Publications

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Despite their many advantages, covalent organic frameworks (COFs) built from three-dimensional monomers are synthetically difficult to functionalize. Herein, we provide a new synthetic approach to the functionalization of a three-dimensional covalent organic framework (COF-300) by using a series of solid-state linkage transformations. By reducing the imine linkages of the framework to amine linkages, we produced a more hydrolytically stable material and liberated a nucleophilic amino group, poised for further functionalization. We then treated the amine-linked COF with diverse electrophiles to generate a library of functionalized materials, which we tested for their ability to adsorb perfluoroalkyl substances (PFAS) from water. The framework functionalized with dimethylammonium groups, COF-300-dimethyl, adsorbed more than 250 mg of perfluorooctanoic acid (PFOA) per 1 g of COF, which represents an approximately 14,500-fold improvement over that of COF-300 and underscores the importance of electrostatic interactions to PFAS adsorption performance. In conclusion, this work provides a conceptually new approach to the design and synthesis of functional three-dimensional COFs.

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The properties of materials can change dramatically at the nanoscale new and useful properties can emerge. An example is found in the paramagnetism in iron oxide magnetic nanoparticles. Using magnetically sensitive nitrogen-vacancy centers in diamond, we developed a platform to study electron spin resonance of nanoscale materials. To implement the platform, diamond substrates were prepared with nitrogen vacancy centers near the surface. Nanoparticles were placed on the surface using a drop casting technique. Using optical and microwave pulsing techniques, we demonstrated T1 relaxometry and double electron-electron resonance techniques for measuring the local electron spin resonance. The diamond NV platform developed in this project provides a combination of good magnetic field sensitivity and high spatial resolution and will be used for future investigations of nanomaterials and quantum materials.

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Self-assembly of iron oxide nanoparticles (IONPs) into 1D chains is appealing, because of their biocompatibility and higher mobility compared to 2D/3D assemblies while traversing the circulatory passages and blood vessels for in vivo biomedical applications. In this work, parameters such as size, concentration, composition, and magnetic field, responsible for chain formation of IONPs in a dispersion as opposed to spatially confining substrates, are examined. In particular, the monodisperse 27 nm IONPs synthesized by an extended LaMer mechanism are shown to form chains at 4 mT, which are lengthened with applied field reaching 270 nm at 2.2 T. The chain lengths are completely reversible in field. Using a combination of scattering methods and reverse Monte Carlo simulations the formation of chains is directly visualized. The visualization of real-space IONPs assemblies formed in dispersions presents a novel tool for biomedical researchers. This allows for rapid exploration of the behavior of IONPs in solution in a broad parameter space and unambiguous extraction of ​the parameters of the equilibrium structures. Additionally, it can be extended to study novel assemblies formed by more complex geometries of IONPs.

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Sandia National Laboratories sponsored a three-year internally funded Laboratory Directed Research and Development (LDRD) effort to investigate the vulnerabilities and mitigations of a high-altitude electromagnetic pulse (HEMP) on the electric power grid. The research was focused on understanding the vulnerabilities and potential mitigations for components and systems at the high voltage transmission level. Results from the research included a broad array of subtopics, covered in twenty-three reports and papers, and which are highlighted in this executive summary report. These subtopics include high altitude electromagnetic pulse (HEMP) characterization, HEMP coupling analysis, system-wide effects, and mitigating technologies.

Controlling the formation of nanosized branched nanoparticles with high uniformity is one of the major challenges in synthesizing nanocatalysts with improved activity and stability. Using a cubic-core hexagonal-branch mechanism to form highly monodisperse branched nanoparticles, we vary the length of the nickel branches. Lengthening the nickel branches, with their high coverage of active facets, is shown to improve activity for electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF), as an example for biomass conversion.

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The magnetic susceptibility of NOx-loaded RE-DOBDC (rare earth (RE): Y, Eu, Tb, Yb; DOBDC: 2,5-dihydroxyterephthalic acid) metal-organic frameworks (MOFs) is unique to the MOF metal center. RE-DOBDC samples were synthesized, activated, and subsequently exposed to humid NOx. Each NOx-loaded MOF was characterized by powder X-ray diffraction, and the magnetic characteristics were probed by using a VersaLab vibrating sample magnetometer (VSM). Lanthanide-containing RE-DOBDC (Eu, Tb, Yb) are paramagnetic with a reduction in paramagnetism upon adsorption of NOx. Y-DOBDC has a diamagnetic moment with a slight reduction upon adsorption of NOx. The magnetic susceptibility of the MOF is determined by the magnetism imparted by the framework metal center. The electronic population of orbitals contributes to determining the extent of magnetism and change with NOx (electron acceptor) adsorption. Eu-DOBDC results in the largest mass magnetization change upon adsorption of NOx due to more available unpaired f electrons. Experimental changes in magnetic moment were supported by density functional theory (DFT) simulations of NOx adsorbed in lanthanide Eu-DOBDC and transition metal Y-DOBDC MOFs.

