Elementary Particle Size Research Articles

Ultrasound assisted crystallization of a new cardioactive prototype using ionic liquid as solvent

This work deals with the antisolvent crystallization of LASSBio-294 (3,4-methylenedioxybenzoyl-2-thienylhydrazon) assisted by ultrasound. An ionic liquid (IL), 1-ethyl-3-methylimidazolium methyl phosphonate [emim][CH3O(H)PO2] was used as solvent and water as antisolvent. The influence of the following parameters on crystals properties (size distribution, morphology, residual solvent and in vitro dissolution) were studied with two mixing mode (quick and dropwise) of solution with antisolvent. The impact of washing and drying process was also evaluated. Comparative studies of conventional crystallization conditions (without ultrasound) were also performed. The effect of ultrasound on LASSBio-294 recrystallized properties was influenced by the add mode, water/IL ratio and drug solution concentration. As example, US promoted the formation of small crystals with high residual IL under the following conditions: quick addition, high drug solution concentration and high water/IL ratio. However, despite the decrease of elementary particle size, ultrasound did not avoid crystals agglomeration. The drug dissolution rate was affected by the physical structure of agglomerates. When employed as drying process of washed crystals, spray drying reduced this agglomeration and improved the dissolution of LASSBio-294 crystals.

Multifunctional gold coated iron oxide core-shell nanoparticles stabilized using thiolated sodium alginate for biomedical applications

In this paper we report synthesis of aqueous based gold coated iron oxide nanoparticles to integrate the localized surface plasma resonance (SPR) properties of gold and magnetic properties of iron oxide in a single system. Iron oxide-gold core shell nanoparticles were stabilized by attachment of thiolated sodium alginate to the surface of nanoparticles. Transmission electron microscope (TEM) micrograph presents an average elementary particle size of 8.1±2.1nm. High resolution TEM (HR-TEM) and X-ray photon spectroscopy further confirms the presence of gold shell around iron oxide core. Gold coating is responsible for reducing saturation magnetization (Ms) value from ~41emu/g to ~24emu/g – in thiolated sodium alginate stabilized gold coated iron oxide core-shell nanoparticles. The drug (curcumin) loading efficiency for the prepared nanocomposites was estimated to be around 7.2wt% (72μgdrug/mg nanoparticles) with encapsulation efficiency of 72.8%. Gold-coated iron oxide core-shell nanoparticles could be of immense importance in the field of targeted drug delivery along with capability to be used as contrast agent for MRI & CT.

Floc Cohesive Force in Reversible Aggregation: A Couette Laminar Flow Investigation

A simple theoretical model is proposed to describe the limiting size of aggregates attained at steady state under given shear conditions. The stable size is assumed to be the result of a dynamic equilibrium between simultaneous aggregate growth and breakup that are represented as first-order processes. The theory establishes that the evolution of steady-state aggregate size versus shear rate is written as the sum of two exponential laws. The validity of the model is verified by direct observation of the coagulation behavior of latex particles in the stagnant plane of a counter-rotating Couette reactor. The influence of latex elementary particle size, initial particle volume fraction, and inner gap spacing of Couette reactor, are investigated. In all cases, the model shows good agreement with the experimental results. Aggregate growth proceeds with a monomodal size distribution that exhibits a scaling behavior. Such monomodal distribution evolves toward broad and even bimodal steady-state distributions at both low and high shear rates, whereas a narrow monomodal pattern is observed at intermediate shear gradients. The aggregate cohesive force F(C) can be calculated from the critical shear rate of dislocation defined by the model. In contrast to the broadly accepted view that larger flocs should be more fragile than smaller aggregates, we find that F(C) scales as D(3/2) where D is the aggregate characteristic diameter. The latter relationship may be derived by assuming linear elasticity of aggregates.

