Onion-like Particles Research Articles

Dielectric Response of Onion-Like Carbon-Based Polymethyl Methacrylate Composites

The dielectric properties of polymethyl methacrylate films with embedded onion-like carbon particles have been studied from 20 Hz to 1 MHz to investigate the structural relaxations of the composite material by varying the temperature between 240 and 520 K. The temperature behaviour of the complex permittivity at a given frequency is found to be strongly dependent on the nanocarbon concentration. A small effect of the onion-like carbon concentration on the beta transition of the polymer composite has been observed, which indicates that the included onion-like carbon particles do not block the rotational degrees of freedom of the ester groups along the polymer chains. By contrast, it has been found that embedding the nanocarbon fillers to the polymethyl methacrylate matrix changes significantly the alpha transition and the melting temperatures in a non-monoto-nous way.

Hierarchically Structured Colloids of Diblock Copolymers and Au Nanoparticles

Onionlike block copolymer particles containing a well-ordered gold nanoparticle array were prepared with the help of amphiphilic block copolymer used as a surfactant. The location of gold nanoparticles ordered in the specific position of block copolymer domain was systematically investigated by tuning the invariant polymerization index of the block copolymer and the areal chain density (Σ) of gold nanoparticles.

Preparation of onion-like multilayered particles comprising mainly poly(iso-butyl methacrylate)-block-polystyrene by two-step AGET ATRP

Synthesis of multilayered composite polymer particles comprising mainly poly(iso-butyl methacrylate)-block-polystyrene (PiBMA-b-PS) has been carried out by the use of two-step activator generated by electron transfer for atom transfer radical polymerization (AGET ATRP) in aqueous microsuspension. PiBMA–Br macroinitiator seed particles were prepared in the first step, followed by swelling with styrene and second step (seeded) polymerization. The blocking efficiency in the second step was found to be crucial with regards to the resulting particle morphology. A disordered sea–island morphology was obtained when the blocking efficiency was 47% (73% conversion), whereas a blocking efficiency of 61% (71% conversion) resulted in the formation of multilayered particles. High blocking efficiency can be achieved by careful adjustment of the activation rate by proper choice of polymerization temperature and amount of reducing agent (ascorbic acid).

Spectral Properties of Gas‐phase Condensed Fullerene‐like Carbon Nanoparticles from Far‐ultraviolet to Infrared Wavelengths

Carbon solids are ubiquitous material in the interstellar space. However, the formation pathway of carbonaceous matter in astrophysical environments as well as in terrestrial gas-phase condensation reactions is not yet understood. Laser ablation of graphite in different quenching gas atmospheres such as pure He, He/H$_2$, and He/H$_2$O at varying pressures is used to synthesize very small, fullerene-like carbon nanoparticles. The particles are characterized by very small diameters between 1 and 4 nm and a disturbed onion-like structure. The soot particles extracted from the condensation zone obviously represent a very early stage of particle condensation. The spectral properties have been measured from the far-ultraviolet (FUV) ($\lambda$=120 nm) to the mid-infrared (MIR) ($\lambda$=15 ~$\mu$m). The seed-like soot particles show strong absorption bands in the 3.4 ~$\mu$m range. The profile and the intensity pattern of the 3.4 ~$\mu$m band of the diffuse interstellar medium can be well reproduced by the measured 3.4 ~$\mu$m profile of the condensed particles, however, all the carbon which is left to form solids is needed to fit the intensity of the interstellar bands. In contrast to the assumption that onion-like soot particles could be the carrier of the interstellar ultraviolet (UV) bump, our very small onion-like carbon nanoparticles do not show distinct UV bands due to ($\pi-\pi$*) transitions.

In Situ Heating TEM Study of Onion-like WS2and MoS2Nanostructures Obtained via MOCVD

We report on the in situ heating transmission electron microscopy (TEM) study of WS2 and MoS2 nanoparticles obtained from metal–organic chemical vapor deposition (MOCVD). The general behavior of MoS2 and WS2 is similar: Round, amorphous particles in the pristine sample transform to hollow, onion-like particles upon annealing. A second type of particle with straight layers exhibits only minor changes. A significant difference between both compounds could be demonstrated in their crystallization behavior. The results of the in situ heating experiments are compared to those obtained from an ex situ annealing process under Ar.

