Spontaneous coalescence in ultrafine metal particle aggregates

In the preparation of ultrafine metal particles (Cu, Ti, Ni or Al) by opposed-targets dc sputtering, a substrate cooled by liquid helium flow was used, on which the metal clusters and argon atoms were condensed simultaneously, forming a solid layer of the mixture. By raising the temperature of the substrate and the argon pressure in the chamber, the solid argon melts and evaporates, remaining the metal-particle aggregates. After complete evaporation of the argon, a phenomenon was observed in which the metal-particle aggregates shrank and suddenly changed their colour from black to bulk-metal colour, followed by an explosion-like noise. We offer an explanation for this phenomenon by the mechanism of spontaneous coalescence due to the large surface energy of the ultrafine particles. From our observation and analysis, we conclude that a certain particle size exists, below which the spontaneous coalescence may occur in a very fast way, leading to melting of the particles. The fast process of coalescence, melting and cooling introduces large internal stress which splits the sintered particle, giving the explosion-like noise. This phenomenon may imply a size limitation in forming nanocrystalline solid materials of pure metals.     

Multifractal model of gas diffusion in polymers

A probabilistic (multifractal) model of gas diffusion in polymer membranes is proposed. This model has a simple and clear physical meaning and provides fairly accurate predictions of the diffusivities of various gases. For the latter purpose, a minimum set of structural characteristics is required.     

Capillary gas chromatographic analysis of pyrrolidinedithiocarbamate metal chelates

Pyrrolidinedithiocarbamate (PDTC) chelates of Zn(II), Cu(II), Ni(II), Co(III), Fe(III), Mn(II), Cr(III), and VO(II) were analysed by capillary GC on a DB-1701 column (30 m x 0.25 mm id) with flame ionisation detection (FID). Linear calibrations were attained within "1-30 microg/mL" for Ni(II), Fe(III), Mn(II), Cr(III), Cu(II), and VO(II), and within "2-50 microg/mL" for Co(III) and Zn(II). The limits of detection were in the "150-500 ng/mL" range, corresponding to 15-50 pg amounts reaching the FID system. The optimised method was applied to the determination of Cu(II) and Ni(II) in coins, and that of Zn(II), Cu(II), Ni(II), Fe(III), Mn(II), Cr(III), and VO(II) in pharmaceutical preparations with relative standard deviations within 1.1-5.2%. The results obtained are in good agreement with sewage water samples and the declared values for the pharmaceutical formulations, or with the results of AAS of metal contents in coins, pharmaceutical preparations, and sewage water samples.     

The desaggregation of solid particle aggregates by ultrasonication

The influence of some variables (concentration, intensity, and time) of ultrasonication on the mean particle size is determined by ultracentrifugation and capillary viscosimetry. For the fused silica Aerosil 200^® under optimal conditions only an aggregate radius of 23 nm is achieved. That means an irreversible fused aggregate of about 21 primary particles which contains 60% v/v of immobilized water.     

Surfactant self-assembly in the gas phase: bis(2-ethylhexyl)sulfosuccinate-alkaline metal ion aggregates

The coating effect of alkali metal salt clusters by the surfactant anion bis(2-ethylhexyl)sulfosuccinate has been investigated by electrospray ionization mass spectrometry (MS) and MS/MS. The analysis of the data emphasized the formation and stability in the gas phase of reverse micelle-like surfactant aggregates carrying in their interior ionic clusters. Two main contributions have been postulated to account for the observed stability: intra-aggregate electrostatic interactions and screening of inter-aggregate attractive interactions due to the exclusion volume effect caused by the surfactant alkyl chains. Moreover, the stability and structural arrangement of these supramolecular aggregates result in strong dependency on the alkali metal salt identity.     

First mixed hydrazide/hydroxylamide metal aggregates

The first organometallic clusters of mixed hydrazide/hydroxylamide clusters of zinc, [Zn(MeZn)(4)(HNNMe(2))(2)(ONEt(2))(4)] and {Zn(EtZn)(4)[HNN(CH(2))(5)](2)(ONEt(2))(4)} were synthesized in one-pot synthesis protocols from dialkylzinc solutions, substituted hydrazines and N,N-diethylhydroxylamine; competing for the Zn atoms, the different binding properties of hydrazide and hydroxylamide ligands in these heteroleptic clusters are discussed.     

Simulation of ESR spectra of metal nanoparticle aggregates

Aggregates of polydisperse particles characterized by the preset values of the fractal dimensions and prefactor are built with the use of a special algorithm. ESR spectra of such aggregates are calculated in the self-consistent field approximation. It is shown that, even in sufficiently large aggregates with fractal structure, spectra greatly depend on the character of packing of large and small particles in the aggregate.     

