Colloidal crystals made of poly(N-isopropylacrylamide) microgel particles

Poly (N-isopropylacrylamide) microgel particles are found to form colloidal crystals similar to those occurring in typical hard-sphere colloids like poly(methylmethacrylate) beads. Samples made of particles with different cross-linker concentrations are investigated and their deswelling ratio is determined using dynamic light scattering. Small-angle neutron scattering data are also presented and analysed in terms of a face-centred-cubic crystal structure. The characteristic length, a, of the elementary cell is found to be 535 ± 16 and 495 ± 15 nm for the two systems investigated. This leads to particle radii of 189 ± 6 and 175 ± 5 nm, respectively. These values compare well to the radii determined using several different methods. Received: 26 July 1999/Accepted: 21 March 2000     

Myocardial infarction patients show altered lipoprotein properties and functions when compared with stable angina pectoris patients

Several parameters and risk factors were compared between Korean male myocardial infarction (MI) patients (n = 10) and angina pectoris (AP) patients (n = 17) to search unique biomarkers for myocardial infarction (MI) in lipoprotein level. Individual serum and lipoprotein fractions (VLDL, LDL, HDL₂, HDL₃) were isolated and analyzed by lipid and protein determination and enzyme assay. The MI group was found to have a 25 and 30% higher serum cholesterol and triacylglycerol (TG) level than the AP group, respectively, however, their body mass index (BMI), LDL-cholesterol (C), HDL-C, and glucose levels fell within the normal range. MI patients were found to have an approximately two-fold higher level of serum IL-6 and an 18% lower serum apoA-I level than that of the AP group. LDL and HDL₂ fraction of the MI group were more enriched with TG than those of AP group. The increased TG was correlated well with the increased level of apoC-III in the same fraction. Cholesteryl ester transfer protein (CETP) activity and protein level were greatly increased in MI patients in the LDL and HDL₃ fractions. MI patients showed more severely oxidized LDL fraction than patients in the AP group, as well as the weakest antioxidant ability of serum. Conclusively, MI patients were found to have unique serum and lipoprotein characteristics including increased IL-6 and TG in serum, with CETP and apoC-III in the LDL and HDL fractions, as well as severely impaired antioxidant ability of HDL.     

Electrochemical reduction and kinetics of hydrogen peroxide on the rotating disk palladium-plated aluminum electrode modified by Prussian blue film as an improved electrocatalyst

This paper describes the use of an aluminum electrode plated by metallic palladium and modified by Prussian blue (PB/Pd-Al) in the electrocatalytic reduction of hydrogen peroxide (H₂O₂). The effect of pH on the electroreduction of H₂O₂ on the modified electrode is investigated and a simple irreversible reduction pathway is suggested. The electroreduction kinetics including transfer coefficient α, potential-dependent charge transfer rate constants k _f, and diffusion coefficient D are estimated by means of forced hydrodynamic voltammetry using a rotating disk PB/Pd-Al electrode. The mean values obtained for kinetics are 0.38, 10⁻² cm⁻¹, and 7.6 × 10⁻⁶ cm² s⁻¹, respectively. The long-term stability of the modifying layers on the Al substrate was studied.     

Short-time self-diffusion coefficient of a particle in a colloidal suspension bounded by a microchannel: virial expansions and simulation

Self-diffusion of colloidal particles confined to a cylindrical microchannel is considered theoretically and numerically. Virial expansion of the self-diffusion coefficient is performed. Two-body and three-body hydrodynamic interactions are evaluated with high precision using the multipole method. The multipole expansion algorithm is also used to perform numerical simulations of the self-diffusion coefficient, valid for all possible particle packing fractions. Comparison with earlier results shows that the widely used method of reflections is insufficient for calculations of hydrodynamic interactions even for small packing fractions and small particles radii, contrary to the prevalent opinion.     