Structural transformations in carbon nanoparticles

The structure of icosahedral carbon (diamond and onion-like) nanoparticles is discussed. It is shown that, in carbon nanoparticles, the reversible structural transformations of icosahedral particles into particles with a shell structure can occur without breaking of bonds or disturbance of their topological integrity. New structural models are proposed and analyzed for carbon nanoparticles. The diffusionless mechanism of reversible transformations between diamond-like and onion-like particles is proposed for the first time.

Nanosized carbon forms in the processes of pressure–temperature-induced transformations of hydrocarbons

The products of thermal conversions of naphthalene, anthracene, pentacene, perylene, and coronene at 8 GPa in the temperature range up to 1300 °C have been studied by scanning electron and high-resolution transmission electron microscopies. As a result, it has been established that various nanometer-sized carbon species (spherical and coalesced two-core onion-like carbon particles, faceted polyhedral particles, graphitic ribbons, graphitic folds, and nanocrystalline diamonds) are present in the conversion products together with micron-sized crystallites of graphite and diamond.

Quantitative Chemical Mapping of Nanostructured “Onionlike” Poly(methyl methacrylate)/Polystyrene Composite Particles by Soft X-ray Microscopy

In earlier work, we have produced micrometer-sized, monodisperse, poly(methyl methacrylate)/polystyrene (PMMA/PS) composite particles having a multilayered structure. A challenge to developing applications for these multilayered particles is the quantitative, spatially resolved chemical analysis of their onionlike layered structure, where some layers are thinner than 100 nm. Scanning transmission X-ray microscopy (STXM) has a spatial resolution of better than 50 nm and sufficient chemical contrast to both observe and quantitate the composition of individual layers without staining. The results of quantitative chemical analysis of the particles and standard P(S-co-MMA) random copolymers by STXM are shown to be in good agreement with 1H NMR measurements of their average composition. Results from chemical quantification of the individual layers of the onionlike particles by STXM are reported. Analyses of samples prepared with and without embedding in epoxy are compared. Our analysis takes into account the finite spatial resolution of the STXM. The extent of intermixing between layers was estimated by comparing the measured results to those generated from an assumed instrumental response function and trial compositional structures. This analysis suggests that the individual layers are relatively pure, although small amounts of intermixing (<15%) are also consistent with the results. Possible origins of intermixed layers are indicated and ways to achieve more pure layers are suggested.

Microstructure and oxidation behaviour of Euro IV diesel engine soot: a comparative study with synthetic model soot substances

In this study, the microstructure and oxidation behaviour of soot from the raw exhaust of a Euro IV test heavy duty (HD) diesel engine are investigated and compared to that of spark-discharge soot and hexabenzocoronene (HBC, C42H18). We find a microstructure-controlled reactivity towards oxidation of all three samples in 5% O2 in N2. The spark-discharge soot with its fine primary particles and fullerenoid structure has an onset temperature of 423K for combustion, while the HBC with its well-ordered crystallites has a high onset temperature of 773K. Due to an improved combustion process in the Euro IV HD diesel engine, the emitted soot consists of more fullerenoid- or onion-like particles agglomerated in a chain-like secondary structure. The onset temperature of the Euro IV HD engine soot combustion is 573K. Oxidation of the three samples produces only CO2 and H2O. The different H2O production profiles can be assigned to the functionalised surface of the samples and depend on the soot structure and preparation route.

Structural transformations in quartz and apatite on mechanical activation

Methods of transmission electron spectroscopy (TEM), micro diffraction, powder X-ray diffraction (XRD), and IR spectroscopy were applied to the investigation of structural transformations of quartz and apatite subjected to mechanical treatment of varying intensity. Threshold mechanical stress equal to the theoretical shear strength was determined. This value separates the region of mechanical grinding and the region where structural and chemical transformations take place. “Liquid-crystal,” “onion-like,” and amorphous particles sized from 1 nm to 100 nm were revealed by TEM in mechanically activated quartz and apatite samples. According to electron diffraction and XRD, in “liquid crystal” quartz nanoparticles the lattice parameter of the starting matrix is preserved in one crystallographic direction, while IR spectra of the material are typical of amorphous silicic acid. Similarity of structural transformations upon indentation of single crystals of apatite and quartz, and during mechanical activation of the minerals in a planetary mill was revealed.