Synthesis of platinum nano-particles in high-temperatures and high-pressures fluids

Colloidal dispersions of platinum nano-particles have been synthesized by the reduction of platinum ion(IV) in the hightemperature and high-pressure water, ethanol, and water–ethanol mixtures in the presence of the protective polymer of poly( Nvinyl-2-pyrrolidone) (PVP). The syntheses have been tested at various temperatures (from 100 to 300 ◦ C) and pressures (from 5 to 25 MPa). The diameter and the composition have been examined by UV-Vis, extended X-ray absorption fine structure (EXAFS), and transmission electron micrograph (TEM), respectively. At 200 ◦ C and 25 MPa, colloidal dispersions of platinum particles of small size (2.6 ± 0.5 nm) were synthesized from 1:1 mixture of water and ethanol within a few seconds. From the analysis of the EXAFS, it is suggested that the elementary particle size obtained under the present condition is larger than that obtained under the ambient condition. We have also succeeded in producing the colloidal dispersions in aqueous solution, although the size and its distribution were relatively larger than the case of water–ethanol mixture. In ethanol solution we could not synthesize a well-dispersed colloidal solution at high temperatures. The possibility of the regulation of the particle size and distribution is discussed. © 2003 Elsevier B.V. All rights reserved.

Hydrothermal synthesis and morphology control of boehmite

The effect of synthesis conditions on the size and morphology of boehmite particles in the sol produced by hydrothermal processing has been investigated. Transmission electron microscopy, X-ray diffraction and Laser particle size analysis were used to characterise the synthesized boehmite. Results show that the initial hydrothermal solution pH has a significant effect on the particle size and morphology. As the pH changes from low (acid) to high (alkaline), the morphology changes from a “needle-like” one to a “platelet” one. Under the conditions investigated here, the synthesis temperature and time in comparison have little apparent effect on the particle size. However, the precursor concentration, while having little noticeable effect on the elementary particle size, does result in extensive agglomeration when it is very high.

Water retention properties of the clay in soils developed on clayey sediments: significance of parent material and soil history

We have investigated the water retention properties of clayey subsoil horizons according to the variation of clay characteristics. The horizons studied developed on a large range of age and facies of calcareous or calcium-saturated clayey sediments. The water retention properties were studied from −10 hPa to −15 000 hPa water potential using small clods collected in winter when swelling is at a maximum and water content close to field capacity. The specific water content and volume of the clods at field conditions, their specific volume at −15 000 hPa water potential, the clay content, the organic carbon content, the cation exchange capacity, the N2-BET surface area and calcareous content were measured. The clay fabric, which is the spatial distribution of the elementary clay particles, was quantified when the soil was close to field capacity and we could attribute the whole pore volume to the porosity of the clay fabric. Our results show that the water retention properties of the clay vary greatly from one soil to another with respect to the clay fabric. The variation of the latter depends on the cation exchange capacity, the size of elementary particles and hydric stress history of the clay. We show that the water retention properties of the studied clayey soils vary according to the clay content and fabric, the latter being related either to parent material fabric or to both the hydric history of the soil and size of the elementary clay particles.

On Viscoelastic, Birefringent, and Swelling Properties of Laponite Clay Suspensions: Revisited Phase Diagram

Relations between thermodynamics, structural, and mechanical properties of Laponite suspensions were recently discussed in the literature. One important issue concerning the liquid/gel transition of the Laponite suspensions is to understand why a mechanical gel appears concomitantly with what appears as an incomplete nematic transition. To get some insight, we first give a more extended characterization of the viscoelastic properties of these suspensions near the liquid/gel transition. For this purpose, stress relaxation experiments are compared to direct determinations of the viscoelastic modulus in the frequency domain. This permits the following of viscoelastic properties, in the linear regime, on a very extended scale, from 10-5 to 102 rad/s. The data show that the relaxation mechanisms are very slow and are compatible with the presence of a large scale structural organization compared to the elementary particle size. The elastic modulus follows the power law: G‘ = A(C − C0)α. Only the concentration threshold varies with the ionic strength. In a second part, we compare, on the same system, how the osmotic pressure and the birefringent properties are correlated. As already shown by Gabriel et al., three optical domains can be defined, an isotropic liquid, an isotropic gel, and a birefringence gel, where numerous threadlike defects highly reminiscent of nematic texture are observed. An interesting new result is seen, a line that separates the isotropic and the birefringent gel coincides with the line where the plateau of the osmotic pressure ends up. Recalling that the osmotic plateau starts just at the liquid/solid transition, we propose a more complete phase diagram exhibiting a pseudobiphasic region with no macroscopic phase separation.