Measurement of the hydrodynamic radii of PEE-G dendrons by diffusion spectroscopy on a benchtop NMR spectrometer

Benchtop nuclear magnetic resonance (NMR) spectroscopy is a useful tool for the rapid determination of the self-diffusion coefficient and the hydrodynamic radius of dendrons. The self-diffusion coefficients of the first four generations of poly ethoxy ethyl glycinamide (PEE-G) dendrons are measured by diffusion-ordered spectroscopy (DOSY) on a benchtop NMR equipped with diffusion gradient coils. The hydrodynamic radii of the dendrons are calculated via the Stokes–Einstein equation. The effects of solvent and pH are determined with the hydrodynamic radius increasing with generation and decreasing upon neutralization of an acidic solution. These measurements provide valuable information for biological and pharmaceutical applications of dendrons.     

Study of sulfur heterogeneous nucleation from supersaturated vapor on tungsten oxide and sodium chloride seed particles. Determination of contact angle of critical sulfur nuclei

A procedure has been developed for determining the contact angle of a critical nucleus formed on seed particles during the heterogeneous nucleation of a vapor in a flow chamber. The procedure comprises the determination of the fraction of enlarged particles, as well as the selective separation of nanoparticles over sizes to locate the zone of intense nucleation. The concentration and size distribution of aerosol particles have been measured with a diffusion spectrometer of aerosols. Vapor concentration distributions and supersaturation fields have been determined by solving the mass-transfer problem. The calculated supersaturation fields are in good agreement with the location of the intense nucleation zone experimentally found with the help of selective separation. The fractions of enlarged particles have been determined as functions of supersaturation in the chamber. A formula has been derived for calculating the fraction and size distribution function of enlarged particles at known supersaturation and temperature fields and a preset contact angle. The contact angles are selected in a manner such that the calculated fraction of enlarged particles coincides with that measured experimentally. It has been revealed that the contact angle of critical sulfur nuclei formed on tungsten oxide seed particles with average radii 〈R _p〉 ≈ 5.8?4.4 nm is in a range of 21.2?20.5°, while, in the case of sodium chloride seed particles with 〈R _p〉 ≈ 6.0?4.4 nm, the contact angle is 20.4?17.4°. The size of a critical nucleus has been found to be proportional to calculated average radius of a seed particle 〈R _p〉 in both cases.     

Detection Limits of Grazing-Exit EPMA for Particle Analysis

 In conventional electron probe microanalysis (EPMA), the electron-induced X-rays are measured at large take-off angles of about 45°. In the grazing exit EPMA (GE-EPMA) method, they are measured at small angles (< 1°). X-rays emitted from deep positions can not be detected at grazing exit angles due to refraction effects at sample-vacuum interface; therefore, it is possible to measure X-rays emitted only from near the surface with a low background. GE-EPMA is especially suitable for the analysis of particles deposited on a flat sample carrier. The detection limits of GE-EPMA were investigated for artificial particles (Al₂O₃, Fe₂O₃ and PbO₂ , particle sizes: 1 ∼ 18 μm) deposited on flat sample carriers of Au thin films–Si wafers. The detection limits improved with decreasing exit angle. The detection limits for characteristic X-rays at an exit angle of approximately 1.1° were 2–4 times lower than at 45°. A minimum detection limit of ca. 0.1% was obtained for Al in small particles.     

Microemulstion synthesis of powders of water-soluble energy-saturated salts

The feasibility of preparing energy-saturated salts (NH₄NO₃, KNO₃, and NaBH₄) in powders with various particle sizes in microemulsion systems based on oxyethylated surfactant Tergitol NP-4 has been demonstrated. Powders were isolated by destroying microemulsions with acetone. The regions of micellar synthesis have been determined depending on the solubilization capacities and concentrations of the reagents and salts at a fixed Tergitol NP-4 concentration (0.25 mol/L). The morphologies and particle sizes of the thus-prepared salt powders were characterized by scanning electron microscopy (SEM), X-ray powder diffraction, differential scanning calorimetry (DSC), differential thermal analysis (DTA), and thermogravimetry; the hydrodynamic radii of microemulsions were characterized by photon-correlation spectroscopy.     