RECENT DISCOVERIES IN CARBON BLACK FORMATION AND MORPHOLOGY AND THEIR IMPLICATIONS ON THE STRUCTURE OF INTERSTELLAR CARBON DUST

In this review we discuss about the presence of carbon under the form of dust grains and organic molecules in the interstellar and circumstellar medium. The spectral evidences about the presence of these carbon-based dust and molecules in the space is also reviewed. We would like to emphasise that the molecules present in space, namely polyyne chains and rings, polycyclic aromatic hydrocarbons and fullerenes which are the precursors of the formation of interstellar carbon dust have been also detected by in situ mass spectrometry in ordinary flames and in the carbon arc formed between graphite electrodes under special conditions. Thus the mechanism which lead to soot formation in a flame should be similar to that leading to carbon dust in space. In fact, the morphology of the carbon black produced industrially by furnace process or by thermal decomposition appears very close to the morphology of carbon dust produced under conditions which should simulate the circumstellar conditions. In both cases curved graphene sheets can be observed together with onion-like particles and defective structures which we have defined fullerene-like structures. The presence of these structures may affect the surface chemistry of the carbon dust grains by enhancing the electron affinity in comparison to graphite.

Transformation of diamond nanoparticles into carbon onions under electron irradiation

The irradiation-induced transformation of diamond nanoparticles (DNP) to spherical onions and onion-like carbon was studied in situ by high-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS). The process was observed in a transmission electron microscope operated at 200 kV without additional specimen heating. Estimated current density was in the range 20–40 A cm−2. The onion-like particles formed from the diamonds were found to be quite stable to further electron irradiation. The changes in chemical bonding were also confirmed by EELS, revealing an increasing role of bonds with sp2 hybridization in the irradiated material. The mechanism of structural transformation is discussed.

Synthesis of carbon 'onions' in water

The fabrication of carbon nanomaterials usually calls for expensive vacuum systems to generate plasmas and yields are disappointingly low. Here we describe a simple method for producing high-quality spherical carbon nano-'onions' in large quantities without the use of vacuum equipment. The nanoparticles, which have C60 cores surrounded by onion-like nested particles, are generated by an arc discharge between two graphite electrodes submerged in water. This technique is economical and environmentally benign, and produces uncontaminated nanoparticles which may be useful in many applications.

Diamond and pore structure observed in wood charcoal

Various carbon structures were observed in the wood charcoal sample: the well known pyrolytic graphite layers, onion-like particles, and diamond structure. It is suggested that wood charcoal carbonized at 700°C is a complex of various carbon structures. The pore structure was observed by electron microscopy, and it is supposed that the microstructure and pores are closely related. Further study of the microstructure during the carbonization process of charcoal is necessary to better understand the characteristic functions of wood charcoal for utilizing it as a source of carbon material.

Synthesis of multi-walled carbon nanotubes by microwave plasma-enhanced chemical vapor deposition

Microwave plasma-enhanced chemical vapor deposition (MW-PECVD) has been employed to synthesize carbon nanostructures by using Fe (or Co, Ni)/γ-Al 2O 3 as catalysts and a mixture of benzene, hydrogen, and argon as precursors. By regulating the types of catalyst, the microwave incident power, the ratio and flux of the precursors, many morphologies such as ordinary geometric, helix-shaped, and planar spiral carbon nanotubes with aspect ratios of 100–1000 have been observed. Furthermore, two novel nanostructures, which are probably the missing link between onion-like carbon particles and nanotubes, have also been obtained. The striking feature of this new approach is the low synthesis temperature (<520°C) due to the non-equilibrium characteristic of microwave plasma operated at low pressure, which is crucial for some fascinating applications.

Thin Films of Carbon Nanocapsules and Onion-Like Graphitic Particles Prepared by the Cosputtering Method

A method for fabricating thin films of carbon nanocapsules and onion-like graphitic particles was reported. The method consists of cosputtering Ni and graphite, and subsequent thermal annealing in vacuum. Transmission electron microscopic and Raman studies revealed that the films were composed of Ni-filled carbon nanocapsules with graphitic coatings several nanometers in thickness. Ni particles were removed by acid etching, resulting in the formation of thin films composed of onion-like graphitic particles. Electron field emission properties of the onion-like graphitic-particle films were studied.

