethyleneimine (PEI) and low‐molecular‐weight linear PGEA. The efficacy of HA–SS–PGEA/miR‐26a NPs loaded 3D hybrid nanofiber aerogels showing a positive effect on the cranial bone defect healing is finally examined. Together, the combination of 3D nanofiber aerogels and functional NPs consisting of a biodegradable and targeting polycation and therapeutic miRNA could be a promising approach for bone regeneration.

Li, Ruiquan↗

DOE OSTI2023

Sequence-dependent self-assembly of supramolecular nanofibers in periodic dynamic block copolymers

Block copolymers (BCPs) can spontaneously self-assemble into various nanostructured morphologies which enable their diverse applications in selective membranes, polymer electrolytes, and optoelectronics. To expand the range of nanostructures accessible to block copolymers, we designed dynamic block copolymers (DBCPs) that combine the phase separation of traditional block copolymers with the supramolecular self-assembly of periodic dynamic polymers. We demonstrate that DBCPs synthesized with a periodic block sequence self-assemble into high aspect ratio supramolecular nanofibers with well-ordered PEG and PDMS domains, in contrast to those synthesized with a random sequence which do not form nanofibers but have disordered morphologies. The periodicity of the block sequence ensures regular placement of dynamic bonds along the polymer chain, which enables stacking of the hydrogen bonding units into ordered 1D supramolecular nanofibers and delays the onset of terminal flow by up to 60 °C compared to the random block sequence. The hierarchically assembled supramolecular nanofibers display complex mechanical and thermal phase behavior arising from the interplay between phase separation of the dissimilar polymer backbones and supramolecular interactions between dynamic bonds. Despite identical bulk composition, the periodic DBCPs demonstrate ionic conductivity values over two orders of magnitude higher than their random counterparts due to the formation of well-ordered, interconnected, high aspect ratio ion-transporting PEG domains. In conclusion, these results highlight the potential for DBCPs as an emerging material platform to achieve advanced, self-assembled nanostructured morphologies.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Improved Water Management of Electrospun Nanofiber Membrane Electrode Assemblies at High Current Densities Measured in Operando Using Neutron Radiography

Neutron radiography was used to measure water concentrations through the cross-sections of sprayed gas diffusion electrodes (GDE) and electrospun perfluorosulfonic acid-platinum nanofiber (NF) electrodes during fuel cell operation. The performance of Generation 1 poly(acrylic acid)-based NF electrodes is improved at high current densities compared to the baseline given by a GDE cell. Through-thickness water profiles reveal that at high current densities, the water concentrations within the membrane electrode assembly (MEA) and gas diffusion layers are around 2x lower in the nanofiber-containing MEA compared to the baseline GDE, commensurate with the observed polarization performance. In Generation 2 electrospun nanofiber electrodes, poly(ethylene oxide)-based electrodes show higher performance than poly(acrylic acid) electrodes, while retaining less water in the MEA. Furthermore, these results imply that the electrospun nanofiber electrodes have an improved ability to maintain hydration without flooding, which leads to improved performance over a range of relative humidities.

42 ENGINEERING↗

DOE OSTI2023

Compact scalable nanofiber mass production using electrospinning

A low power out put high voltage power supply unit for mass producing thicker nanofiber mat has been built in-house and earned a provisional patent last year. This nanofiber fabrication unit has unique features to produce stand alone thick ceramic nanofiber for specialized application such as isotop production and accelerator targets for high energy physics experiments. This is a versatile unit which can produce wide variety of polymer nanofibers on a semi industrial scale for application in air filtration, face mask, facial beauty pads, gas sensors and many more.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2019

Co-Continuous Phase Nanofiber Composites

We report on the development of a co-continuous phase composite with a polyacrylonitrile (PAN nanofiber network integrated into an acrylonitrile-butadiene-styrene (ABS) matrix that offers improved mechanical strength. Homogeneous dispersion of nanomaterials in a matrix can be challenging and typically involves mechanical mixing or chemical modification. This work overcomes this obstacle by taking an inverse approach in that a nanoscale network is synthesized then infiltrated with polymer instead of attempting to disperse the nanomaterial in the polymer. This not only enables excellent homogeneity but also allows the nanoscale phase to be continuous throughout the composite. Here, PAN is electrospun to form a random network of nanofibers having diameters of roughly 200 nm, which is then infiltrated with ABS using solution processing. By optimizing the heat treatments and ABS concentrations, the tensile strength and elastic modulus were improved by 208% and 313%, respectively, as compared to the bare PAN nanofibers. Since there has been significant previous research efforts on electrospinning polymers, many different nanofiber and polymer systems can be made into composites using the methodology established in this work. Therefore, this research offers a new route to create a co-continuous composite with the aim to replace some existing fiber reinforced composites.

