A method to deposit a known number of polystyrene latex particles on a flat surface

Abstract

This study introduces a method to deposit polystyrene latex (PSL) particles on a silicon wafer in a manner that allows their number to be predicted with a high degree of accuracy. A laminar flow growth tube is used to condense supersaturated water vapor on seed aerosol particles that are water-insoluble. After condensation is complete the droplets are accelerated through a nozzle to form an aerosol jet, and the number of droplets in this jet is counted optically. The droplets are then deposited on a flat surface by inertial impaction. The particle number on the surface is predicted by multiplying the droplet number by an experimentally evaluated conversion coefficient of 0.991?±?0.011 (k?=?2). Uncertainty analysis showed with a 95% confidence interval that the particle number on a flat surface is ±?2.0%. The primary application of this method is to make a particle number standard (PNS) wafer whose intended use is to evaluate the counting efficiencies of wafer surface scanners, and this study demonstrates the fabrication of such PNS wafers. A motorized XY-stage moves the surface horizontally to deposit PSL particles along desired paths over a half-inch wafer. The particle number was varied over seven levels ranging from 10 to 10,000. The particle diameter was varied at four levels: 0.814, 0.18, 0.102, and 0.046?µm. In all PNS wafers, the number of deposited particles was counted using optical microscopes. The observed particle numbers were all within the 95% confidence interval of the predicted value.

Copyright © 2019 American Association for Aerosol Research     

Maximizing the singly charged fraction of sub-micrometer particles using a unipolar charger

Particle charging via the mixing of aerosols with unipolar ions typically results in multiple charges on particles. Particle classification and sizing, based on the electrical mobility, ideally requires all the particles being singly charged to the performance enhancement. In this study, we explored the feasibility of maximizing the singly charged fraction of particles via the control of the N_it product in a unipolar charger. The feasibility was first investigated by modeling unipolar diffusion charging. It was found that the singly charged fraction of monodisperse particles could be maximized by the control of the N_it product. A corona-based unipolar charger was also constructed to study the maximization of the singly charged fraction of monodisperse particles. It was found that a wider range of ion concentration in the charging zone could be obtained by the variation of ion-driving voltage compared to that by changing the corona-discharge current. The maximum singly charged fraction of monodisperse particles in various sizes was characterized when the charger was operated at the flow rates of 1.5 and 3.0 lpm. It was evidenced that the current charger could be conditioned to achieve a higher singly charged fraction of particles than that by bipolar chargers in the particle size range of 20–200?nm, particularly in the ultrafine particle size range. The control of N_it product in the charging zone of a unipolar charger offers a simple and effective means to enhance the singly charged fraction of particles in a given size range.

Copyright © 2019 American Association for Aerosol Research     

Determination of surface area and volume of nanoparticle aggregates deposited in the human respiratory tract using DMA data

A method is proposed for using size distribution data obtained with a differential mobility analyzer (DMA) to calculate the total surface area and volume of electrically conducting nanoparticle chain aggregates deposited in the human respiratory tract. The method consists of two steps: (1) the electrical mobility diameter of conducting aggregates determined with a DMA is used to calculate the diffusion-equivalent diameter and (2) the theory of idealized aggregates developed by Lall and Friedlander [(2006). On-line measurement of ultrafine aggregate surface area and volume distributions by electrical mobility analysis: I. Theoretical analysis. Journal of Aerosol Science 37, 260] is applied in calculations for the aggregate surface area and volume. The results of calculations using the volume distribution of a sample of diesel exhaust particles indicate that deposited aggregates have a larger total surface area than do electrical-mobility-equivalent spheres, even though the deposited aggregates have a much smaller total volume. The proposed method for calculating diffusion-equivalent diameter from electrical mobility diameter is also employed to show that the deposition data reported in literature for diesel exhaust particles and petrol particles agree well when the deposition fractions are plotted as functions of diffusion-equivalent diameter.     

