Mass-mobility characterization of flame-made ZrO2 aerosols: Primary particle diameter and extent of aggregation

Gas-borne nanoparticles undergoing coagulation and sintering form irregular or fractal-like structures affecting their transport, light scattering, effective surface area, and density. Here, zirconia (ZrO₂) nanoparticles are generated by scalable spray combustion, and their mobility diameter and mass are obtained nearly in situ by differential mobility analyzer (DMA) and aerosol particle mass (APM) measurements. Using these data, the density of ZrO₂ and a power law between mobility and primary particle diameters, the structure of fractal-like particles is determined (mass-mobility exponent, prefactor and average number, and surface area mean diameter of primary particles, d_va). The d_va determined by DMA-APM measurements and this power law is in good agreement with the d_va obtained by ex situ nitrogen adsorption and microscopic analysis. Using this combination of measurements and above power law, the effect of flame spray process parameters (e.g., precursor solution and oxygen flow rate as well as zirconium concentration) on fractal-like particle structure characteristics is investigated in detail. This reveals that predominantly agglomerates (physically-bonded particles) and aggregates (chemically- or sinter-bonded particles) of nanoparticles are formed at low and high particle concentrations, respectively.     

Thermal aggregation of bovine serum albumin studied by asymmetrical flow field-flow fractionation

The use of asymmetrical flow field-flow fractionation (AsFlFFF) in the study of heat-induced aggregation of proteins is demonstrated with bovine serum albumin (BSA) as a model analyte. The hydrodynamic diameter (d_h), the molar mass of heat-induced aggregates, and the radius of gyration (R_g) were calculated in order to get more detailed understanding of the conformational changes of BSA upon heating. The hydrodynamic diameter of native BSA at ambient temperature was ∼7 nm. The particle size was relatively stable up to 60 °C; above 63 °C, however, BSA underwent aggregation (growth of hydrodynamic diameter). The hydrodynamic diameters of the aggregated particles, heated to 80 °C, ranged from 15 to 149 nm depending on the BSA concentration, duration of incubation, and the ionic strength of the solvent. Heating of BSA in the presence of sodium dodecyl sulfate (1.7 or 17 mM) did not lead to aggregation. The heat-induced aggregates were characterized in terms of their molar mass and particle size together with their respective distributions with a hyphenated technique consisting of an asymmetrical field-flow fractionation device and a multi-angle light scattering detector and a UV-detector. The carrier solution comprised 8.5 mM phosphate and 150 mM sodium chloride at pH 7.4. The weight-average molar mass (M_w) of native BSA at ambient temperature is 6.6 × 10⁴ g mol⁻¹. Incubation of solutions with BSA concentrations of 1.0 and 2.5 mg mL⁻¹ at 80 °C for 1 h resulted in aggregates with M_w 1.2 × 10⁶ and 1.9 × 10⁶ g mol⁻¹, respectively. The average radius of gyration and the average hydrodynamic radius of the heat-induced aggregate samples were calculated and compared to the values obtained from the size distributions measured by AsFlFFF. For comparison static light scattering measurements were carried out and the corresponding average molar mass distributions of solutions with BSA concentrations of 1.0 and 2.5 mg mL⁻¹ at 80 °C for 1 h gave aggregates with M_w 1.7 × 10⁶ and 3.5 × 10⁶ g mol⁻¹, respectively.     

Effects of redox conditions and zinc(II) ions on metallothionein aggregation revealed by chip capillary electrophoresis