Bowland, Christopher↗

DOE OSTI2022

Acid-Base Equilibrium and Dielectric Environment Regulate Charge in Supramolecular Nanofibers

Peptide amphiphiles are a class of molecules that can self-assemble into a variety of supramolecular structures, including high-aspect-ratio nanofibers. It is challenging to model and predict the charges in these supramolecular nanofibers because the ionization state of the peptides are not fixed but liable to change due to the acid-base equilibrium that is coupled to the structural organization of the peptide amphiphile molecules. Here, we have developed a theoretical model to describe and predict the amount of charge found on self-assembled peptide amphiphiles as a function of pH and ion concentration. In particular, we computed the amount of charge of peptide amphiphiles nanofibers with the sequence C 16 − V 2 A 2 E 2 . In our theoretical formulation, we consider charge regulation of the carboxylic acid groups, which involves the acid-base chemical equilibrium of the glutamic acid residues and the possibility of ion condensation. The charge regulation is coupled with the local dielectric environment by allowing for a varying dielectric constant that also includes a position-dependent electrostatic solvation energy for the charged species. We find that the charges on the glutamic acid residues of the peptide amphiphile nanofiber are much lower than the same functional group in aqueous solution. There is a strong coupling between the charging via the acid-base equilibrium and the local dielectric environment. Our model predicts a much lower degree of deprotonation for a position-dependent relative dielectric constant compared to a constant dielectric background. Furthermore, the shape and size of the electrostatic potential as well as the counterion distribution are quantitatively and qualitatively different. These results indicate that an accurate model of peptide amphiphile self-assembly must take into account charge regulation of acidic groups through acid–base equilibria and ion condensation, as well as coupling to the local dielectric environment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS2002

Electrical Characterization of Polyaniline/polyethylene Oxide Nanofibers for Field Effect Transistors

Nanofibers comprised of polyaniline/polyethylene oxide (PANI/PEO) are being developed for novel logic devices. We report the electrical conductivity of PANI/PEO nanofibers with diameters in the 100 to 200 nm range. We measured conductivity values of approx. 0.3 to 1.0 S/cm, which is higher than the values reported for thicker nanofibers, but less than the bulk value of PANI. The electrical measurements were performed by depositing the fibers on pre-electroded, oxidized silicon (Si) substrates. The excellent adherence of the nanofibers to the SiO2 as well as the gold (Au) electrodes may be useful in the design of future devices.

Mueller, Carl H.↗

NASA NTRS2012

Electrospun Nanofiber Coating of Fiber Materials: A Composite Toughening Approach

Textile-based composites could significantly benefit from local toughening using nanofiber coatings. Nanofibers, thermoplastic or otherwise, can be applied to the surface of the fiber tow bundle, achieving toughening of the fiber tow contact surfaces, resulting in tougher and more damage-resistant/tolerant composite structures. The same technique could also be applied to other technologies such as tape laying, fiber placement, or filament winding operations. Other modifications to the composite properties such as thermal and electrical conductivity could be made through selection of appropriate nanofiber material. Control of the needle electric potential, precursor solution, ambient temperature, ambient humidity, airflow, etc., are used to vary the diameter and nanofiber coating morphology as needed. This method produces a product with a toughening agent applied to the fiber tow or other continuous composite precursor material where it is needed (at interfaces and boundaries) without interfering with other composite processing characteristics.

Kohlman, Lee W.↗

DOE OSTI2020

Amino acids react with carbon dioxide (CO2) and form nanofibers and nanoflowers

A method for capturing CO2 comprising dissolving at least one pure amino acid (AA) in water without the use of a catalyst for establishing protonation of an amino group of the amino acid, adding at least one base solution to the amino acid and water solution to deprotonate the protonated amino group of the amino acid and forming an amino acid-XOH—H2O wherein X is sodium or potassium, and subjecting CO2 to the amino acid-XOH—H2O to form new nanomaterials is provided. A regenerable nanofiber is disclosed comprising a NaHCO3 nanofiber, a KHCO3 nanofiber, or an amino acid nanofiber made from subjecting a CO2 gas to an amino acid aqueous solvent. Preferably, the amino acid aqueous solvent is one or more of a Gly-NaOH—H2O, an Ala-NaOH—H2O, a Phe-NaOH—H2O, a Gly-KOH—H2O, an Ala-KOH—H2O, and a Phe-KOH—H2O.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Electrospun Nanofibers

Electrospun nanofibers have been considered promising separator candidates for lithium–sulfur (Li–S) batteries due to their unique properties, including but not limited to their high surface area, superior surface-to-volume ratio, excellent flexibility, good mechanical performance, etc. This chapter aims to provide an overview of research in electrospun nanofibers with their applications in Li–S batteries. It starts with a brief introduction to Li–S batteries, followed by the principle and advantages of electrospun nanofibers performed in this area. Applications of electrospun separators in Li–S batteries have been further discussed in detail. In the end, a future vision regarding challenges and perspectives is proposed to provide insightful comments in this field. It is believed that this chapter will provide an extensive and comprehensive reference to utilize this advanced technique to generate novel nanofiber separators for next-generation Li–S batteries.