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Soft matter has historically been an unlikely candidate for investigation by electron microscopy techniques due to damage by the electron beam as well as inherent instability under a high vacuum environment. Characterization of soft matter has often relied on ensemble-scattering techniques. The recent development of cryogenic transmission electron microscopy (cryo-TEM) provides the soft matter community with an exciting opportunity to probe the structure of soft materials in real space. Cryo-TEM reduces beam damage and allows for characterization in a native, frozen-hydrated state, providing direct visual representation of soft structure. This article reviews cryo-TEM in soft materials characterization and illustrates how it has provided unique insights not possible by traditional ensemble techniques. Soft matter systems that have benefited from the use of cryo-TEM include biological-based “soft” nanoparticles (e.g., viruses and conjugates), synthetic polymers, supramolecular materials as well as the organic–inorganic interface of colloidal nanoparticles. We conclude that while many challenges remain, such as combining structural and chemical analyses; the opportunity for soft matter research to leverage newly developed cryo-TEM techniques continues to excite.

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The ability to print three-dimensional objects was first developed in the 1980s and was originally strictly limited to polymeric materials. Through most of the intervening years, the approach has been thought of as a rapid prototyping method. This allowed low volume, high fidelity structures to be quickly fabricated to test things like fit and finish. However, more recently the term additive manufacturing has entered usage to represent the same methods and implies that the field is transitioning to creating finished parts. When we begin to think about these techniques as a real manufacturing approach, then the materials properties achieved during manufacture become much more important. This is true for all materials, as additive manufacturing has grown to encompass structures formed from metals and ceramics, however the bulk of work remains centered on polymers.

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Soft magnetic materials are key to the efficient operation of the next generation of power electronics and electrical machines (motors and generators). Many new materials have been introduced since Michael Faraday's discovery of magnetic induction, when iron was the only option. However, as wide bandgap semiconductor devices become more common in both power electronics and motor controllers, there is an urgent need to further improve soft magnetic materials.These improvements will be necessary to realize the full potential in efficiency, size, weight, and power of high-frequency power electronics and high-rotational speed electrical machines. Here we provide an introduction to the field of soft magnetic materials and their implementation in power electronics and electrical machines. Additionally, we review the most promising choices available today and describe emerging approaches to create even better soft magnetic materials.

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Significant reductions recently seen in the size of wide-bandgap power electronics have not been accompanied by a relative decrease in the size of the corresponding magnetic components. To achieve this, a new generation of materials with high magnetic saturation and permeability are needed. Here, we develop gram-scale syntheses of superparamagnetic Fe/FexOy core-shell nanoparticles and incorporate them as the magnetic component in a strongly magnetic nanocomposite. Nanocomposites are typically formed by the organization of nanoparticles within a polymeric matrix. However, this approach can lead to high organic fractions and phase separation; reducing the performance of the resulting material. Here, we form aminated nanoparticles that are then cross-linked using epoxy chemistry. The result is a magnetic nanoparticle component that is covalently linked and well separated. By using this 'matrix-free' approach, we can substantially increase the magnetic nanoparticle fraction, while still maintaining good separation, leading to a superparamagnetic nanocomposite with strong magnetic properties.

This article focuses on the finite element modeling of toroidal microinductors, employing first-of-its-kind nanocomposite magnetic core material and superparamagnetic iron nanoparticles covalently cross-linked in an epoxy network. Energy loss mechanisms in existing inductor core materials are covered as well as discussions on how this novel core material eliminates them providing a path toward realizing these low form factor devices. Designs for both a 2 μH output and a 500 nH input microinductor are created via the model for a high-performance buck converter. Both modeled inductors have 50 wire turns, less than 1 cm3 form factors, less than 1 Ω AC resistance, and quality factors, Q's, of 27 at 1 MHz. In addition, the output microinductor is calculated to have an average output power of 7 W and a power density of 3.9 kW/in3 by modeling with the 1st generation iron nanocomposite core material.