Metallothioneins (MTs) belong to cysteine-rich proteins with unique higher structure. One of the most known MT's functions is metals detoxification and maintaining their homeostasis in a cell. Structure of MT with naturally occurred zinc(II) ions can be affected by concentration of metal ions as well as redox milieu inside a cell, however the exact explanation and biochemical effects of the structural changes are still missing. In this study we used capillary electrophoresis on chip coupled with fluorescence detection to determine structural changes of MT with increasing concentration of zinc(II) ions and under various redox conditions. To investigate the structural-dependent effects, reduced and/or oxidized apo-MT (MT without natural occurred metal ion) was prepared. Zinc binding into reduced and/or oxidized apo-MT was compared. MT was incubated with 0, 5, 15, 25, 50 and 100 μM ZnCl₂ for 1 h in 37 °C. Formation of MT aggregates with increasing zinc concentration was observed by spectrophotometry, chip capillary electrophoresis, and SDS-PAGE. We found out that reduced MT forms aggregates more readily compared to oxidized MT. Using the chip capillary electrophoresis allowed us relative quantification of MT aggregation as a decrease in the area of the signal corresponding to the monomer form of MT (Mw 15 kDa, migration time 26.5 s) and its ratio to total signal (sum of all signals measured by the electrophoresis). The dependences had an exponential character with equation y = 2.4 × e^−0.01x, R² = 0.945 for 15 kDa peak area and y = 0.11 × e^−0.01x, R² = 0.938 for decrease of 15 kDa peak area ratio to the total signal. Zn–MT interaction was 30% faster during the first 15 min and 50% faster during the whole experiment for reduced MT. It can be concluded that formation of MT aggregates is dependent on redox state and Zn(II) concentration.     

Novel thermoresponsive block copolymers having different architectures—structural,rheological, thermal,and dielectric investigations

Thermoresponsive block copolymers comprising long, hydrophilic, nonionic poly(methoxy diethylene glycol acrylate) (PMDEGA) blocks and short hydrophobic polystyrene (PS) blocks are investigated in aqueous solution. Various architectures, namely diblock, triblock, and starblock copolymers are studied as well as a PMDEGA homopolymer as reference, over a wide concentration range. For specific characterization methods, polymers were labeled, either by partial deuteration (for neutron scattering studies) or by fluorophores. Using fluorescence correlation spectroscopy, critical micellization concentrations are identified and the hydrodynamic radii of the micelles, r _h ^mic , are determined. Using dynamic light scattering, the behavior of r _h ^mic in dependence on temperature and the cloud points are measured. Small-angle neutron scattering enabled the detailed structural investigation of the micelles and their aggregates below and above the cloud point. Viscosity measurements are carried out to determine the activation energies in dependence on the molecular architecture. Differential scanning calorimetry at high polymer concentration reveals the glass transition of the polymers, the fraction of uncrystallized water and effects of the phase transition at the cloud point. Dielectric relaxation spectroscopy shows that the polarization changes reversibly at the cloud point, which reflects the formation of large aggregates upon heating through the cloud point and their redissolution upon cooling.     

Gas transport in TiO2 nanoparticle-filled poly(1-trimethylsilyl-1-propyne)

Titanium dioxide (TiO₂) nanoparticles were dispersed via solution processing in poly(1-trimethylsilyl-1-propyne) (PTMSP) to form nanocomposite films. Nanoparticle dispersion was investigated using atomic force microscopy and transmission electron microscopy. At low-particle loadings, nanoparticles were dispersed individually and in nanoscale aggregates. At high-particle loadings, some nanoparticles formed micron-sized aggregates. The gas transport and density exhibited a strong dependence on nanoparticle loading. At low-TiO₂ loadings, the composite density was similar to or slightly higher than that predicted by a two-phase additive model. However, at particle loadings exceeding approximately 7 nominal vol.%, the density was markedly lower than predicted, suggesting that the particles induced the creation of void space within the nanocomposite. For example, when the TiO₂ nominal volume fraction was 0.35, the polymer/particle composite density was 40% lower than expected based on a two-phase additive model for density. At low-nanoparticle loading, light gas permeability was lower than that of the unfilled polymer. At higher nanoparticle loadings, light gas permeability (i.e., CO₂, N₂, and CH₄) increased to more than four times higher than in unfilled PTMSP. At most, selectivity changed only slightly with particle loading.     