Physicochemical Characterization of Silicalite-1 Nanophase Material

A silicalite-1 nanophase material with an elementary particle size of 18−100 nm is synthesized from clear solution and isolated and purified using supercentrifugation. The nanopowder is characterized in detail using scanning electron microscopy, high-resolution transmission electron microscopy, attenuated force microscopy, 29Si magic angle spinning NMR, 13C cross polarization magic angle spinning NMR, X-ray diffraction, dinitrogen physisorption, and thermogravimetric analysis and compared with micrometer-sized silicalite-1. The nanosized and micrometer-sized materials have many common properties including the refined structure and the nature and concentrations of tetrapropylammonium species incorporated during the synthesis. Unique properties of the nanophase are a splitting of the characteristic framework vibration at 550 cm-1 into a doublet at 555 and 570 cm-1, a high concentration of defect sites, and a strain in the crystallites along the “a” crystallographic direction. The nanophase exhibits a two-st...

Network structure of fine silica particles

The network structure of silica aerogels heated at 300, 400 and 500°C in dried air have been determined by neutron total scattering measurements using a pulsed spallation neutron source. SANS experiments were also performed to obtain the particle size of the silica constituting aerogel. The elementary particle size obtained is about 13A in diameter. The distances of the Si-O and O-O interactions in such fine silica particles are 1.61 and 2.64 A, respectively, which are the same as those of fused silica. The coordination numbers of these pairs are found to be less evident than those of fused silica. In addition, the distances of the Si-Si pairs in the aerogels are slightly longer than that of fused silica. According to the heat treatment temperature, the coordination numbers of the Si-O and O-O interactions increase and the distance of the Si-Si pair decreases. These results indicate that although the network structure of fine silica particles treated at lower temperature is loose and imperfect, such structure can be changed by heating at relatively low temperature. The Raman spectra and the skeletal density measurements of the aerogels support also these results.

Absorption and Scattering Coefficients of Titanium Dioxide Particulate Suspensions in Water

Precise kinetic studies of photocatalytic reactions in solid catalyst water suspensions require the accurate description of the radiation fieldlight distributioninside the reactor. Solution of the radiative transport equation (RTE) inside the reaction is one of the best ways of accessing to such information. For solving this equation, a minimum of two parameters (the absorption and scattering coefficients) and one scattering spatial distribution function (the phase function) are needed. These attributes are directly associated with the optical behavior of the reacting system and are not independent of catalysts more conventional properties. A complete report on the physical and optical characteristics of titanium dioxide particulate suspensions in water is presented. Results were obtained for six different commercially available powders. The investigated parameters were (i) size of elementary particles, (ii) size of particle aggregates in water suspensions, (iii) specific surface area, (iv) spectral extin...

Syntheses of submicron magnesium oxide powders

Submicron MgO powders have been synthesized from thermal decomposition of magnesium chelates or acetate at around 200 °C in liquid alcohol or supercritical alcohol-CO 2 mixtures. Because of a similar coordination of the magnesium atom in both types of precursors, a common amorphous alkoxy-hydroxy derivative is first obtained. When the reaction occurs in a supercritical medium with carbon dioxide as cosolvent, the microstructure of the solid is quite different and a CO 2 group is incorporated into the alkoxy bond. In all cases, the intermediate compound crystallizes into cubic magnesium oxide under thermal treatment between 400 and 600 °C; the elementary particle size in the powders obtained is less than 100 nm.

Characterization of TSSS paint coatings for solar collectors by FTIR spectroscopy

