Liquid Nebulization-Ion Mobility Spectrometry Based Quantification of Nanoparticle-Protein Conjugate Formation.

Low pressure (<20 Torr) non-thermal plasma flow tube reactors are commonly used for the synthesis of high purity nanoparticles (NPs) via nucleation and subsequent growth from vapor phase precursors. In spite of their utility, process monitoring (i.e. output NP size characterization) in such reactors is difficult, as there is a dearth of techniques available for online NP size distribution function measurement. In this study, we developed and applied an ion mobility spectrometry (IMS) system consisting of a low pressure differential mobility analyzer (LPDMA) and electrical detector to determine the collision cross section distribution functions of Si NPs synthesized in a radio frequency non-thermal SiH4–Ar plasma operated at ∼2 Torr (266 Pa). The collision cross section, roughly proportional to projected area, is a parameter quantifying the size and structure of nanometer scale species in the vapor phase. We introduce the collision cross section distribution function as a metric for potential use in online process monitoring in NP synthesis. Proper inversion of the collision cross section distribution function requires a priori knowledge of the LPDMA transfer function. We utilized a tandem differential mobility analyzer approach, coupled with a Twomey–Markwoski based scheme to determine LPDMA transfer functions. Subsequent application of these transfer functions in collision cross section distribution function determination showed that at the outlet of the non-thermal plasma flow tube reactor, both negatively and positively charged Si NPs persisted with nearly identical collision cross section distribution functions. NPs were found to have mode ‘mobility equivalent’ diameters near 10 nm, and via TEM analysis were found to persist at the reactor outlet as small aggregates composed of ∼5 nm diameter primary particles. Size distribution functions inferred from collision cross section measurements were compared to size distribution functions inferred from TEM images; excellent agreements were found between IMS and TEM for both mean mobility equivalent diameter and distribution function width. In total, this study shows that (1) IMS is a viable approach for process monitoring in non-thermal plasma NP flow tube synthesis systems, (2) although NPs are modestly aggregated at low-pressure plasma reactor outlets, the extent of aggregation is considerably less than observed in most atmospheric pressure and equilibrium NP synthesis systems (e.g. flames), and (3) after exiting the plasma reactor, the decharging of NPs from highly negative charge levels to a bipolar charge distribution likely drives aggregation on the plasma boundary.

Evaluation of assumptions made by Hygroscopic Tandem Differential Mobility Analyzer inversion routines

The fractal characteristics of attenuation are evaluated, and an attempt is made to establish an alternative theoretical model for ultrasonic scattering at grain boundaries. The theoretical development starts with attenuation scaled by wavelength and an inverse power law expression for the grain size distribution function. The wavelength dependence of the attenuation is found to be also an inverse power law with the same exponent as the grain size distribution function. Theoretical justifications for such a size distribution are given, as well as the representation of a 3-D self-similar size distribution in a 2-D image.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The results of the investigation of the performance characteristics of two-fluid nozzle (a type of simple pneumatic nozzle) are shown in this paper. A comparison of the drop-size distribution from mentioned nozzle with different construction characteristics at different gas flow and feed rates showed that nozzle characteristics had a considerable influence on drop-size distribution for the conditions studied. Studies were carried out of the effect of nozzle internal diameter, exit orifices’ diameters, feed rate and gas pressure on droplet size distribution. In all experiments performed, air has been used as a gas phase (volume flow rate Va = 0.8 - 1.6 dm3/s according to air pressure pa = 1.375 - 2.5 bar), and 3% solution of nigrosine in water (mass flow rate mw = 0.26 - 1.07 kg/s) as a liquid phase. After detailed analysis of existing droplet sampling techniques, immersion sampling technique was accepted. Solution was sprayed into small cells, with glass bottom, filled with kerosene, positioned at the several distances from the nozzle. Results obtained were processed using different size distribution functions (experimental: Nukiyama-Tanasawa, Rosin-Rammler, Mugele-Evans, and theoretical: Gaussian, logarithmic, Gamma, etc.), by calculating adequate parameters for each distribution function. The most appropriate agreement of experimental results was obtained by Nukiyama-Tanasawa and Gamma size distribution functions. The Sauter mean diameter was also calculated and compared with the same diameter obtained from different size distribution functions. An equation is recommended for estimation of droplet size (Sauter mean diameter) under different nozzle working conditions.

Air parcels in the marine boundary layer (MBL) are mixed up through nonprecipitating clouds at the top of the MBL many times (on average) before they can be removed by precipitation scavenging. The equivalent dry size of the particles (cloud condensation nuclei, CCN) upon which droplets are formed increases because of liquid phase oxidation of soluble trace gases during the cloud processing. The observed separation of the submicron size distribution into an interstitial mode and cloud droplet residue mode makes it possible to infer the effective MBL cloud supersaturation and cloud droplet concentrations from surface measurements of the aerosol size distribution during periods when nonprecipitating MBL clouds are present in the back trajectory and the MBL is well mixed. The effect of particle composition on the accuracy of the inferred cloud supersaturations is evaluated. A large database of hundreds of size distributions taken on an Atlantic and a Pacific cruise and an airship flight off the Oregon coast are used to calculate the range of effective MBL cloud supersaturations and droplet concentrations encountered during these expeditions. The inferred droplet concentrations on the Pacific cruise were mostly in the 25 to 150 cm−3 range, whereas they were mostly in the 50 to 500 cm−3 range for the Atlantic cruise. The inferred effective supersaturation in the tropical MBL clouds was typically in the 0.15% to 0.25% range. Recent work of Tang and Munkelwitz [1994] would indicate that particles consisting of mixtures of ammonium sulfate and sulfuric acid would not have recrystalized in the differential mobility analyzer (DMA) within the range of relative humidities (45% to 60%) at which the DMA was operated. At these humidities the hydrated size can be as much as 20% greater than the dry size. Corrections for the hydrated size within the DMA at the time of measurement are included and are also used to correct previous measurements of the relationship between dry size and critical supersaturation made using the Naval Research Laboratory (NRL) DMA and NRL thermal gradient CCN counters.