Effect of viscosity of a liquid membrane containing oleyl alcohol on the pertraction of butyric acid

Solvent formulation is important in the optimization of the mass-transfer through supported liquid membranes (SLM) in pertraction and membrane extraction. Oleyl alcohol (OA) is frequently used as the solvent or diluent in the extraction of carboxylic acids. A disadvantage of OA is its relatively high viscosity of 28.32 mPa s at 25°C. This can be decreased by the application of a less viscous OA diluent, e.g. dodecane. The relationship between the ratio of the distribution coefficient of butyric acid (BA), D _F, and the viscosity of OA-dodecane solvents, µ, as extraction and transport characteristics, and the overall mass-transfer coefficient, K _p, through SLMs was analyzed. Dependence of the D _F/µ ratio on the OA concentration showed a maximum at the OA concentration of 15 mass % to 30 mass %. The OA concentration dependence of K _p for SLMs exhibited also a maximum at about 30 mass % and 20 mass % of OA at the BA concentration driving force of 0.12 kmol m^?3 and 0.3 kmol m^?3, respectively. Shifting of the maximum in K _p dependences towards lower OA concentrations by increasing the BA concentration driving force is in agreement with the D _F/µ ratio dependence. Using pure OA as the solvent or diluent is not preferable and a mixture of a low viscosity diluent with the OA concentration below 40 mass % should be used. The presented results show the potential of the D _F/µ ratio in the screening and formulation of solvents in extraction and SLM optimization.     

The strong influence of alkyl tail length on the aggregation and viscoelasticity of carboxylate gemini surfactants with a p-dibenzenediol spacer in aqueous solution

This paper reports a study on the aggregation and rheological behavior of the family of O, O’-bis(sodium 2-alkylcarboxylate)-p-dibenzenediol (referred to as C_m?₂C_m, m?=?10, 12, 14, respectively) in aqueous solution using dynamic light scattering, ¹H NMR and rheology measurements. The results showed that all three surfactants formed large network-like aggregates at low concentrations. However, C₁₀?₂C₁₀ formed small compact micelles simultaneously but neither C₁₂?₂C₁₂ nor C₁₄?₂C₁₄ did. These network-like aggregates were transformed into the wormlike micelles with increasing the surfactant concentration. The length of alkyl tails was found to strongly affect the viscoelasticity of wormlike micellar solutions. From C₁₀?₂C₁₀, C₁₂?₂C₁₂ to C₁₄?₂C₁₄ in turn, the system developed rapidly from the viscous fluid to typically viscoelastic solution and then to a solid-like gel. The scaling exponents of the concentration dependence of both zero-shear viscosity (η ₀) and plateau elastic modulus (G′_∞) greatly exceeded the theoretic predictions, showing fast micellar growth and strong entanglements between the wormlike micelles. For C₁₄?₂C₁₄ that had the longest alkyl tails in this series, the wormlike micelles formed at 140?mmol L^?1 were quite long and the micellar reptation dominated over the scission and recombination. This system yielded a viscosity as high as 2.20?×?10⁴ Pa?s at 25 °C.     

Dynamic light scattering and rheology studies of aqueous solutions of amphiphilic sodium maleate containing copolymers

Light scattering techniques, video particle‐tracking microrheology, and bulk rheology were employed to examine the structure and dynamics of a series of alternating sodium maleate copolymers with moderately hydrophobic comonomers (diisobutylene, styrene, and isobutylene) in aqueous solutions. The scaling dependence of the specific viscosity (η_sp) on the polyelectrolyte concentration (c) was studied with and without added salt; similar trends were found in both conventional rheology and particle‐tracking microrheology measurements, showing good performance of the technique with flexible polyelectrolytes. Furthermore, with dynamic light scattering performed in high added salt conditions, we examined the behavior of the amplitude of the fast mode, which is in agreement with scaling predictions. In contrast, the slow modes are not understood and display three separate behaviors for the wavevector q dependence of the decay rate (Γ), depending on the comonomer; superdiffusive (Γ ～ q^2.7, isobutylene) possibly because of sticky aggregates, wavevector independent (Γ ～ q⁰, styrene) most likely because of coupled polyion‐ion diffusion and diffusive (Γ ～ q^2.0, diisobutylene) presumably because these aggregates are not sticky. The hydrophobicity of the comonomer appears to switch the aggregation process between “open,” “closed,” and “non” association for isobutylene, diisobutylene, and styrene respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 774–785, 2007     

