Complex Particle Structures Research Articles

Geometrically driven aggregation of unsymmetrical dielectric particles.

Understanding electrostatic interactions among dielectric bodies in the atmosphere and aerosols is central to controlling their aggregation. Polarization effects, which are frequently ignored, are crucial to determine interactions when geometrical anisotropies are present due to surface-induced charge segregation. Here, we adopt a direct integral formulation that accounts for the problem of charged dielectric bodies immersed in a continuum media to explore particle aggregation via geometrical tuning. We show that by breaking the structural symmetry and modifying the close-contact surface between particles of equal charge, it is possible to obtain attractive regimes at short and long distances. We evaluate the electrostatic forces and energy of a set of dimers and trimers composed of spheres, oblates, and prolates in a vacuum, where no counter-ions are present, to construct a phase diagram with the conditions required to form stable aggregates as a function of the geometrical anisotropy. We found that it is possible to direct the aggregation (or dispersion) of two and three positive dielectric particles by adjusting their geometry and controlling the contact surface among them. Our results give insight into a way to control the aggregation of dielectric systems and offer a prospect for directing the assembly of complex particle structures.

Characterization of Fractal Structures by Spray Flame Synthesis Using X-ray Scattering.

In this work, we take on an in-depth characterization of the complex particle structures made by spray flame synthesis. Because of the resulting hierarchical aggregates, very few measurement techniques are available to analyze their primary particle and fractal properties. Therefore, we use small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) to investigate the influence of the precursor concentration on the fractal structures of zirconia nanoparticles. The combination of information gained from these measurement results leads to a detailed description of the particle system, including the polydispersity and size distribution of the primary particles. Based on our findings, unstable process conditions could be identified at low precursor concentrations resulting in the broadest size distribution of primary particles with rough surfaces. Higher precursor concentrations lead to reproducible primary particle sizes almost independent of the initial precursor concentration. Regarding the fractal properties, the typical shape of aggregates for aerosols is present for the investigated range of precursor concentrations. In conclusion, the consistent results for SAXS and TEM show a conclusive characterization of a complex particle system, allowing for the identification of the underlying particle formation mechanism.

Exploring molecular structure characteristics and chemical index of Qinghua bituminous coal: A comprehensive insight from single molecule of macerals to particles with various sizes

Understanding the relationship between the coal structure and its reactive behaviour is of great significance to achieve clean coal conversion and its efficient utilisation. One of the key tasks is to elucidate the molecular structure and chemical bonding information of coal. Owing to the complexity of the chemical structure of coal, studies on the molecular structure of coal, especially coal models with complex particle structures of different sizes for bituminous coal from northwest China, are highly warranted. In this work, the molecular structure characteristics and chemical index of a Qinghua bituminous coal sample collected from the Ningdong area, China, were assessed. Using a combination of material characterization, computation, and molecular modelling methods, a standard method for modelling complex coal structures from single molecules of macerals to particles of various sizes was developed. The single molecular structure of vitrinite and inertinite present in Qinghua coal can be expressed as C269H196N4O13S and C255H179N3O14S, respectively. Then, a series of complex particle models of various sizes were established based on the single molecular structure models of vitrinite and inertinite. Among these models, the size of the complex particles was as large as 11 nm, with the total atomic number approaching 60,000. Furthermore, the energetic and structural features of the complex coal particle structures were also explored based on their energy decomposition and radial distribution function analysis. In addition, the chemical structure index analysis was performed for different coal macerals to further understand the internal relationship between its structure and application.

Seeded-Growth of Silica Rods from Silica-Coated Particles.

Seeded growth of silica rods from colloidal particles has emerged as a facile method to develop novel complex particle structures with hybrid compositions and asymmetrical shapes. However, this seeded-growth technique has been so far limited to colloidal particles of only a few materials. Here, we first develop a general synthesis for the seeded-growth of silica rods from silica particles. We then demonstrate the growth of silica rods from silica-coated particles with three different cores which highlight the generality of this synthesis: fluorescently labeled organo-silica (fluorescein), metallic (Ag), and organic (PS latex). We also demonstrate the assembly of these particles into supraparticles. This general synthesis method can be extended to the growth of silica rods from any colloidal particle which can be coated with silica.