Measurements of the total and regional deposition of inhaled particles in the human respiratory tract

The total and regional deposition of monodisperse aerosols in the human respiratory tract has been measured in 12 healthy subjects breathing through the mouth. Radioactively labelled polystyrene particles in the aerodynamic diameter range 3.5–10.0 μm were employed. The total deposition results are similar to those reported by Stahlhofen et al. (1980), showing only a slight progressive increase with particle size, from a mean fraction of 0.79 of the inhaled aerosol at 3.5 μm, to 0.88 for 10 μm particles. The extrathoracic airways show a very marked deposition at all sizes, predominantly in the throat. The throat values rise rapidly from a mean of 0.09 at 3.5 μm to 0.36 at 10 μm particle diameter. Two intrathoracic fractions were also obtained by the widely accepted method of measuring the relative amounts of activity cleared from the thorax as a function of time. Alveolar deposition was apparently still some 0.06 of the inhaled aerosol at 10 μm particle diameter. Tracheo-bronchial deposition showed little change at any particle size except at 3.5 μm, when it was 0.24 of the inhaled aerosol.     

Influence of pressure, temperature and surface area/volume ratio on the texture of pyrolytic carbon deposited from methane

The kinetics of carbon deposition from methane were studied over broad ranges of pressures, temperatures and reciprocal surface area/volume ratios. Based on these results, it was possible to distinguish between a growth and a nucleation mechanism of carbon deposition and to select conditions for the preparation of well-defined samples for texture analysis by transmission electron microscopy and selected area electron diffraction. Maximal texture degrees were obtained at medium or high values of the above parameters, but never at low values, at which carbon formation is based on the growth mechanism and dominated by small linear hydrocarbons. High-textured carbon resulting from the growth mechanism is concluded to be formed from a gas phase with an optimum ratio of aromatic to small linear hydrocarbons, which supports the earlier proposed particle-filler model of carbon formation. High-textured carbon may also be formed from a gas phase dominated by polycyclic aromatic hydrocarbons (nucleation mechanism) provided that the residence time is sufficiently long that fully condensed, planar polycyclic aromatic hydrocarbons can be formed in the gas phase.     

Analysis and evaluation of permeability techniques for characterizing fine particles Part II. Measurement of specific surface area

The performance of both steady-state and transient permeameters has been evaluated. A number of standard powders was chosen and their surface areas determined by gas adsorption techniques for comparison with surface areas obtained using permeameters. The powders were chosen to cover a wide range o density (0.92 – 18.7 g/cm³) and surface area (0.06 – 350 m²/g).The effect of particle shape, i.e. needles, spherical particles, flakes and irregularly shaped particles on surface area determined by permeametry has also been studied. A linear relationship between BET surface area and that obtained by using a simple U-tube transient flow permeameter has been obtained over a wide range of particle size and macroporosity.The Fisher Subsieve Sizer was chosen as a typical example of a steady-state permeameter, and a number of shortcomings in this instrument have been found. A simple steady-state permeameter was constructed to evaluate the theoretical model as developed in Part I for atmospheric pressure permeametry, and the model has been found to give good values of external surface areas for powders having an average particle size greater than 2 μm. The effect of slip flow for particles less than 1 μm in diameter has been established for atmospheric pressure permeametry.This paper also presents measurements of specific surface area determined by using a more recent permeameter, namely the Permaran. This instrument performed within a reproducibility of ±7% and produced data in agreement with that taken on similar devices and also with the theoretical analysis presented in Part I.The performance of a Knudsen-flow permeameter has been evaluated, and the instrument has been found to give accurate values of external surface area of fine as well as coarse powders.     

Mathematical models of particle deposition in the human respiratory tract

Several mathematical formalisms have been proposed to calculate particle transport onto airway surfaces: the temporally and spatially discrete Findeisen formalism; the temporally discrete and spatially continuous Altshuler formalism; and the temporally and spatially continuous Taulbee-Yu formalism; they are termed primary deposition models. Models adopting these formalisms are termed secondary deposition models. This review concentrates on the discussion of the general concepts of primary models and their numerical verification and on characteristics of secondary models. Current deposition models predict particle deposition in close agreement with current experimental data.     

