In situ observation of synthesized nanoparticles in ultra-dilute aerosols via X-ray scattering

In-air epitaxy of nanostructures (Aerotaxy) has recently emerged as a viable route for fast, large-scale production. In this study, we use small-angle X-ray scattering to perform direct in-flight characterizations of the first step of this process, i.e., the engineered formation of Au and Pt aerosol nanoparticles by spark generation in a flow of N₂ gas. This represents a particular challenge for characterization because the particle density can be extremely low in controlled production. The particles produced are examined during production at operational pressures close to atmospheric conditions and exhibit a lognormal size distribution ranging from 5–100 nm. The Au and Pt particle production and detection are compared. We observe and characterize the nanoparticles at different stages of synthesis and extract the corresponding dominant physical properties, including the average particle diameter and sphericity, as influenced by particle sintering and the presence of aggregates. We observe highly sorted and sintered spherical Au nanoparticles at ultra-dilute concentrations (< 5 × 10⁵ particles/cm³) corresponding to a volume fraction below 3 × 10^–10, which is orders of magnitude below that of previously measured aerosols. We independently confirm an average particle radius of 25 nm via Guinier and Kratky plot analysis. Our study indicates that with high-intensity synchrotron beams and careful consideration of background removal, size and shape information can be obtained for extremely low particle concentrations with industrially relevant narrow size distributions.

     

Poly(styrene-g-ethylene oxide) copolymers as interfacial agents in immiscible polymer blends

A poly(styrene-g-ethylene oxide) copolymer with an average of 100 styrene units between the graft points is studied with respect to its interfacial activity in binary incompatible mixtures of polymers having different degrees of miscibility toward the graft copolymer components. The interfacial properties were studied by scanning electron microscopy, dynamic mechanical spectroscopy, and differential scanning calorimetry. The data obtained are compared with previously published data from a graft copolymer with the same composition but with shorter PEO branches and only 20 styrene units between them. In spite of their structure, the two graft copolymers could reduce the size of the dispersed phase in the case of athermal mixing. With a negative heat of mixing between only one graft component and the blend, the short branch graft had no effect, while the longer branch graft caused a reduction of the size of the dispersed phase. With a negative heat of mixing for the graft branches as well as for the backbone a strong compatibilizing effect was found for both types of graft copolymers. The results show that even very short parts of the backbone of a graft copolymer can contribute to compatibilization in a polymer blend, especially when the backbone has a negative heat of mixing with one of the blend components.     

Cross-linking and N-(1-pyrenyl)maleimide labeling of cysteine mutants of proton-pumping pyridine nucleotide transhydrogenase of Escherichia coli

The pyridine nucleotide transhydrogenase of Escherichiacoli is a proton pump composed of two subunits (alpha and beta) organized as an alpha2beta2 tetramer. The enzyme contains seven cysteine residues, five in the alpha-subunit and two in the beta-subunit. The reaction of these residues with the cross-linking agent cupric 1, 10-phenanthrolinate and with the fluorescent thiol reagent N-(1-pyrenyl)maleimide was investigated in mutants in which one or more of these cysteine residues had been mutated to serine or threonine residues. Mutation of alphaCys395 and alphaCys397 prevented disulfide bond formation to give the cross-linked alpha2 dimer. We concluded that the two alpha-subunits of the holoenzyme interface in the region of these two cysteine residues. Pyrenylmaleimide reacted with detergent-washed cytoplasmic membrane vesicles containing high levels of transhydrogenase protein to show characteristic fluorescence emission bands at 378-379, 397-398, and 419-420 nm. At higher ratios of pyrenylmaleimide:transhydrogenase (>5:1) and longer times of reaction, an eximer band at 470 nm was formed. This was attributed to interaction between noncovalently bound molecules of pyrenylmaleimide. The cysteine residues of the beta-subunit (betaCys147 and betaCys260) were covalently modified by pyrenylmaleimide. betaCys147 reacted more strongly than betaCys260 with the fluorophore, and the pyrene derivative of betaCys147 was more accessible to quenching by 5-doxylstearate, suggesting a proximity to the surface of the membrane. Covalent modification of betaCys260 resulted in inhibition of enzyme activity. The inhibition was attributed to the introduction of the bulky pyrene group into the enzyme.     