Sulfur Dose and Sulfidation Time Affect Reactivity and Selectivity of Post-Sulfidized Nanoscale Zerovalent Iron.

Exposing nanoscale zerovalent iron (NZVI) to dissolved sulfide species improves its performance as a remediation agent. However, the impacts of sulfur dose and sulfidation time on morphology, sulfur content, reactivity, and selectivity of the resulting sulfidized NZVI (SNZVI) have not been systematically evaluated. We synthesized SNZVI using different sulfur doses and sulfidation times and measured their properties. The measured S/Fe molar ratio in the particles ([S/Fe]particle) was 10-500 times lower than [S/Fe]dosed but was predictable based on [S/Fe]dosed × tsulfidation. The low sulfur content (0.02-0.65 mol % S/Fe) inhibited the reaction of SNZVI with water (up to 13-fold) and increased its reactivity with trichloroethene (TCE) (up to 14-fold) and its electron efficiency (up to 20-fold). A higher [S/Fe]particle (0.86-1.13 mol % S/Fe) led to complex particle structures and lowered the resistance to electron transfer but did not improve the benefits realized at the lower S/Fe ratios. Adding small amounts of sulfur into NZVI led to more accumulation of acetylene, especially for low Fe/TCE conditions, suggesting that sulfur lowers the rate of hydrogenation of acetylene to ethene. These results show that [S/Fe]dosed × tsulfidation can be used to predict the measured S content in the particles and thataffects reactivity, longevity, and electron selectivity, for post-SNZVI.

Modelling the Optical Properties of Metal Nanoparticles: Analytical vs Finite Elements Simulation

Metal nanoparticles are an important research field for their broad and various application. The modeling of their chemical and physical properties is essential for the correct design of innovative materials. In this study the analytical simulation, based on the bare Mie theory, is directly compared with the measured absorbance spectra of gold colloids, prepared through a seed-mediated process. The goodness in the prediction of the particles dimension gives an indication on the level of precision of the model to simulate the optical behavior of the sample. Then, a discrete simulation is performed, which implements finite element analysis; a good level of agreement with the analytical model is obtained for single isolated nanoparticles, and additional properties like electromagnetic behavior of the particles is modeled. At last the discrete simulation is used to explore complex particle structures, whose analytical simulation is not possible, like dimer, nanoparticles chain and planar distribution. For these configurations, the electric field is analyzed, with particular attention to the best configuration for the field enhancement, and the trend of the absorption spectrum is studied as a function of the relative distance among the particles. The results indicate that the plasmon resonance shifts to the red when array of particles are considered since 10 and 30nm shift has been observed for a chain of closely spaced nanoparticles and for a planar ordered nanoparticles, respectively.

Numerical investigation of the grid spatial resolution and the anisotropic character of EMMS in CFB multiphase flow

During the last years, considerable efforts have been made for the optimization of numerical methods simulating the operation of the Circulating Fluidized Bed Combustors (CFBC), which imply both the accuracy increase and the computational cost decrease. A foremost goal is the efficient description of its operation under isothermal conditions and the in-depth understanding of the governing complex multiphase flow mechanisms. Grid construction and the calculation of the drag force experienced by the inert material in the two-phase flow are two important parameters for the optimization of the numerical approaches in the case of CFB simulation. The aim of the present investigation is to investigate both the effect of grid density distribution on simulation results and the validity of an anisotropic approach for the drag force calculation through an Energy Minimization Multi-Scale (EMMS) scheme. Grid density distribution is found to affect the numerical accuracy and the real time of simulations. Uniform grid density distribution is found to be the most efficient choice in terms of balance between computational cost and numerical accuracy. On the other hand, EMMS scheme improves the efficiency of detecting complex particle structures (clusters) without an explicit modeling of these spatio-temporal formations. Moreover, applying EMMS scheme only for calculation of the z-component of drag force yielded better numerical results compared to a constant interphase momentum exchange coefficient for all the three directions.

