Generation of Submicron Arizona Test Dust Aerosol: Chemical and Hygroscopic Properties

This article describes a submicron dust aerosol generation system based on a commercially available dust disperser intended for use in laboratory studies of heterogeneous gas–aerosol interactions. Mineral dust particles are resuspended from Arizona Test Dust (ATD) powder as a case study. The system output in terms of number and surface area is adjustable and stable enough for aerosol flow reactor studies. Particles produced are in the 30–1000 nm size range with a lognormal shape of the number size distribution. The particles are characterized with respect to morphology, electrical properties, hygroscopic properties, and chemical composition. Submicron particle elemental composition is found to be similar for the particle surface and bulk as revealed by X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical emission spectroscopy (ICP-OES), respectively. A significant difference in chemical composition is found between the submicron aerosol and the ATD bulk powder from which it was generated. The anionic composition of the water-soluble fraction of this dust sample is dominated by sulfate. Resuspended dust particles show, as expected, nonhygroscopic behavior in a humid environment. Small hygroscopic growth of about 1% (relative change in mobility diameter) was observed for 100 nm particles when the relative humidity (RH) was changed from 12 to 94%. Particles larger than 100–200 nm shrank about 1% once exposed to RH > 90%. This was interpreted as a restructuring of the larger agglomerates of dust to particles of smaller mobility diameter, under the influence of water vapor.     

Size Distribution of Health-Relevant Trace Elements in Airborne Particulate Matter During a Severe Winter Stagnation Event: Implications for Epidemiology and Inhalation Exposure Studies

Size distributions for As, Cd, Bi, Br, Fe, Mn, S, Sb, Tl, K, V, Rb, elemental carbon (EC), organic carbon (OC), sulfate (SO ^2? ₄ ), chloride (Cl^?), and nitrate (NO^? ₃ ) were measured at Bakersfield and Modesto CA between 12/15/2000–01/07/2001. S and V size distributions were highly correlated with little diurnal variation suggesting that, during stagnant winter conditions, inhalation exposure and epidemiological studies can choose exposure/analysis times of several days during which population exposure will be relatively uniform. In contrast, the size distribution and temporal patterns of Fe are highly variable requiring more frequent measurements and shorter health analysis periods to adequately characterize exposure concentrations. K and Rb (tracers for wood smoke) exhibited nearly identical diurnal size distribution shifts (R ²  > 0.99) with smaller particles emitted at night and larger aged particles evident during the day. This pattern suggests that the health effects of fresh wood smoke could be studied through nighttime inhalation exposure experiments and aged wood smoke could be evaluated through daytime experiments. All of the components’ size distributions were consistent with production by combustion sources and/or secondary chemistry. Future inhalation exposure studies should use a combustion source to generate these particles. Lung deposition calculations predict that 32 ± 11% of PM deposition occurs in the pulmonary region, 61 ± 23% occurs in the respiratory region, and 6 ± 2% occurs in the tracheo-bronchial region for all components. Deposition patterns were highly correlated with PM _1.8 concentrations suggesting that exposure estimates can be developed with bulk filter samples during the current episode.     

An In Situ Method for Sizing Insoluble Residues in Precipitation and Other Aqueous Samples

Particles are frequently incorporated into clouds or precipitation, influencing climate by acting as cloud condensation or ice nuclei, taking up coatings during cloud processing, and removing species through wet deposition. Many of these particles, particularly ice nuclei, can remain suspended within cloud droplets/crystals as insoluble residues. While previous studies have measured the soluble or bulk mass of species within clouds and precipitation, no studies to date have determined the number concentration and size distribution of insoluble residues in precipitation or cloud water using in situ methods. Herein, for the first time we demonstrate that nanoparticle tracking analysis (NTA) is a powerful in situ method for determining the total number concentration, number size distribution, and surface area distribution of insoluble residues in precipitation, both of rain and melted snow. The method uses 500 μL or less of liquid sample and does not require sample modification. Number concentrations for the insoluble residues in aqueous precipitation samples ranged from 2.0–3.0 (±0.3)?×?10⁸ particles cm^?3, while surface area ranged from 1.8 (±0.7)–3.2 (±1.0) × 10⁷ μm² cm^?3. Number size distributions peaked between 133 and 150 nm, with both single and multi-modal character, while surface area distributions peaked between 173 and 270 nm. Comparison with electron microscopy of particles up to 10 μm show that, by number, >97% residues are <1 μm in diameter, the upper limit of the NTA. The range of concentration and distribution properties indicates that insoluble residue properties vary with ambient aerosol concentrations, cloud microphysics, and meteorological dynamics. NTA has great potential for studying the role that insoluble residues play in critical atmospheric processes.