Structure of polymer and particle aggregates in hydrogel composites

Knowledge of the structure of a biomaterial is usually vital to control its function. This article provides a structural characterization of a hyaluronan scaffold that has demonstrated good biocompatibility and is used to induce bone regeneration. Hyaluronan hydrogels are appealing materials that can function as a matrix to incorporate both organic and inorganic substances to enhance tissue growth. Because of the intrinsic properties of this swollen matrix, one needs a very sensitive technique that can be applied in situ to determine the organization of the polymers in a gel. Small-angle neutron scattering is used to determine the characteristics of the inhomogeneous structure of the hydrogel both with and without added particles. The results are interpreted using models of structure with two length scales that are beyond the traditional picture of homogeneous gels. The observed structure and the dimensions can explain the previously reported rheological properties of gels containing different amount of polymers. Hydroxyapatite nanoparticles added to the gel are frozen in the gel matrix. We are able to determine the distribution and shape of these particles as they aggregate around the polymer chains. We have also concluded, in this case, that the particle structure is concentration independent. Information about the nanostructure for an applicable biomaterial guides the formulation, preparation, and use that should lead to further understanding of its exploitation. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Viscosity of nanofluids: particle shape and fractal aggregates

Colloidal dispersions of nanoparticles in thermal base fluids are known to alter their spherical shapes thereby affecting their surface properties. This aspect has been investigated with respect to the effective viscosity of nanofluids presuming the particles to acquire the shape of prolate spheroid. Also, the contributions of the interfacial layer formed around these particles and their possible agglomeration has been taken in to account. The analysis has been carried out by modifying the Krieger and Dougherty model. The relative viscosity of these nanofluids has been computed as a function of volume fraction, particle size and the eccentricity of the particle. The model also incorporates the concept of fractal dimensions. The results thus obtained compare significantly well with the available experimental data and reaffirms an improvement over earlier models.     

Multifractal analysis of nanodeformation of glassy polymer surface

The multifractal approach has been employed to quantitatively analyze an intact glassy polymer (polystyrene) surface and that deformed in an atomic force microscope. An algorithm has been described in detail for constructing generalized fractal dimension spectra. These spectra have been shown to provide information that reasonably reflects the properties of the studied reliefs of a polystyrene surface.     

Multifractal analysis of sputtered CaF2 thin films

The surface morphologies of CaF₂ thin films prepared by electron beam evaporation technique were measured by atomic force microscopy. The films were bombarded by energetic ion beams of different fluences, which modified the surface morphology predominantly via the process of erosion. The dependence of the surface morphology on ion fluence was explored using multifractal analysis. It was found that the roughness of the film first decreased with ion fluence but increased at higher fluences. Copyright © 2013 John Wiley & Sons, Ltd.     

Multifractal analysis of dynamic potential surface of ion-conducting materials

A multifractal analysis using singularity spectra [T.C. Halsey et al., Phys. Rev. A 33, 1141 (1986)] provides a general tool to study the temporal-spatial properties of particles in complex disordered materials such as ions in ionically conducting glasses and melts. Obtained by molecular-dynamics simulations, the accumulated positions of the particles dynamically form a structural pattern called the dynamical potential surface. In this work, the complex dynamical potential surfaces of Li ions in the lithium silicates were visualized and characterized by the multifractal analysis. The fractal dimensions and strength of the singularity related to the spatial intermittency of the dynamics are examined, and the relationship between dynamics and the singularity spectra is discussed.     

Diastereoselective fragmentation of chiral alpha-aminophosphonic acids/metal ion aggregates

Diastereomeric clusters of general formula [MAB(2)](+) and [MA(2)B](+) (M = Li(I), Na(I), Ag(I), Ni(II)-H, or Cu(II)-H; A = (R)-(-)- and (S)-(+)-(1-aminopropyl)phosphonic acid; B = (1R)-(-)- and (1S)-(+)-(1-aminohexyl)phosphonic acid) have been readily generated in the electrospray ionization (ESI) source of a triple-quadrupole mass spectrometer and their collision-induced dissociation (CID) investigated. CID of diastereomeric complexes, e.g. [MA(S)(B(S))(2)](+) and [MA(R)(B(S))(2)](+), leads to fragmentation patterns characterized by R(homo) = [MA(S)B(S)](+)/[M(B(S))(2)](+) and R(hetero) = [MA(R)B(S)](+)/[M(B(S))(2)](+) abundance ratios, which depend upon the relative stability of the diastereomeric [MA(S)B(S)](+) and [MA(R)B(S)](+) complexes in the gas phase. The chiral resolution factor R(chiral) = R(homo)/R(hetero) is found to depend not only on the nature of the M ion but also on that of the fragmenting species, whether [MAB(2)](+) or [MA(2)B](+). The origin of this behavior is discussed.     