Application of the van der Pauw Methodto Conductivity Relaxation Experimentson YBa2Cu3O6+δ

Summary.  The van der Pauw method has been applied to conductivity relaxation experiments on YBa₂Cu₃O_6+δ at 600°C in order to determine the chemical diffusion coefficient as a function of the oxygen partial pressure in the surrounding atmosphere (10⁰ > p _{O 2}/bar > 10⁻³). It is shown that the van der Pauw technique is suitable for monitoring the conductivity relaxation when the oxygen diffusion is perpendicular to the direct current flowing through the sample in accordance with the van der Pauw geometry using thin tablets as samples. The oxygen partial pressure is changed stepwise (generally Δlogp _{O 2} ≤ 0.5) by employing appropriate gas mixtures as well as an electrochemical oxygen pump device. An evaluation formula is given for the determination of the chemical diffusion coefficient neglecting slow surface processes. In addition, the electronic conductivity of YBa₂Cu₃O_6+δ has been measured at 600°C as a function of oxygen partial pressure of the ambient atmosphere (10⁰ > p _{O 2}/bar > 10⁻⁵) by means of the van der Pauw method applying the same experimental set-up. Typical values of the chemical diffusion coefficient are in the range of 10⁻⁶ cm²·s⁻¹; the results of the conductivity measurements are interpreted in terms of an appropriate defect model. Received May 30, 2000. Accepted June 8, 2000     

Kinetics Characterization of Ion Release under Dynamic and Batch Conditions. I. Weak Acid and Weak Base Ion Exchange Resins

The aim of the present work is concerned with a study of the kinetics of release of both Ca²⁺ and F⁻ from the corresponding loaded ion-exchange resins (weak acid and weak base character for Ca²⁺ for F⁻, respectively), using both dynamic and batch experimental conditions with an artificial saliva solution as the ion-exchange media at 293 and 310 K. The influence of resin particle size and the temperature were evaluated by the kinetics parameters for the effective rate of release (B) and diffusion coefficient (D). The rate of ion release increases with temperature and decreases with particle size. The experimental data were well fitted by models based on intraparticle diffusion-controlled processes. In dynamic studies, the linear dependence of −log ₁₀(B) with the diameter of the resin particles can be applied for the estimation of B values when resins of low particle size are considered. In batch processes, although resins of low particle size can be studied, a linear relationship was only attained for the case of slow ion-exchange kinetic systems.     

Development of new methods for the analysis of carboxylic acids and carbonyl compounds in size classified raindrops by CE for application in modelling atmospheric processes

Summary At the present time the formation processes of clouds and precipitation are not totally understood. Because cloud- and raindroplets are major sinks for chemical species in the atmosphere it is important to understand the physical and the chemical processes which occur during precipitation. The development of models is hindered by the scarcity of information about the scavenging of gases or aerosol particles by raindrops of different sizes. These processes can only be investigated by field experiments using microanalytical methods and analysing single raindrops as well as size-classified raindrop samples. Raindrops were collected according to their size by freezing them in liquid nitrogen (“Guttalgor” method). Sample volumes of the smallest raindrop sizes (radius <200μm) were usually smaller than 2 μL. The analysis of microvolumina in the size range of μL down to pL required the development of methods designed especially for this purpose. Analysis of rain samples was carried out by capillary electrophoresis. Organic acids were determined using a new electrolyte system for indirect detection. With this system it was possible to determine monocarboxylic acids (C₁−C₄) dicarboxylic acids (C₂−C₄, C₉) and inorganic anions (Cl⁻, NO₃ ⁻, SO₄ ²⁻) in the rain samples. Carbonyl compounds were analysed after derivatisation with dansylhydrazine using direct UV-detection. The system allows the identification of aliphatic carbonyl compounds (C₁−C₃, C₅) as well as benzaldehyde. It was found that carbonyl compounds and carboxylic acids showed concentration maxima at different raindrop radii. These concentration maxima are a consequence of particle scavenging. By using the results of a former experiment we concluded that the two species are located on different aerosol particle sizes. Reasons for the different particle sizes where these species are located are discussed. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