Copyright 2015 American Association for Aerosol Research     

Preparation of a new superhydrophobic nanofiber film by electrospinning polystyrene mixed with ester modified silicone oil

A new superhydrophobic nanofiber membrane with certain mechanical strength was prepared by electrospinning the polystyrene (PS) with ester modified silicone oil (EMSO). To increase the roughness and tensile strength, the EMSO with low energy as hydrophobic macromolecular substance was added into PS precursor solution. Then during the process of electrospinning, some of the ester modified silicone oil was distribution on the surface of substrate (PS) fiber films to generate double structure which leaded to the superhydrophobicity. We probed into the relationship between the surface wettability, morphologies, mechanical property, and the mass ratios of ester modified silicone oil /PS, and with the increasing of EMSO, the water CA value increased from 135 ± 0.5° to 152 ± 0.2°and the tensile strength grown from 0.23 MPa to 0.92 MPa. The film shows a network structure consisting of numerous randomly oriented fibers, the diameters of which changed from 0.5 μm to 2.0 μm belong to relatively big diameter fibers, which has great significance to the research of superhydrophobic membrane with big diameter fibers and also this method is easy, convenient and environment friendly. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40718.     

Mechanical properties of individual fiber segments of electrospun lignocellulose‐reinforced poly(vinyl alcohol)

The influence of lignocellulosic nanofibers (LCNF) additive on the inherent mechanical properties of submicron electrospun poly(vinyl alcohol) (PVA) fibers is reported. LCNF with a diameter of 25 ± 15 nm and a length of 220 ± 90 nm obtained from hemp shives were dispersed in aqueous PVA solutions to produce homogeneous nanocomposite fibers with 0, 5, and 10 w/w % LCNF loads in solid PVA. Tensile tests on mats show that LCNF additive causes up to sevenfold increase in stiffness and significant decrease in elongation at yield. AFM‐based 3‐point bending tests on single LCNF‐doped fibers reveal up to 11.4 GPa Young's modulus in the diameter range of 300 to 500 nm, indicating a 2.4 times increase compared to neat PVA fibers. Mechanical properties of both neat and LCNF‐doped PVA fibers are found to be strongly size‐dependent at lower fiber diameters, with Young's modulus values exceeding 100 GPa at below 100 nm diameters. The results can be explained by extensive restructuration of hydrogen bonding network due to the LCNF additive. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44361.     

High Precision Density Measurements of Single Particles: The Density of Metastable Phases

We describe a system designed to measure the size, composition, and density of individual spherical particles in real time. It uses a Differential Mobility Analyzer (DMA) to select a monodisperse particle population and the single particle mass spectrometer to measure individual particle aerodynamic diameter. Together the mobility and aerodynamic diameters yield particle density. The mass spectrometer aerodynamic sizing resolution d _{ν a} /Δ d _{ν a} is ～ 50 and > 100 for 200 nm and 800 nm particles respectively and together with the DMA the overall system resolution is 20. We demonstrate that the line shape of the aerodynamic size distribution can be used to identify asphericity. We present results from two operational schemes: one suitable for most applications, yielding particle density with a precision of ± 2.5%, and a high precision variant, that uses an internal calibrant to remove any of the systematic errors and significantly improves the measurement quality. The high precision scheme is most suitable for laboratory studies, making it possible to follow slight changes in particle density. An application of the system to measure the density of hygroscopic particles in deep metastable phases near zero relative humidity is presented. The density data presented here are consistent with conclusions reached in a number of other studies, namely, that some particle systems, once deliquesced, persist as droplets down to near zero relative humidity.     

Mass Absorption Cross-Section of Ambient Black Carbon Aerosol in Relation to Chemical Age

Three differing techniques were used to measure ambient black carbon (BC) aerosols in downtown Toronto through 20 December 2006 to 23 January 2007. These techniques were thermal analysis, as performed by a Sunset Labs OCEC Analyzer (OCEC); light attenuation, as performed by an Aethalometer (AE); and photoacoustic analysis, as performed by a Photoacoustic Instrument (PA). These measurements of ambient PM _2.5 were used to investigate the effects of coating thickness on BC Mass Absorption Cross-section (MAC). MAC values were determined by comparing 880 nm and 370 nm AE measurements and PA measurements of b _abs (absorption coefficient, Mm^–1) to the OCEC measurements. Based on mass size distributions and supporting criteria, the PM _2.5 was classified as fresh, semi-aged, or aged. The average MAC values in these categories, based on the PA measurements, were 9.3 ± 1.8, 9.9 ± 2.0, and 9.3 ± 2.2 m ² /g (mean ± standard deviation), respectively, suggesting that any difference in coating thickness as a result of aging, on the time scale observed, did not produce a difference in MAC. In a second type of experiment, a thermodenuder was installed upstream of the AE, PA, and OCEC and samples were heated to 340°C in order to evaporate volatile and semi-volatile components within the coating. Based on the PA measurements, the average MAC values of these heated samples, for the fresh, semi-aged, and aged categories were 7.7 ± 2.2, 6.9 ± 2.2, and 9.1 ± 2.0 m ² /g, respectively. Similar differences in MAC were also observed by the AE. The decrease in MAC in the fresh and semi-aged samples was interpreted in terms of the degree of coating of the PM _2.5 . Results agreed well with predictions made by absorption amplification theory and had ramifications for calibration of filter-base attenuation and photoacoustic instruments.     