Kinetics of cluster aggregation in competition with a chemical growth reaction

The kinetics of abundances and the distribution in size of clusters at a given time are obtained by numerical simulation in the case where a chemical growth competes with the coalescence of clusters originating from isolated monomers. To take into account the size dependence of cluster reactivity, it is assumed that the chemical reaction occurs only beyond a critical valuen _c . The kinetics of the total cluster concentration are unchanged by addition of the reactant but the size distribution is suddenly perturbed for sizes beyondn _c . The decay of the reactant, the kinetics of a cluster of a given nuclearity and the distribution of sizes at a given time depend on the relative values of the rates of coalescence and of growth due to the reactant. It is shown how the initial conditions control the kinetics and the amplitude or the time of the maximum cluster abundance. The case of an attack by a chemical reactant on clusters, restricted to low values ofn, is also considered. The concentration kinetics (for all size clusters) display much lower amplitudes than for pure coalescence case. No parity effects are observed.     

Effect of the degree of deacetylation and the substitution of carboxymethyl chitosan on its aggregation behavior

The aggregation behavior of carboxymethyl chitosan (CM‐chitosan) with various degrees of deacetylation (DD) and substitution (DS) was characterized with viscometry, gel permeation chromatography (GPC), and GPC coupled with laser light scattering (GPC‐LLS). The results indicate that CM‐chitosan has a strong tendency to form aggregates in aqueous solution and the aggregation behavior depends on DD and DS values. The apparent aggregation number (N_ap), the gyration radius (R_g), and the weight fraction of the aggregates (F_a) reached maximum at a DD value of 50%, then decreased, with the DD value deviating from 50%. A higher DS value helped to form aggregates; when the DS value increased from 0.65 to above 1.0, N_ap and R_g increased sharply. The dependence of the refractive index increment (dn/dc) on the DD and DS values was related to variation of the charge density and the hydrophobic interaction along the molecular chains. The conformations of CM‐chitosan aggregates were studied by the LLS method. The aggregates showed a spherical shape, and the chain stiffness increased with introduction of the acetyl groups. The DS value had no clear influence on the chain conformation that was observed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 296–305, 2005     

Molecular mass concentrations for a powdered SRM sample using a quantitative single particle analysis

In a quantitative single particle analysis, named the low-Z particle EPMA, number concentration data for chemical species encountered in aerosol sample are provided. However, it will be more useful if mass concentration data can be obtained from single particle analysis; i.e., the single particle analysis data for weight fractions of chemical species can be complementarily used in combination with the bulk analysis data, for more clearly understanding the behavior of airborne aerosols. In order to investigate how reliably mass concentration data can be obtained from the low-Z particle EPMA technique, a potassium feldspar powdered standard reference material (SRM), of which elemental weight fractions are well defined by various bulk analytical techniques, was analyzed using the low-Z particle EPMA technique. In this work, it is demonstrated that weight fractions of major elements in the powdered SRM sample obtained by the low-Z particle EPMA are within 8% to the certified values obtained by bulk analytical techniques, although the single particle and bulk analyses employ different approaches. Further, it is shown that the quantitative single particle analysis, i.e., low-Z particle EPMA, can provide molecular mass concentration data for chemical species, which is not easy to obtain using bulk analysis.     

Viscosity of liquid suspensions with fractal aggregates: Magnetic nanoparticles in petroleum colloidal structures

New physical model is presented resulting in a simple formula for the dependence of viscosity η of colloidal liquid solution on the shear rate G applicable to a wide variety of systems including complex natural liquids like petroleum. The principal point of the model is the fractal nature of colloid particle aggregates present in the liquid. Such aggregates are experimentally detected now in non-Newtonian liquids. The model is based on calculation of energy loss on colloidal particle aggregate of fractal structure localized in the flow of liquid with shear rate. We have performed the viscosity measurement experiments which confirmed successfully the developed physical model. Also, we demonstrate experimentally that petroleum colloidal particles and magnetic iron oxide nanoparticles can form composite fractal-like aggregates in natural petroleum materials. Our model can explain both the non-Newtonian properties of petroleum and sensitivity of petroleum viscosity to external magnetic fields.     