Ultrafast electron relaxation dynamics in coupled metal nanoparticles in aggregates

We report the effect of aggregation in gold nanoparticles on their ultrafast electron-phonon relaxation dynamics measured by femtosecond transient absorption pump-probe spectroscopy. UV-visible extinction and transient absorption of the solution-stable aggregates of gold nanoparticles show a broad absorption in the 550-700-nm region in addition to the isolated gold nanoparticle plasmon resonance. This broad red-shifted absorption can be attributed to contributions from gold nanoparticle aggregates with different sizes and/or different fractal structures. The electron-phonon relaxation, reflected as a fast decay component of the transient bleach, is found to depend on the probe wavelength, suggesting that each wavelength interrogates one particular subset of the aggregates. As the probe wavelength is changed from 520 to 635 nm across the broad aggregate absorption, the rate of electron-phonon relaxation increases. The observed trend in the hot electron lifetimes can be explained on the basis of an increased overlap of the electron oscillation frequency with the phonon spectrum and enhanced interfacial electron scattering, with increasing extent of aggregation. The experimental results strongly suggest the presence of intercolloid electronic coupling within the nanoparticle aggregates, besides the well-known dipolar plasmon coupling.     

Multifractal analysis for Cu/Ti bilayer thin films

Two bilayer thin films with different stacking sequences, Cu/Ti/Si and Ti/Cu/Si, were deposited by DC magnetron sputtering technique. X‐ray diffraction technique was used to measure the crystallization structures, and scanning electron microscopy and atomic force microscopy were used to measured surface morphology. The multifractal spectra f(α)‐α was used to characterize the surface morphology. The result of |q|_max ≤ 53 is obtained by multifractal analysis. The shape of the multifractal spectra f(α) ? α is hook‐like for Cu/Ti/Si and bell jar‐like for Ti/Cu/Si. The spectrum width Δα = α_max ? α_min and Δf(=f(α_min) ? f(α_max)) of the multifractal spectra is able to quantitatively analyze the growth and surface roughness of the Cu/Ti bilayer thin films. The surface of Ti/Cu/Si thin film is more uniform and smoother than the film of Cu/Ti/Si. Copyright © 2013 John Wiley & Sons, Ltd.     

Multifunctional aggregates for precise cellular analysis

Science China Chemistry - Precisely analyzing the target materials in living cells can reveal the essence and mystery of life at a deeper level, which will provide reliable theoretical basis for...     

Direct analysis of ultra-trace semiconductor gas by inductively coupled plasma mass spectrometry coupled with gas to particle conversion-gas exchange technique

An inductively coupled plasma mass spectrometry (ICPMS) coupled with gas to particle conversion-gas exchange technique was applied to the direct analysis of ultra-trace semiconductor gas in ambient air. The ultra-trace semiconductor gases such as arsine (AsH₃) and phosphine (PH₃) were converted to particles by reaction with ozone (O₃) and ammonia (NH₃) gases within a gas to particle conversion device (GPD). The converted particles were directly introduced and measured by ICPMS through a gas exchange device (GED), which could penetrate the particles as well as exchange to Ar from either non-reacted gases such as an air or remaining gases of O₃ and NH₃. The particle size distribution of converted particles was measured by scanning mobility particle sizer (SMPS) and the results supported the elucidation of particle agglomeration between the particle converted from semiconductor gas and the particle of ammonium nitrate (NH₄NO₃) which was produced as major particle in GPD. Stable time-resolved signals from AsH₃ and PH₃ in air were obtained by GPD-GED-ICPMS with continuous gas introduction; however, the slightly larger fluctuation, which could be due to the ionization fluctuation of particles in ICP, was observed compared to that of metal carbonyl gas in Ar introduced directly into ICPMS. The linear regression lines were obtained and the limits of detection (LODs) of 1.5 pL L⁻¹ and 2.4 nL L⁻¹ for AsH₃ and PH₃, respectively, were estimated. Since these LODs revealed sufficiently lower values than the measurement concentrations required from semiconductor industry such as 0.5 nL L⁻¹ and 30 nL L⁻¹ for AsH₃ and PH₃, respectively, the GPD-GED-ICPMS could be useful for direct and high sensitive analysis of ultra-trace semiconductor gas in air.     

Electric dipole moments of particle aggregates in magnetite colloidal solutions in liquid dielectrics

The permanent electric moments and the electric polarizability anisotropy of particle aggregates are determined from the results of measuring the birefringence of a magnetite colloidal solution in kerosene subjected to constant and pulsed electric fields. A possible mechanism of generating an induced dipole moment in the aggregates is analyzed. The moment is characterized by a long relaxation time and, according to the results of optical experiments, is interpreted as permanent. The calculated dipole moments are consistent with the experimental data in the order of magnitude.     

Structure flexibility of iridium metal aggregates. Comparison with platinum and rhodium

The atomic structure of iridium aggregates occluded in zeolite has been studied by radial electron distribution from X-ray scattering data taken under different atmospheres. The interatomic distances in 1–2 nm naked aggregates are contracted with respect to the bulk distances. The adsorption of hydrogen produces a relaxation but a residual contraction remains unlike in the case of platinum aggregates. The carbon monoxide adsorption produces little effect on the position of surface iridium atoms unlike on platinum and rhodium. The lack of structure flexibility of iridium aggregates is probably due to the higher cohesive energy of iridium.