Monodisperse micron-sized crosslinked polystyrene particles. IV. Effect of network structure on polymerization procedure

Monodisperse micron-sized polystyrene particles crosslinked using urethane acrylate were produced by dispersion polymerization in ethanol solution and the effect of the crosslinked network structure on the polymerization procedure was studied. The influences of the concentrations of the initiator and urethane acrylate on the particle diameter (D _n), the particle number density (N _p), and the polymerization rate (R _p) were found to obey the approximate relationships D _n ∝ [initiator]^0.43 [urethane acrylate]^0.05, N _p ∝ [initiator]^−1.30 [urethane acrylate]^0.19, and R _p ∝ [initiator]^{0.24 ± 0.02}. The power-law dependence of D _n and N _p on the initiator concentration showed a similar trend to that of linear polystyrene reported in the literature. Especially, it was found that urethane acrylate does not have a serious effect on D _n and N _p of the particles produced. The dependence of R _p on the initiator concentration was observed to be higher than that of linear polystyrene, suggesting that there is still competition between heterogeneous polymerization and solution polymerization because of the crosslinked network structure of the primary particle. Received: 1 April 1999 Accepted in revised form: 29 June 1999     

Slow salt-induced aggregation of citrate-covered silver particles in aqueous solutions of cellulose derivatives

In this work, the salt-induced aggregation of bare and polymer-covered silver particles has been studied with the aid of light scattering and UV-visible spectroscopy. Light scattering on a suspension of bare silver particles at a low salt concentration shows that the cluster fractal dimension d _f changes from 1.6 to 2 in the course of the aggregation process, whereas no restructuring of the clusters is observed at a higher salinity where d _f ≈ 1.6. The growth of the clusters over time can be described by a power law R _h ∝ t ^α , where R _h is the apparent hydrodynamic radius. The UV-visible experiments revealed that increasing the size of the bare silver particles lead to a significant broadening and red-shift of the absorbance band, whereas for salt-induced growth of Ag clusters, a blue-shift and broadening was observed. Addition of salt to a suspension of silver particles and hydroxyethylcellulose divulged a slower broadening of the surface plasmon peak than without polymer.     

Particle size characterization by quadruple-detector hydrodynamic chromatography

Particle size and shape and their distribution directly influence a variety of end-use material properties related to packing, mixing, and transport of powders, solutions, and suspensions. Many of the techniques currently employed for particle size characterization have found limited applicability for broadly polydisperse and/or nonspherical particles. Here, we introduce a quadruple-detector hydrodynamic chromatography (HDC) method utilizing static multiangle light scattering (MALS), quasi-elastic light scattering (QELS), differential viscometry (VISC), and differential refractometry (DRI), and apply the technique to characterizing a series of solid and hollow polystyrene latexes with diameters in the approximate range of 40–400 nm. Using HDC/MALS/QELS/VISC/DRI, we were able to determine a multiplicity of size parameters and their polydispersity and to monitor the size of the particles across the elution profile of each sample. Using self-similarity scaling relationships between the molar mass and the various particle radii, we were also able to ascertain the shape of the latexes and the shape constancy as a function of particle size. The particle shape for each latex was confirmed by the dimensionless ratio ρ ≡ R _G,z /R _H,z which, in addition, provided information on the structure (compactness) of the latexes as a function of particle size. Solid and hollow polystyrene latex samples were also differentiable using these methods. Extension of this method to nonspherical, fractal objects should be possible.       