Langmuir aggregation of Evans blue on cetyltrimethylammonium bromide and on proteins and its application

The microphase adsorption-spectral correction (MPASC) technique is described and applied to the study of the interactions of Evans blue (EB) with cetyltrimethylammonium bromide (CTAB) and with four proteins: bovine serum albumin (BSA), myoglobin (Mb), hemoglobin (Hb) and ovalbumin (OVA). EB can be adsorbed on a cationic surfactant and on protein by electrostatic force and the aggregation obeys the Langmuir isotherm. Results have shown that the products are formed as follows: monomer aggregate EB·CTAB, micellar aggregate (EB·CTAB)₇₈ and protein aggregates (EB₆₈·BSA), (EB₁₄·OVA), (EB₁₂₆·Mb) and (EB₅₈·Hb). The adsorption constant of the aggregates are calculated to be K_EB·CTAB=2.95×10⁶, K_EB68·BSA=3.40×10⁴, K_EB14·OVA=5.20×10², K_EB126·Mb=6.81×10² and K_EB58·Hb=5.73×10², respectively. The aggregation of EB in proteins is sensitive in the presence of CTAB and selective in the presence of EDTA and it has been applied to the analysis of samples with satisfactory results.     

Effects of the thermal history and concentration on the aggregation of Erwinia gum in an aqueous solution

The aggregation of Erwinia (E) gum in a 0.2 M NaCl aqueous solution was investigated by multi‐angle laser light scattering and gel permeation chromatography (GPC) combined with light scattering. The GPC chromatograms of five fractions contained two peaks; the fractions had the same elution volume but different peak areas, suggesting that aggregates and single chains coexisted in the solution at 25 °C. The apparent weight‐average molecular weights (M_w) of the aggregates and single chains for each fraction were all about 2.1 × 10⁶ and 7.8 × 10⁴, respectively. This indicates that the aggregates were composed of about 27 molecules of E gum in the concentration range used (1.0 × 10⁻⁶ to 5.0 × 10⁻⁴ g/mL). The weight fraction of the aggregates (w_ag) increased with increasing concentration, but the aggregates still existed even in an extremely dilute solution. The fractionation process and polymer concentration hardly affected the apparent aggregation number but significantly changed w_ag. The E‐gum M_w decreased sharply with an increase in temperature. When the E‐gum solution was kept at 100 °C, w_ag decreased sharply for 20 h and leveled off after 100 h. Once the aggregates were decomposed at a higher temperature, no aggregation was observed in the solution at 25 °C, indicating that the aggregation was irreversible. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1352–1358, 2000     

Structure of the CO bond on supported Pd particles: influence of size and surface state

We have investigated the surface of supported palladium particles by static secondary ion mass spectrometry (SSIMS). Pd particles were grown in situ on alumi na (oxide layer and sapphire surfaces) and stabilized by heating treatment. The particle size, density and crystallographic structure were determined in previous studies by transmission electron microscopy and diffraction (TEM and TED). Various ionic species are detected by SSIMS analysis which makes it possible to characterize the CO absorbed layer: Pd _n CO⁺ (n=1, 2) for molecular adsorption and Pd _n C⁺ for CO dissociation. The size dependence of the bonding state of CO (linear, bridge, ...) was monitored by: PdCO⁺/σ _n Pd _n CO⁺ signal ratio over various size particles (mean diameter in the 2–9 nm range). Investigations were performed as a function of CO coverage (adsorption at room temperature) and also under CO dissociation conditions: heating under CO atmosphere or CO+O₂ (catalysis). The data analysis shows that on clean Pd particles smaller than 3 nm the CO molecules give rise mainly to PdCO⁺ species. We have interpreted this result by the adsorption of CO on two palladium atoms, the carbon end being tightly bonded to a low coordination Pd atom and the oxygen end weakly bonded to a neighbour Pd atom. These couples of Pd atoms form the specific sites for CO dissociation, the density of which depends on the roughness of the particle surface.     