Deposition of fractal-like soot aggregates in the human respiratory tract

Deposition of diesel exhaust particles in the human respiratory tract is calculated in terms of the equivalent mobility diameter while accounting for the aggregate's number of primary spherules, N_p, and its mass mobility fractal dimension. The size and shape of the soot particles studied correspond to emissions from diesel engines under different loading conditions. The aggregate's morphology, characterized by the aggregate mass mobility fractal dimension D_fm, is shown to significantly affect its age- and ventilation-specific deposition patterns in the human respiratory tract and hence, the exposure experienced by the receptor. Reporting respiratory tract deposition of diesel soot solely in terms of the aggregate mobility diameter, which lumps together size and shape, precludes a close look at deposition patterns of real particles and does not provide a complete picture for exposure inference.For sedentary adults, soot aggregates tend to deposit in the pulmonary region, with large open aggregates depositing to a greater extent than large compact aggregates. In most cases, and for open structured aggregates in particular, the aggregate deposition exceeds the deposition of their equivalent volume spheres. Whereas adults experience higher total respiratory tract soot deposition, infants are more susceptible to proximal deposition of open aggregates (D_fm<2.2). For an adult performing intense activity both the tracheobronchial and the alveolar deposition fractions are smaller than at rest, whereas extrathoracic deposition increases during intense activity. Alveolar deposition of soot aggregates is evident mainly during rest and is more pronounced for small aggregates (N_p<50).     

Variation of the specific surface area and porosity of anhydrous zinc oxalate with water vapour pressure

Specific surface areas and pore structure studies were carried out on two sets of samples of anhydrous zinc oxalate prepared from the dihydrate by heating at 130 and 180°C in various atmospheres of differing water vapour pressure. The two sets of samples were freshly prepared and aged samples. The variation of specific surface areas with water vapour pressure was found to behave in accordance with the Smith-Topley effect, with a minimum S_BET value located at 3.0 mmHg of water vapour. Analysis of the nitrogen adsorption isotherms by the t-method revealed the existence of both micropores and mesopores in the freshly prepared samples heated both at 130 and 180°C in 8.0 mmHg water vapour, and also in the aged samples prepared at 130°C in vacuo, and at 180°C in 8.0 mmHg water vapour. The rest of the samples possess only wide pores. Complete pore structure analysis for both micro- and mesopores was carried out for all samples investigated, and an attempt was made to correlate the factors affecting the development of surface area and pore structure, both in the presence and absence of water vapour, with those affecting the dehydration rate, and which occasionally lead to the Smith-Topley effect.     

Variation of the specific surface area and porosity of anhydrous zinc oxalate with water vapour pressure

Specific surface areas and pore structure studies were carried out on two sets of samples of anhydrous zinc oxalate prepared from the dihydrate by heating at 130 and 180°C in various atmospheres of differing water vapour pressure. The two sets of samples were freshly prepared and aged samples. The variation of specific surface areas with water vapour pressure was found to behave in accordance with the Smith-Topley effect, with a minimum S_BET value located at 3.0 mmHg of water vapour. Analysis of the nitrogen adsorption isotherms by the t-method revealed the existence of both micropores and mesopores in the freshly prepared samples heated both at 130 and 180°C in 8.0 mmHg water vapour, and also in the aged samples prepared at 130°C in vacuo, and at 180°C in 8.0 mmHg water vapour. The rest of the samples possess only wide pores. Complete pore structure analysis for both micro- and mesopores was carried out for all samples investigated, and an attempt was made to correlate the factors affecting the development of surface area and pore structure, both in the presence and absence of water vapour, with those affecting the dehydration rate, and which occasionally lead to the Smith-Topley effect.     

Dendritic deposition of uncharged aerosol particles on an uncharged fiber in the presence of an electrical field

A Monte Carlo simulation method based on particle trajectory calculations is used to study the effect of a uniform electrical field on the dendritic deposition of uncharged dielectric aerosol particles on uncharged dielectric fibres. The system parameters are chosen so that the main mechanisms of deposition are interception and electrical attraction. The main electrical force on an oncoming particle is that exerted by the polarized fiber and dendrites. It is found that simple superposition of the electrical fields of the polarized fibre and of the individual deposited particles gives an approximation to the actual field that is adequate for practical purposes. Based on such superposition, particle trajectories are calculated and the dendritic deposition phenomenon is studied. The effects of the electrical field are found to be very important and to increase with increasing field strength. In general, the electrical field increases the number of dendrites per unit length of fibre, and produces dendrites which are long, slender and tend to follow the force lines of the electrical field. The enhancement of the overall rate of deposition is also drastic and increases with increasing electrical field strength.     