Zhu, Jiadeng↗

DOE OSTI2019

Self-assembly and metal-directed assembly of organic semiconductor aerogels and conductive carbon nanofiber aerogels with controllable nanoscale morphologies

A versatile and highly tunable synthesis for nanofiber aerogels based on the n-type organic semiconductor perylene tetracarboxylic diimide (PTCDI) is presented. PTCDI nanofiber aerogels are demonstrated to incorporate the organic semiconductor into a high surface area and porous morphology and can also be graphitized to synthesize carbon nanofiber (CNF) aerogels by thermal annealing. Using this approach, CNF aerogels with variable density and crystallinity are synthesized. Furthermore, by incorporating metal salts into the synthesis, metal-directed assembly yields a variety of nanoscale morphologies. The selection of post-synthesis thermal treatment can result in metal-directed assembly of PTCDI aerogels, low crystallinity graphitic aerogels decorated with metal nanoparticles, or highly crystalline graphitic aerogels with controllable nanoscale morphologies. The high surface area and porosity afforded by the aerogel morphology coupled with the intrinsic properties of PTCDI or CNFs is important for improving their performance in a number of applications including energy storage and catalysis.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Plasmonic gold-cellulose nanofiber aerogels

Assembly of plasmonic nanomaterials into a low refractive index medium, such as an aerogel, holds a great promise for optical metamaterials, optical sensors, and photothermal energy converters. However, conventional plasmonic aerogels are opaque and optically isotropic composites, impeding them from being used as low-loss or polarization-dependent optical materials. Here we demonstrate a plasmonic-cellulose nanofiber composite aerogel that comprises of well-dispersed gold nanorods within a cellulose nanofiber network. The cellulose aerogel host is highly transparent owing to the small scattering cross-section of the nanofibers and forms a nematic liquid crystalline medium with strong optical birefringence. We find that the longitudinal surface plasmon resonance peak of gold nanorods shows a dramatic shift when probed for the cellulose aerogel compared with the wet gels. Simulations reveal the shift of surface plasmon resonance peak with gel drying can be attributed to the change of the effective refractive index of the gels. This composite material may provide a platform for three- dimensional plasmonic devices ranging from optical sensors to metamaterials.

36 MATERIALS SCIENCE↗

DOE OSTI2026

Hybrid Bio-Based Composites: Enabling Cellulose Nanofiber (CNF) Incorporation into Composites via Macroscale Natural Fiber Carriers

Cellulose nanofibers (CNFs) have significant potential in composites as additives to improve mechanical properties, melt rheology, and more. However, agglomeration of CNFs is a key challenge in composite melt processing as obtaining nano-level dispersion of CNFs often requires cost- and energy-intensive processes (e.g., solvent exchange or freeze drying) due to the strong hornification tendencies of CNF. Herein, we avoid these challenges by using a natural fiber carrier method to integrate CNF into thermoplastic composites. Fibers are co-dried to create a hybrid fiber feedstock for compounding in which natural fibers are decorated with dispersed nanofibers. The hybridized fibers result in up to a 24% increase in tensile strength and up to a 35% increase in Young’s modulus compared to composites only containing natural fibers. The lignocellulosic nanofibers are found to outperform their purely cellulosic counterpart, which is theorized to be due to either an increased propensity for fibrillation of the lignocellulosic fibers or the increased hydrophobicity of the fibers due to the presence of lignin. Surface analysis of fiber feedstocks, via streaming potential measurements and dynamic light scattering (DLS), confirmed a significant change in the feedstock hydrophobicity before and after hybridization. While mild additions of CNF (1 wt.% on the macroscale fiber) do not impact the composite melt viscosity, the viscosity is found to increase at higher CNF loadings (5 wt.% on the macroscale fiber), indicating its utility as a rheology modifier. Lastly, use of these materials as novel feedstocks for medium-scale additive manufacturing in high-fidelity part production was demonstrated.

bio-based↗

DOE OSTI2025

Self‐Standing Carbon Nanofibers@Carbon Felt Electrodes to Boost Electrolyzer Productivity: Application to the Electro‐Manufacturing of trans ‐3‐Hexenedioic Acid and Adipic Acid