Extraction kinetics of lanthanum(III), uranyl(VI), and thorium(IV) nitrates from water-salt solutions using a composite based on a polymeric support and tri-n-butyl phosphate at various temperatures

The extraction kinetics of lanthanum(III), uranyl(VI), and thorium(IV) nitrates from water-salt solutions using a composite based on a polymeric support and tri-n-butyl phosphate (TBP) were studied at 293.15–333.15 K. Interfacial diffusion (the film kinetics) is the rate-controlling stage of extraction. Mass transfer coefficients were determined, and their temperature dependence was used to estimate apparent activation energies E _a. The mass transfer coefficients increase in going from lanthanum(III), uranyl(VI), and thorium(IV) nitrate solutions to water-salt solutions containing 2 mol/L sodium nitrate or with rising temperature. E _a is independent of the metal ion and the supporting electrolyte concentration; E _a = 25 ± 1 kJ/mol. At a fixed temperature, the increasing order of the mass transfer coefficients is as follows: thorium(IV) < uranyl(VI) < lanthanum(III).     

Measurement of the association constants through micro-Raman spectra of supersaturated lithium perchlorate droplets

High quality micro-Raman spectra of the LiClO4droplet with mass of nanogram scale were obtained at various concentrations from dilute to supersaturated state.From component band analysis of the v1-ClO4band,four peaks at 933.3,936.8,942.1 and950.7 cm 1were identified and assigned to free solvated perchlorate anion,solvent-shared ion pair,contact ion pair and complex ion aggregates,respectively.As expected,the signature of free solvated ClO4ion was observed to decrease in intensity with the increase in concentration.The intensity of the signature from solvent-shared ion pair was observed to rise with increase in concentration from 1.8 mol/kg to 5.0 mol/kg before decreasing as the concentration was further increased to 5.6mol/kg.Signatures of contact ion pair and of complex ion aggregates were shown to increase as the concentration was enhanced.Based upon the Eigen mechanism,we show that three association equilibria can be used to describe the transformations between free solvated perchlorate anion,solvent-shared ion pair,contact ion pair and complex ion aggregates.The overall association constant,K,and the stepwise association constants Ki(i=1 to 3)in the Eigen mechanism were determined separately with values of 0.025±0.003,0.023±0.002,0.068±0.033 and 0.686±0.174.Based on these constants,the electronic performance can be reasonably predicted by the optimum choice of electrolyte concentrations.     

Mass Spectrometry Study of Multiply Negatively Charged, Gas-Phase NaAOT Micelles: How Does Charge State Affect Micellar Structure and Encapsulation?

We report the formation and characterization of multiply negatively charged sodium bis(2-ethylhexyl) sulfosuccinate (NaAOT) aggregates in the gas phase, by electrospray ionization of methanol/water solution of NaAOT followed by detection using a guided-ion-beam tandem mass spectrometer. Singly and doubly charged aggregates dominate the mass spectra with the compositions of [Na_n-zAOT_n]^z– (n?=?1–18 and z?=?1–2). Solvation by water was detected only for small aggregates [Na_n-1AOT_nH₂O]^– of n?=?3–9. Incorporation of glycine and tryptophan into [Na_n-zAOT_n]^z– aggregates was achieved, aimed at identifying effects of guest molecule hydrophobicity on micellar solubilization. Only one glycine molecule could be incorporated into each [Na_n-zAOT_n]^z– of n?≥?7, and at most two glycine molecules could be hosted in that of n?≥?13. In contrast to glycine, up to four tryptophan molecules could be accommodated within single aggregates of n?≥?6. However, deprotonation of tryptophan significantly decrease its affinity towards aggregates. Collision-induced dissociation (CID) was carried out for mass-selected aggregate ions, including measurements of product ion mass spectra for both empty and amino acid-containing aggregates. CID results provide a probe for aggregate structures, surfactant-solute interactions, and incorporation sites of amino acids. The present data was compared with mass spectrometry results of positively charged [Na_n+zAOT_n]^z+ aggregates. Contrary to their positive analogues, which form reverse micelles, negatively charged aggregates may adopt a direct micelle-like structure with AOT polar heads exposed and amino acids being adsorbed near the micellar outer surface.