A Versatile and Convenient Synthesis of 34S‐Labeled Phosphorothioate Oligonucleotides

A synthetic protocol for ³⁴S‐labeled phosphorothioate oligonucleotides (PS ONs) was developed to facilitate MS‐based assay analysis. This was enabled by a highly efficient, two‐step, one‐pot synthesis of ³⁴S‐labeled phenylacetyl disulfide (³⁴S‐PADS), starting from ³⁴S‐enriched elemental sulfur (³⁴S₈). ³⁴S‐PADS was subsequently used for stable isotope labeling (SIL) of oligonucleotides containing a phosphorothioate backbone. The ³⁴S‐SIL PS ONs are shown to retain the same melting temperature, antisense activity, and secondary structure as those of the corresponding unlabeled ³²S PS ONs.     

Hydrogen-assisted spark discharge generated metal nanoparticles to prevent oxide formation

There exists a demand for production of metal nanoparticles for today's emerging nanotechnology. Aerosol-generated metal nanoparticles can oxidize during particle formation due to impurities in the carrier gas. One method to produce unoxidized metal nanoparticles is to first generate metal oxides and then reduce them during sintering. Here, we propose to instead prevent oxidation by introducing the reducing agent already at particle formation. We show that by mixing 5% hydrogen into the nitrogen carrier gas, we can generate single crystalline metal nanoparticles by spark discharge from gold, cobalt, bismuth, and tin electrodes. The non-noble nanoparticles exhibit signs of surface oxidation likely formed post-deposition when exposed to air. Nanoparticles generated without hydrogen are found to be primarily polycrystalline and oxidized. To demonstrate the advantages of supplying the reducing agent at generation, we compare to nanoparticles that are generated in nitrogen and sintered in a hydrogen mixture. For bismuth and tin, the crystal quality of the particles after sintering is considerably higher when hydrogen is introduced at particle generation compared to at sintering, whereas for cobalt it is equally effective to only add hydrogen at sintering. We propose that hydrogen present at particle generation prevents the formation of oxide primary particles, thus improving the ability to sinter the nanoparticles to compact and single crystals of metal. This method is general and can be applied to other aerosol generation systems, to improve the generation of size-controlled nanoparticles of non-noble metals with a suitable reducing agent.

Copyright © 2018 American Association for Aerosol Research     

Review of Spark Discharge Generators for Production of Nanoparticle Aerosols

In the growing field of nanotechnology there is an increasing need to develop production methods for nanoparticles, especially methods that provide control and reproducibility. The spark discharge generator (SDG) is a versatile device for the production of nanoparticle aerosols. It can produce aerosol nanoparticles in the entire nanometer range (1–100 nm), and beyond. Depending on requirements, and the system used, these nanoparticles can be completely contamination free and composed of one or more materials. This provides a unique opportunity to create new materials on the nanoscale. Already in use in semiconductor, materials, health and environmental research, the SDG shows promise for yet more applications. If needed, particle production by the SDG could be scaled up using parallel generators facilitating continuous high-volume production of aerosol nanoparticles. Still, there is a surprisingly low knowledge of fundamental processes in the SDG. In this article we present a thorough review of the most common and relevant SDGs and the theory of their operation. Some possible improvements are also discussed.

Copyright 2012 American Association for Aerosol Research     

Erratum to: In situ observation of synthesized nanoparticles in ultra-dilute aerosols via X-ray scattering

Nano Research - The article In situ observation of synthesized nanoparticles in ultradilute aerosols via X-ray scattering, written by Sarah R. McKibbin, Sofie Yngman, Olivier Balmes, Bengt O....