Onion-like graphitic particles observed in wood charcoal

Onion-like graphitic particles were first observed by Iijima in ark-discharge-deposited carbon blacks. 1 When the microstructure of the carbon blacks produced by vacuum evaporation of graphite was studied, onion-like structures were found by high-resolution electron microscopy. These structures were also found by Ugarte after irradiating carbon soot with high-energy (300kV) electron beams for a prolonged period. 2 Other techniques have also been reported to produce similar structures from other substances. 3 Although onion-like graphitic particles are now a well-defined allotropic nanophase of carbon, 4 they have not been found in wood charcoal thus far. This report describes their growth during evolution in wood charcoal. The microstructure of carbonized microfibrils, which were observed in regions close to the groups of onion-like graphitic particles, are also presented in this paper. Materials and methods

The Role of Fullerene-Like Structures in Carbon Black and Their Interaction with Dienic Rubber

The identification of fullerene-like sites on carbon black surface and in particular the pentagonal or corannulene-type sites, has permitted us to explain the chemical interaction between filler and polymer (diene rubber) occurring during mixing in terms of free radical and Diels-Alder addition of polymer chains on the fullerene-like sites of carbon black. The free radicals and diene sites are formed on rubber chains during mixing by the mechanochemical degradation, which is caused by shear stresses. We have also noticed the curious analogy between the turbostratic morphology of carbon black particles and the onion-like graphitic particles.

Evidence for the solubility of boron in graphite by electron energy loss spectroscopy

We present the results of transmission electron microscopy (TEM) and electron energy loss spectrometry (EELS) studies on two carbon–boron alloys both prepared by chemical vapour deposition at ca. 1000°C and differing in their [Boron]/[Carbon] atomic ratio as well as in their morphology. In both samples, impurity concentrations, principally oxygen and nitrogen, were found to be low relative to boron dopant levels. For low boron contents, typically around 5–10 at.%, the sample consisted of onion-like spherical particles approximately 10 nm in diameter which exhibited a non-homogeneous distribution of boron, concentrated at a level of 5–6 at.% in the centre. For this sample, studies of the B–K- and C–K-ELNES (electron energy loss near-edge structure) together with associated modelling of the unoccupied density of electronic states, indicate a substitution of boron atoms on threefold coordinated sp2-sites within the graphite network. For higher boron doping levels, typically 25 at.%, the sample consisted of homogeneous thin films. In this case, the change in shape of the B–K-ELNES indicates that boron has higher coordinations than planar trigonal together with possibly some residual sp2 sites. This study unambiguously demonstrates the presence of boron substitution solely within an sp2-bonded graphite network in the case of low boron contents and, when combined with other studies, gives an indication of the solubility limit for boron in graphite for the chemical vapour deposition (CVD) process.

Growth and Morphology Change of Polystyrene-block-poly(2-cinnamoylethyl methacrylate) Particles in Solvent−Nonsolvent Mixtures before Precipitation

Tetrahydrofuran (THF) and acetonitrile (AN) are good and poor solvents for poly(2-cinnamoylethyl methacrylate) (PCEMA) and polystyrene (PS). Their mixtures with AN volume fractions between 80% and 93% are precipitants for PS but slightly solubilize the PCEMA block of a polystyrene-block-poly(2-cinnamoylethyl methacrylate), PS-b-PCEMA, sample with 380 styrene and 210 CEMA units. Immediately after the addition of AN to a THF solution of the diblock, spherical particles with PCEMA shell and PS core are formed due to phase separation. The core−shell particles then grow in size, presumably mainly due to particle coalescence, and transform into the more complex egglike, onionlike, and berrylike particles in THF/AN with 80%−90% AN before precipitation in several weeks. In THF/AN with 93% AN, no structural mutation is seen in 1 week after the formation of the spherical particles despite eventual polymer precipitation. This resistance of the spherical core−shell particles to morphological transitions may be due to...