Electrophoresis of colloidal α-alumina

Measurements of the electrophoretic mobility (u _E) of particles of colloidal α-alumina were made as a function of pH, electrolyte concentration and electrolyte type (NaCl, NaNO₃ and KCl) using two similar instrumental techniques. Significant differences (50% or less) in the values of u _E of particles in NaCl were obtained from the two instruments; however, the isoelectric points (IEPs) (the pH at which u _E=0), estimated from the two sets of measurements, occurred at 7.5 ± 0.3 and 7.8 ± 0.05 and were not significantly different. The latter estimate corresponds with those for particles in KCl and NaNO₃ of 8.05 ± 0.11 and 7.95 ± 0.18, respectively, made using the same instrument and indicate that the IEP was a weak function of electrolyte type. When cations acted as counterions (pH > IEP), the absolute magnitudes and the ranges of u _E with electrolyte concentration were found to be significantly less than when anions acted as counterions (IEP > pH). Estimates of the zeta potential (ζ), made using various procedures, showed variations of up to 25% at low ratios of electrical-double-layer thickness (κ ⁻¹) to particle radius (a) (κa∼10) and were of a similar scale to differences in u _E, but no significant variations (95% confidence) in ζ were obtained at high values (κa∼200). Received: 12 July 2000 Accepted: 17 October 2000     

Metal‐Directed Self‐Assembly of a Polyoxometalate‐Based Molecular Triangle: Using Powerful Analytical Tools to Probe the Chemical Structure of Complex Supramolecular Assemblies

A polyoxometalate‐based molecular triangle has been synthesized through the metal‐driven self‐assembly of covalent organic/inorganic hybrid oxo‐clusters with remote pyridyl binding sites. The new metallomacrocycle was unambiguously characterized by using a combination of ¹H NMR spectroscopy, 2D diffusion NMR spectroscopy (DOSY), electrospray ionization travelling wave ion mobility mass spectrometry (ESI‐TWIM‐MS), small‐angle X‐ray scattering (SAXS) and molecular modelling. The collision cross‐sections obtained from TWIM‐MS and the hydrodynamic radii derived from DOSY are in good agreement with the geometry‐optimized structures obtained by using theoretical calculations. Furthermore, SAXS was successfully employed and proved to be a powerful technique for characterizing such large supramolecular assemblies.     

Nanomolar determination of hydrazine by TiO2 nanoparticles modified carbon paste electrode

In the present paper, the use of a novel carbon paste electrode modified by N,N′(2,3-dihydroxybenzylidene)-1,4-phenylene diamine (DHBPD) and TiO₂ nanoparticles prepared by a simple and rapid method for the determination of hydrazine (HZ) was described. In the first part of the work, cyclic voltammetry was used to investigate the redox properties of this modified electrode at various solution pH values and at various scan rates. A linear segment was found with a slope value of about 48 mV/pH in the pH range 2.0–12.0. The apparent charge transfer rate constant (k _s) and transfer coefficient (α) for electron transfer between DHBPD and TiO₂ nanoparticles-modified carbon paste electrode were calculated. In the second part of the work, the mediated oxidation of HZ at the modified electrode was described. It has been found that under optimum condition (pH 8.0) in cyclic voltammetry, a high decrease in overpotential occurs for oxidation of HZ at the modified electrode. The values of electron transfer coefficients (α) and diffusion coefficient (D) were calculated for HZ, using electrochemical approaches. Differential pulse voltammetry exhibited a linear dynamic range from 1.0 × 10⁻⁸ to 4.0 × 10⁻⁶ M and a detection limit (3σ) of 9.15 nM for HZ. Finally, this method was used for the determination of HZ in water samples, using standard addition method.     

Electrocatalytic oxidation of quinine sulfate at a multiwall carbon nanotubes-ionic liquid modified glassy carbon electrode and its electrochemical determination