The background to the spectral selectivity of thickness sensitive spectrally selective (TSSS) paint coatings is discussed from the chemical point of view. This means considering the solar absorptance ( a s) and thermal emittance ( e T) of the TSSS paint coatings as a function of paint film thicknesses in terms of the degree of flocculation of the pigment dispersion and from the viewpoint of the relevant intermolecular interactions which influence the ability of the pigment particles to become distributed uniformly in the paint, thus increasing its colour strength. We investigated eight TSSS paint coatings based on the standard formulation of Solariselect ® paint [Sol. Energy Mater. 18 (1989) 97], which is currently used for solar collector panels. The influence of carbon soot (C - Degussa FW2), inorganic pigment (F - Ferro 6331) and fumed silica thixotropic agent (Aerosil - Degussa) in TSSS paint coatings on the degree of their flocculation was determined from the infrared hemispherical reflectivity R ( d) λ = 2.5 which was measured from the paint film thickness. The absorption coefficient for diffuse radiation ( K) and the scattering coefficient ( S) were determined by fitting the experimentally determined R ( d) λ = 2.5 curves to a modified Kubelka-Munk function derived by Körte and Otto [Appl. Spectrosc. 43 (1988) 38]. Correlations between the type of black pigment (F and C) and elementary particle size and surface activity of fumed silica (Aerosil 380, 200 and 972) were established and compared with the experimentally determined solar absorptance values ( a s) of the corresponding TSSS paint coatings. Since fumed silica in spite of its small content (<1% by weight) in the paint dispersion, decreases the gloss of the paint, the correlation between the RMS heights of irregularities (σ) and RMS slopes ( m) of irregularities derived from the infrared reflectivity measurements according to the procedure by Bennett and Porteus [J. Opt. Soc. Am. 51 (1961) 123] were determined. This revealed that the σ values are inversely proportional to the elementary particle size of the fumed silica used (Aerosil 380, 200, 972) in the TSSS paint coatings. FTIR spectra of Solariselect ® paints, the corresponding TSSS paint coatings and model dispersions prepared from the resin binder (phenoxy resin) and various types of Aerosils were measured, and the influence of the composition of the paint dispersions on the frequency shifts of -OH vibrations and intensity changes of skeletal modes of the resin binder were established. The changes of infrared bands observed revealed that resin binder molecules become more strongly bonded when fumed silica is present in dispersions. The correlation among the strength of the interactions in a dispersion, the degree of flocculation and σ values are given and discussed.

Influence of surface area and particle size of dispersed oxide on conductivities of lithium bromide composite electrolytes

Temperature dependent conductivities are reported for composites of LiBr and of LiBr·H 2O with a range of both non-porous and porous dispersed oxides. Enhanced conductivity is observed for both systems with high surface area aluminas. Porous aluminas with similar surface area to enhancing non-porous aluminas give large enhancements despite their much larger elementary particle size. Conductivity enhancements in LiBr·H 2O composites below the temperature characteristic of the α/sB phase transition of LiBr·H 2O prevent the conductivity loss characteristic of that phase at lower temperatures. No simple trend in conductivity enhancement with oxide mole fraction is transferable between oxides. A non-porous silica of similar surface area to enhancing aluminas does not give the same enhancements.

Elementary particle size distribution and PVC plastisol viscosity

Abstract This article deals with our research on the relationship between the amount of fixed plasticizer and the plastisol viscosity of PVC having a sharp bimodal particle size distribution. The following conclusions are derived. Plastisol viscosity is related to the porosity based on a glass beads model experiment in which the particle size distribution is similar to that of the actual plastisol. High shear rate viscosity is more dependent on a change of fixed plasticizer content than low shear rate viscosity.

Effects of Aggregation of Reactant Powder Particles on the Kinetics and Mechanism of Solid State Reaction between BaCO3 and TiO2

Mechanism and kinetics of the solid state reaction have. been studied with special emphasis on the effects of aggregation of reactant powder particles. Equimolar mixtures of BaCO3 and TiO2 were prepared by partial precipitation and ball milling methods using two kinds of TiO2 powders with approximately the same ele-mentary particle size in different states of aggregation.It is shown that BaTiO3 is the only product when fine TiO2 was used but that aggregated TiO2 yielded additional products Ba2TiO4 and BaTi4O9. Disintegration of large TiO2 aggregates by ball-milling decreased the amounts of additional products, and prolonged ball-milling led to substantially the same reaction products and kinetics as those observed with fine TiO2. No single rate equation has been successfully applied to reaction isotherms obtained with different mixtures. Kinetic behavior has been interpreted in terms of the relative amounts of the reaction products as influenced by the state of aggregation of reactant powder particles.

Newton's gravitational constant

The formula for Newton's gravitational constant [Formula: see text] follows from a previous conjecture by the author regarding quantized gravitational theory and the size of elementary particles. It is observed that this formula does not conflict with geophysical and astrophysical evidence. Moreover, this formula for Newton's gravitational constant has the desirable feature of exhibiting no dependence on the speed of light.