Synthesis of chitosan‐poly(Acrylic Acid) complex particles by dispersion polymerization and their applications in ph buffering and drug release

AbstractThis research prepared polyelectrolyte complex particles of chitosan‐poly(acrylic acid) (CS‐PAA) through polymerization of acrylic acid (AA) in the presence of chitosan (CS). The prepared CS‐PAA complex particles had positive zeta potential and dispersed very well in the aqueous solution. Structure and morphology of complex particles were investigated with the changes in the feeding molar ratio of glucosamine unit in CS to AA monomer. It was found at a molar ratio of 1.0/1.1, a hollow structure in complex particles was observed after polymerization. From solid state 13C‐NMR and FTIR analyses, the results confirmed that CS‐co‐PAA copolymer was also produced during polymerization in addition to the PAA homopolymer, and both constituted in the structure of complex particles. The synthesized complex particles were environmentally sensitive in which their mean diameter could change with the pH value of medium. Moreover, the complex particles showed a continuous release of the encapsulated doxycycline hyclate up to 8 days. These complex particles with environmentally sensitive properties are expected to be utilized in the hydrophilic drug delivery system. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Salt Effects on Complexes of Oppositely Charged Macromolecules Having Different Affinity to Water

The influence of salt concentration on the size and on the thermodynamic stability of interpolymer complexes composed of oppositely charged macroions having different affinity to solvent was studied from a theoretical viewpoint. It was shown that increasing salt concentration causes changes in the structure of complex particles. At low salt concentration, the particles preserve their structure and size. At a critical salt concentration, nScr, the particle size rises sharply to a slightly larger dimension. From this concentration, the macroions forming the interpolymer complex start to separate, and the complex is fully destroyed at a salt concentration nS*. After separation, the macroions coexist in solution and with further increase in salt concentration reduce their sizes according to the screening of polyion charges by salt ions. nScr and nS* depend on physical parameters such as the degree of polymerization of macroions, their degree of ionization, and macroion−solvent interaction parameters. Experime...

Soft polymer and nano-clay supracolloidal particles in adhesives: synergistic effects on mechanical properties

Numerous synthesis routes toward nanostructured polymer particles have emerged, but few examples demonstrate the essential need for such complex particle structures to achieve any added benefit in a target application. Here, polymer particles having Laponite clay armor were prepared by the Pickering miniemulsion polymerization of n-lauryl acrylate. The resulting “soft–hard” poly(lauryl acrylate) (PLA)–Laponite hybrid particles were blended at various low concentrations with a standard poly(butyl acrylate-co-acrylic acid) (PBA) latex for application as a waterborne pressure-sensitive adhesive (PSA). The tack adhesion properties of the resulting nanocomposite films were compared with the performance of the PBA when blended with either a conventional non-armored PLA latex, with Laponite RD nanosized clay discs, or a mixture of both. A true synergistic effect was discovered showing that the clay-armored supracolloidal structure of the hybrid particles was essential to achieve a superior balance of viscoelastic properties. The addition of small amounts, e.g. 2.7 wt%, of the “soft–hard” clay-armored PLA particles increased the tack adhesion energy considerably more than found for the two individual components or for the sum of their individual contributions. The soft PLA core ensures that the adhesives are not stiffened too much by the nanosized Laponite clay. Slippage at the interface between the nanoclay platelets and the PBA matrix introduces an additional energy dissipation mechanism during deformation. Through the synergistic effect of the clay and PLA in the supracolloidal armored latex structure, the tack adhesion energy is increased by 45 J m−2, which is about 70% greater than found for the PBA adhesive alone.

Catalytic etching of Pt/Rh gauzes

The catalytic etching of 90% (weight) platinum/10% rhodium gauzes in hydrogen/oxygen mixtures was studied. The gauzes were found to etch over exactly the same range of temperatures and gas stoichiometries as pure platinum. In contrast, pure rhodium etched in neither pure gases nor under reaction conditions. In a laminar flow type reactor weight loss of the Pt/Rh gauzes was found to be significant indicating rapid etching and the surfaces smooth and undifferentiated from the untreated material. In contrast, in an impinging jet reactor there was little weight loss, but the surfaces were found to be partially covered by complex particle structures, 1 to 10 μm across. Analysis of the particles showed them to have virtually the same composition as the original gauze. The application of a new model of catalytic etching of single metals to this system explained some, but not all, of the observations. The model explains the limited range of conditions under which etching was observed, as well as the formation of particles in the impinging jet reactor; however, the model failed to explain completely the presence of rhodium in the particles.