The electrocatalytic oxidation of quinine sulfate (QS) was investigated at a glassy carbon electrode, modified by a gel containing multiwall carbon nanotubes (MWCNTs) and room-temperature ionic liquid of 1-Butyl-3-methylimidazolium hexafluorophate (BMIMPF₆) in 0.10 M of phosphate buffer solution (PBS, pH 6.8). It was found that an irreversible anodic oxidation peak of QS with E _pa as 0.99 V appeared at MWCNTs-RTIL/glassy carbon electrode (GCE). The electrode reaction process was a diffusion-controlled one and the electrochemical oxidation involved two electrons transferring and two protons participation. Furthermore, the charge-transfer coefficient (α), diffusion coefficient (D), and electrode reaction rate constant (k _f) of QS were found to be 0.87, 7.89 × 10⁻³ cm²⋅s⁻¹ and 3.43 × 10⁻² s⁻¹, respectively. Under optimized conditions, linear calibration curves were obtained over the QS concentration range 3.0 × 10⁻⁶ to 1.0 × 10⁻⁴ M by square wave voltammetry, and the detection limit was found to be 0.44 μM based on the signal-to-noise ratio of 3. In addition, the novel MWCNTs-RTIL/GCE was characterized by the electrochemical impedance spectroscopy and the proposed method has been successfully applied in the electrochemical quantitative determination of quinine content in commercial injection samples and the determination results could meet the requirement.     

Kinetics and mechanism of coal flotation

 The flotation kinetics of coarse coal particles was studied in a modified version of the Hallimond tube at 25 °C using nitrogen as the carrier gas, in the pH range 2–12. The kinetics was followed by measuring the volume of the particles accumulated in the collector tube as a function of time. At each pH, the rate constants were determined at several buffer concentrations and were extrapolated to zero buffer concentration. The observed first-order rate constant was represented as the product of separable constants and functions such as f _D, f _V and f _pH, which depend only on the particle size, gas flow and the pH of the dispersion, respectively. The diameter, D, of the particles was in the range 505–127 μm. The observed rate constant decreased linearly with the diameter of the particles at constant flow and it was calculated that f _D=exp(−1.56D). The dependence of f _V on the flow is a consequence of the fact that the flotation occurs when a single particle is captured by two bubbles. f _V was shown to be independent of the particle diameter. The effect of the pH on the rate of flotation was considered as resulting from the adsorption of protons (or hydroxide ions) by the particles and bubbles through multiple equilibria, assuming that there is no interaction between the binding sites. The pH–rate profile showed that there were two species responsible for the flotation: one stable at pH below 5 and the other at high pH. Comparison of f _V, f _D and f _pH for the flotation of coal and pyrite allowed the prediction of the optimum conditions for the separation of mixtures of these particles by flotation. Received: 6 August 2001  Accepted: 19 September 2001     

Taylor dispersion in systems of sedimenting nonspherical Brownian particles : II. Homogeneous ellipsoidal particles

An Aris-type moment scheme is applied to calculate the Taylor-Aris dispersion tensor for the sedimentation of small homogeneous ellipsoidal (and other orthotropic) particles settling under the influence of gravity in a quiescent viscous fluid and undergoing rotational and translational Brownian motions. This generalizes to triaxial particles a prior dispersion result for centrally symmetric bodies of revolution, such as spheroids. An independent Langevin-type dispersivity calculation is shown to yield results identical to those obtained by the moment scheme. The components and of the transversely isotropic dispersion dyadic, parallel and perpendicular, respectively, to the direction of the gravitational field, are shown to be given by the Taylor—Aris-type formulasHere, is the mean settling velocity of the particle, and and

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and (d₁,d₂,d₃) respectively the appropriate diffusivity components along the principal axes of the particle. The dimensionless coefficient γ, which is of order unity, is given by the formulaThis anisometric parameter vanishes identically for spherical particles and other hydrodynamically isotropic particles (e.g., cubes, tetrahedra, octahedra, etc.) whose translational and rotational hydrodynamic resistances are independent of the orientation of the particle relative to the directions of its linear and angular velocity vectors. Upon utilizing the translational and rotational Stokes-Einstein equations, explicit numerical values of and are furnished for ellipsoids of revolution of various aspect ratios and sizes when settling in water. Physical restrictions pertaining to sedimentation-vessel apparatus size and the requirement of reasonable sedimentation times greatly restrict the range of particle sizes whose anisometric properties may be experimentally investigated by this new particle-shape characterization technique.