The industrial implementation of electrosynthesis for chemical manufacturing remains constrained by the limited surface area of conventional electrodes. Herein, this challenge is addressed by designing a carbon nanofiber@carbon felt (CNF@CF) electrode platform that combines the high conductivity, flexibility, and ease of handling of commercial carbon felts (CF) with the large surface area and tunable surface chemistry of carbon nanofibers (CNFs). CNFs are deliberately grown onto the CF scaffold to form a sword-in-sheath structure, where entangled nanofibers wrap the felt macrofibers to provide excellent mechanical stability and electrical conductivity without binders. CNF@CF is evaluated both as an electrode and as a catalyst support for the electrochemical hydrogenation of cis,cis-muconic acid (ccMA), a biobased platform molecule key to the production of performance polyamides and renewable Nylon 6,6. As a noncatalytic electrode for the partial hydrogenation to trans-3-hexenedioic acid, CNF@CF achieves a threefold increase in both cumulative productivity and Faradaic efficiency (FE) compared to bare CF. A similar boost in catalytic activity and energy efficiency is observed using Pd/CNF@CF for the hydrogenation of ccMA to adipic acid. These results highlight the opportunities of the CNF@CF platform for electro-organic synthesis and sustainable chemical manufacturing.

electrochemical hydrogenation↗

DOE OSTI2021

Toward Optimizing Electrospun Nanofiber Fuel Cell Catalyst Layers: Microstructure and Pt Accessibility

This work investigates how local ionomer/platinum (Pt) interactions and ionomer distribution in electrospun Pt/Vulcan nanofiber electrodes impact ionomer coverage, proton accessibility, and oxygen reduction reaction (ORR) performance in proton-exchange membrane fuel cells. Insights from various in situ electrochemical diagnostics were utilized in conjunction with ex situ microscopic characterization to understand how the electrode microstructure—both at the aggregate level and near the ionomer/platinum interface—is affected by electrospinning in comparison to ultrasonic spraying. The effect of the carrier polymer poly(acrylic acid) (PAA) concentration from 5–20 wt % (with respect to total ink solids) on the resulting nanofiber morphology is discussed. Electron microscopy observations and CO displacement measurements indicated that Pt/Vulcan nanofibers prepared with a higher PAA concentration (15 wt %) were conformally coated with a film of ionomer on the exterior of the fiber, which resulted in an overall lower ionomer coverage on both Pt and carbon throughout the fiber diameter. In contrast, 10 wt % PAA leads to a uniform intrafiber distribution of the ionomer within the fibers, increasing the overall ionomer coverage and proton accessibility under both wet and dry conditions. These differences in the local ionomer coverage on Pt between 10 and 15 wt % PAA were also attributed to differences in the adsorption/interaction affinities between PAA and the ionomer onto the catalyst surface in the ink using zeta potential measurements. Additional fuel cell electrochemical tests on the electrospun electrodes show improvements in ORR kinetics and high-current-density H 2 /air performance compared to the ultrasonically sprayed electrodes.

25 ENERGY STORAGE↗

DOE OSTI2021

Alignment of Au nanorods along de novo designed protein nanofibers studied with automated image analysis

In this paper, we focus on exploring the directional assembly of anisotropic Au nanorods along de novo designed 1D protein nanofiber templates. Using machine learning and automated image processing, we analyze scanning electron microscopy (SEM) images to study how the attachment density and alignment fidelity are influenced by variables such as the aspect ratio of the Au nanorods, and the salt concentration of the solution. We find that the Au nanorods prefer to align parallel to the protein nanofibers. This preference decreases with increasing salt concentration, but is only weakly sensitive to the nanorod aspect ratio. While the overall specific Au nanorod attachment density to the protein fibers increases with increasing solution ionic strength, this increase is dominated primarily by non-specific binding to the substrate background, and we find that greater specific attachment (nanorods attached to the nanofiber template as compared to the substrates) occurs at the lower studied salt concentrations, with the maximum ratio of specific to non-specific binding occurring when the protein fiber solutions are prepared in 75 mM NaCl concentration.

36 MATERIALS SCIENCE↗

DOE OSTI2023

N-Doped carbon nanoparticles on highly porous carbon nanofiber electrodes for sodium ion batteries

Nitrogen doped carbon nanoparticles on highly porous carbon nanofiber electrodes were successfully synthesized via combining centrifugal spinning, chemical polymerization of pyrrole and a two-step heat treatment. Nanoparticle-on-nanofiber morphology with highly porous carbon nanotube like channels were observed from SEM and TEM images. Nitrogen doped carbon nanoparticles on highly porous carbon nanofiber (N-PCNF) electrodes exhibited excellent cycling and C-rate performance with a high reversible capacity of around 280 mA h g -1 in sodium ion batteries. Moreover, at 1000 mA g -1 , a high reversible capacity of 172 mA h g -1 was observed after 300 cycles. The superior electrochemical properties were attributed to a highly porous structure with enlarged d-spacings, enriched defects and active sites due to nitrogen doping. The electrochemical results prove that N-PCNF electrodes are promising electrode materials for high performance sodium ion batteries.

25 ENERGY STORAGE↗