Cake properties of nanocolloid evaluated by variable pressure filtration associated with reduction in cake surface area

A potential method has been developed for evaluating simultaneously both the average specific resistance and average porosity of the filter cake formed in unstirred dead‐end ultrafiltration of nanocolloids such as bovine serum albumin solution and silica sol. The method consists of variable pressure filtration followed by constant pressure filtration. The relation between the average specific cake resistance and the pressure drop across the cake was determined from the evolution of the filtration rate with time in the course of the variable pressure filtration period, based on the compressible cake filtration model. The average porosity was evaluated from the significant flux decline caused by a sudden reduction in the cake surface area in the middle of the constant pressure filtration period. The pressure dependences of both the average specific cake resistance and average cake porosity were obtained from only two runs which differed from each other in the pressure profiles. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3869–3877, 2014     

The hail impactor shape with an ice impact response of the laminated composites reinforced with different nanomaterials: an experimental approach

Iranian Polymer Journal - This study presents the response of twill glass fiber-epoxy laminates enhanced with different nanomaterials (0.5 wt%) subjected to high-velocity ice impact. The mechanical...     

Dynamic simulation of pressure swing adsorption system with the electrical network

With the electrical network model and object-oriented programming technique, a pressure swing adsorption (PSA) system may be decomposed to four objects: adsorbent column, tank, pressure source, and pipeline. Various flowsheets and operating patterns of PSA may be constructed with different combinations of objects and their topology. The objects are represented by class inheritance and encapsulation. The classes encapsulate the methods of setting up and solving the state equations according to the topological constraints and elemental constraints of resistor, capacitor, inductor and voltage and current sources. A PSA flowsheet may be represented with a heterogeneous list that creates the instances of the classes. The state equations are solved numerically on the basis of the polymorphic mechanism via virtual member functions in C++. A four-bed PSA process, consisting of four adsorbent columns, eight tanks, two constant pressure sources, four variable pressure sources and 30 pipelines, are simulated with the electrical network model. The simulated results agree well with the experimental data, and only 7-20 outer cyclic iterations are required to reach the cyclic steady state. The effect of the dead volume and fluid resistances in pipelines on operating results is examined. Optimal searching for the valve coefficients and operating time can suggest the corresponding suitable values to increase the experimental recovery.     

Numerical simulation of motion of rigid spherical particles in a rotating tumbler with an inner wavelike surface

The present work is a numerical simulation of motion of rigid spherical particles within a 2-D tumbler with an inner wavelike surface. The rotation of the tumbler is simulated as a traveling sine wave around a circle. The discrete element method (DEM, a hard sphere approach) is used. The particle-wall interactions are taken into account in a changed numerical approach of hard sphere model. The effects of two basic factors of the rotating velocity (phase velocity) and the wave numbers are separately investigated. A simple but useful method for cluster identification is provided and used. The energy-based analysis of particle clusters and the motion pattern study indicate the existence of a pulsed variation in the kinetic energy of the clusters at low wave numbers and a cyclic bulk motion of the clusters at high wave numbers. The necessary conditions for the pulsed variation of motion of particle clusters at low wave number are analyzed and a mode for industrial application, e.g. coal grinding process in power plant, is demonstrated.     

Size distribution and sites of origin of droplets expelled from the human respiratory tract during expiratory activities

A new expiratory droplet investigation system (EDIS) was used to conduct the most comprehensive program of study to date, of the dilution corrected droplet size distributions produced during different respiratory activities.Distinct physiological processes were responsible for specific size distribution modes. The majority of particles for all activities were produced in one or more modes, with diameters below 0.8 μm at average concentrations up to 0.75 cm^?3. These particles occurred at varying concentrations, during all respiratory activities, including normal breathing. A second mode at 1.8 μm was produced during all activities, but at lower concentrations of up to 0.14 cm^?3.Speech produced additional particles in modes near 3.5 and 5 μm. These two modes became most pronounced during sustained vocalization, producing average concentrations of 0.04 and 0.16 cm^?3, respectively, suggesting that the aerosolization of secretions lubricating the vocal chords is a major source of droplets in terms of number.For the entire size range examined of 0.3–20 μm, average particle number concentrations produced during exhalation ranged from 0.1 cm^?3 for breathing to 1.1 cm^?3 for sustained vocalization.Non-equilibrium droplet evaporation was not detectable for particles between 0.5 and 20 μm, implying that evaporation to the equilibrium droplet size occurred within 0.8 s.