A method for creating nanoparticles directly from bulk metal by applying ultrasound to the surface in the presence of a two-part surfactant system is presented. Implosive collapse of cavitation bubbles near the bulk metal surface generates powerful microjets, leading to material ejection. This liberated material is captured and stabilized by a surfactant bilayer in the form of nanoparticles. The method is characterized in detail using gold, but is also demonstrated on other metals and alloys, and is generally applicable. It is shown that nanoparticles can be produced regardless of the bulk metal form factor, and the method is extended to an environmentally important problem, the reclamation of gold from an electronic waste stream.

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A magnetically active Fe3O4/poly(ethylene oxide)-block-poly(butadiene) (PEO-b-PBD) nanocomposite is formed by the encapsulation of magnetite nanoparticles with a short-chain amphiphilic block copolymer. This material is then incorporated into the self-assembly of higher order polymer architectures, along with an organic pigment, to yield biosynthetic, bifunctional optical and magnetically active Fe3O4/bacteriochlorophyll c/PEO-b-PBD polymeric chlorosomes.

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Core–shell nanostructures are promising candidates for the next generation of catalysts due to synergistic effects which can arise from having two active species in close contact, leading to increased activity. Likewise, catalysts displaying added functionality, such as a magnetic response, can have increased scientific and industrial potential. Here, Pd/Fe3O4 core–shell nanowire clusters are synthesized and applied as hydrogenation catalysts for an industrially important hydrogenation reaction: the conversion of acetophenone to 1-phenylethanol. During synthesis, the palladium nanowires self-assemble into clusters which act as a high-surface-area framework for the growth of a magnetic iron oxide shell. This material demonstrates excellent catalytic activity due to the presence of palladium while the strong magnetic properties provided by the iron oxide shell enable facile catalyst recovery.

Extensive study of photorefractive polymeric composites photosensitized with semiconductor nanocrystals has yielded data indicating that the inclusion of such nanocrystals enhances the charge-carrier mobility, and subsequently leads to a reduction in the photorefractive response time. Unfortunately, the included nanocrystals may also act as a source of deep traps, resulting in diminished diffraction efficiencies as well as reduced two beam coupling gain coefficients. Nonetheless, previous studies indicate that this problem is mitigated through the inclusion of semiconductor nanocrystals possessing a relatively narrow band-gap. Here, we fully exploit this property by doping PbS nanocrystals into a newly formulated photorefractive composite based on molecular triphenyldiamine photosensitized with C60. Through this approach, response times of 399 μs are observed, opening the door for video and other high-speed applications. It is further demonstrated that this improvement in response time occurs with little sacrifice in photorefractive efficiency, with internal diffraction efficiencies of 72% and two-beam-coupling gain coefficients of 500 cm-1 being measured. A thorough analysis of the experimental data is presented, supporting the hypothesized mechanism of enhanced charge mobility without the accompaniment of superfluous traps. It is anticipated that this approach can play a significant role in the eventual commercialization of this class of materials.

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Ternary polymer brushes consisting of polystyrene, poly(methyl methacrylate), and poly(4-vinylpyridine) have been synthesized. These brushes laterally phase separate into several distinct phases and can be tailored by altering the relative polymer composition. Self-consistent field theory has been used to predict the phase diagram and model both the horizontal and vertical phase behavior of the polymer brushes. All phase behaviors observed experimentally correlate well with the theoretical model.

Magnetic nanoparticles are the next tool in medical diagnoses and treatment in many different biomedical applications, including magnetic hyperthermia as alternative treatment for cancer and bacterial infections, as well as the disruption of biofilms. The colloidal stability of the magnetic nanoparticles in a biological environment is crucial for efficient delivery. A surface that can be easily modifiable can also improve the delivery and imaging properties of the magnetic nanoparticle by adding targeting and imaging moieties, providing a platform for additional modification. The strategy presented in this work includes multiple nitroDOPA anchors for robust binding to the surface tied to the same polymer backbone as multiple poly(ethylene oxide) chains for steric stability. This approach provides biocompatibility and enhanced stability in fetal bovine serum (FBS) and phosphate buffer saline (PBS). As a proof of concept, these polymer-particles complexes were then modified with a near infrared dye and utilized in characterizing the integration of magnetic nanoparticles in biofilms. The work presented in this manuscript describes the synthesis and characterization of a nontoxic platform for the labeling of near IR-dyes for bioimaging.

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