The concentration and size distribution of particles from 0.001 to 3 μ in radius dispersed in the urban atmosphere was measured with a continuous-sampling sizing system composed of a nuclei counter, an electrical particle-counter, and an optical counter. Atmospheric aerosol size distribution measurements made by previous investigators are reviewed and compared with the new information. The diurnal variation of size distribution was measured for four 24-hr periods, and concentration variations are shown to be related to local particulate source and meteorological conditions. The self-preserving size distribution theory of Friedlander is reviewed and tested with 58 size distributions measured under a variety of conditions. The experimental data are consistent with the theory for particles of radii greater than about 0.05 μ, and the size distribution function, dN/dr, is found to he equal to 0.05ϕr−4 for the size range 0.05–3 μ where N is the number of particles cm−3, r the particle radius, and ϕ the particle volume per unit volume of aerosol. A good approximation to the size distribution of atmospheric aerosol for particles greater than 0.05 μ is shown to result from determining ϕ from the weight of high-volume filter samples and the particle density.

The energy stored as free radicals in the process of growth and photoprocessing of interstellar grain mantles by ultraviolet radiation in clouds is treated as the primary cause of both grain mantle destruction and gas molecule production in dark clouds. The triggering mechanism for energy release is provided by grains colliding with each other as a result of turbulence in the cores of the clouds. A quantitative derivation of a size distribution function of the general form -α3a3 e for the mantles of the core-mantle interstellar dust grains, which best determines simultaneously the mean interstellar extinction and polarization curves, is based on the dust-dust collision rate and a grain evaporation efficiency parameter, f, to be determined by experiments performed in the photochemistry laboratory at Leiden University. The same mantle destruction process which produces the size distribution function is used to provide a numerical estimate of molecule ejection into the gas phase in terms of a parameter, αM, the effective molecule concentration fraction in the evaporating mantle. The evaporation efficiency factor and the molecule concentration function required in the derivations to give a simultaneously consistent picture of the mean size distribution function and the molecule production rate, specifically for H2CO, may be inferred to be realistic representations of the laboratory results obtained to date. The molecules ejcted by the explosive process are likely to appear in initially excited states and would be subject to subsequent gas phase interactions.

Previous work on the measurement of aerosol size distribution functions (SDFs) by laser extinction mainly relied on light sources from a relatively narrow wavelength range. This paper investigates the potential advantages of extending the extinction method to a general wavelength-multiplexed laser extinction (WMLE) concept by incorporating an arbitrary number of laser sources from a wider wavelength range. This extension improves the sensitivity of SDF measurements over wider aerosol diameter ranges and enables a stable algorithm to invert the extinction data to obtain SDFs. These advantages are illustrated by an example WMLE scheme employing wavelengths in the spectral range from 0.25 to 10μm to measure SDFs of water aerosols. Application of this approach to other aerosol systems is also considered. The WMLE scheme was found to provide stable determination of a variety of SDFs with Sauter mean diameters ranging from sub-micron to about 10μm. The sensitivity of such determinations was evaluated to reveal the optimum applicable range of the wavelengths employed. The analyses performed here provide theoretical background and motivation for practical applications of the WMLE concept.

Performance check of particle size standards within and after shelf-life using differential mobility analyzer

This work is devoted to the numerical modeling of highly polydisperse granular materials in view of investigating the texture and mechanical behavior in quasi‐static shearing. The polydispersity is modeled in terms of size span and curvature of the particle size distributions. A method is proposed to generate representative size distributions both in number and volume of size classes, and the accessible polydispersity parameters are determined for tractable number of particles. A geometrical method is used to construct large samples and to study the resulting texture in a systematic manner as a function of size distribution. These samples are then subjected to simple shear with periodic boundary conditions by means of the contact dynamics method. We show that: 1) The highest level of solid fraction corresponds to uniform distribution by particle volume fractions; 2) The shear strength in the steady state is independent of polydispersity; 3) A detailed analysis of the texture and force transmission indicates that this property results from the mutual compensation between the anisotropies of contact orientations and branch‐vector lengths, and also from the fact that the strong force chains are mainly captured by the largest particles; 4) In the presence of adhesion between particles, the Coulomb cohesion increases with size span.

The controlled splashing of metal droplets plays a decisive role in the kinetics of the basic oxygen furnace (BOF) process. In this work, a mathematical model was developed for predicting the size distribution of spherical droplets ejected at an impingement zone. Harmonic oscillators are used to describe the ejection sites, and the upper limit for the droplet population is calculated through a force balance. The model was validated against literature data from high-temperature crucible experiments involving different supply pressures and lance heights as well as both single-hole and multihole lances. The predicted size distribution of the metal droplets was found to be in good agreement with the droplet size distributions measured from outside the crucible. The model was also applied for predicting the size distribution parameters of the Rosin–Rammler–Sperling (RRS) size distribution function. The model developed is computationally light and is suitable to be used as a part of offline and online simulation tools for the BOF process.

Ion mobility in the pharmaceutical industry: an established biophysical technique or still niche?

Predicting the effective thermal conductivity of polydispersed beds of softwood bark and softwood char ☆

Derivation of Size Distributions of Surfactant Micelles Taking into Account Shape, Composition, and Chain Packing Density Fluctuations

Semi-empirical model for indirect measurement of soot size distributions in compression ignition engines