Production of bulk SiC parts by electrophoretic deposition from concentrated aqueous suspension

Abstract

This paper reports on electrophoretic deposition of SiC bulk parts from highly loaded aqueous suspensions of submicron and nanosized powders. The effects of suspensions parameters (ζ-potential, conductivity, solids content) and deposition parameters (voltage, current density, time) on quality of deposits were examined. It is presented that by using well defined suspension parameters high process stability is assured. For submicron powder, relatively high density was achieved, i.e. 60% TD (±2%), while for the nanosized SiC, the highest density was 42% TD (±2%). Mixing of powders did not result in density increase. Bulk >4 cm thick deposits were proved to have homogeneous density distribution, which is one of the advantages of electrophoretic deposition (EPD) process in comparison to other ceramic shape forming processes.     

Analysis of Aerosolized Particulates of Feedyards Located in the Southern High Plains of Texas

The objective of this study was to quantify, size, and examine the composition of particulates found in ambient aerosolized dust of four large feedyards in the Southern High Plains. Ambient air samples (concentration of dust) were collected upwind (background) and downwind of the feedyards. Aerosolized particulate samples were collected using high volume sequential reference ambient air samplers, PM ₁₀ and PM _2.5 , laser strategic aerosol monitors, cyclone air samplers, and biological cascade impactors. Weather parameters were monitored at each feedyard. The overall (main effects and estimable interactions) statistical (P < 0.0001) general linear model statement (GLM) for PM ₁₀ data showed more concentration of dust (μg/m ³ of air) downwind than upwind and more concentration of dust in the summer than in the winter. PM _2.5 concentrations of dust were comparable for 3 of 4 feedyards upwind and downwind, and PM _2.5 concentrations of dust were lower in the winter than in the summer. GLM (P < 0.0001) data for cascade impactor (all aerobic bacteria, Enterococcus spp, and fungi) mean respirable and non-respirable colony forming units (CFU) were 676 ± 74 CFU/m ³ , and 880 ± 119 CFU/m ³ , respectively. The PM ₁₀ geometric mean size (±GSD) of particles were analyzed in aerosols of the feedyards (range 1.782 ± 1.7 μm to 2.02 ± 1.74μm) and PM _2.5 geometric mean size particles were determined (range 0.66 ± 1.76 μm to 0.71 ± 1.71 μm). Three of 4 feedyards were non-compliant for the Environmental Protection Agency (EPA) concentration standard (150 μg/m ³ /24 h) for PM ₁₀ particles. This may be significant because excess dust may have a negative impact on respiratory disease.     

COMPARISON OF ION EXCHANGE AND DONNAN EQUILIBRIUM MODELS FOR THE PH-DEPENDENT ADSORPTION OF SODIUM AND CALCIUM IONS ONTO KRAFT WOOD PULP FIBERS

ABSTRACT

Management of nonprocess element (NPE) accumulation in pulp washing operations requires equilibrium models that predict the distribution of metals between the wash liquor and the pulp fibers. The overall goal of this study was to assess models for predicting the multi-component adsorption of hydrogen ions (H⁺), sodium ions (Na⁺), and calcium ions (Ca⁺²) onto bleached and unbleached kraft pulp fibers over a pH range of 2.7–11. As part of this study, binary equilibrium constants for hydrogen and metal ion exchange on carboxylate sites in bleached pulp (0.041 meq/g dry pulp) were measured at 25°C, with log K ^Na/Ca = ?1.604 ± 0.119, log K ^H/Ca = 0.633 ± 0.087, and intrinsic dissociation constant pK _io of 3.64 ± 0.46. Ion exchange and Donnan equilibrium models adequately predicted the multi-component equilibrium data for competitive adsorption of H⁺, Na⁺, and Ca⁺² onto bleached kraft wood pulp fibers. The ion exchange model was fully predictive, whereas the Donnan model required that the solution pH be known. At pH 2.7–6, the Donnan model predicted the adsorption of Na⁺ and Ca⁺² onto both bleached and unbleached wood pulp fibers better than the ion exchange model. The ion exchange model assumed that residual carboxylate in the pulp served as the only site for the competitive binding of hydrogen and metal ions. In contrast, the Donnan model assumed a non site-specific distribution of metal ions between charged fiber and external solution phases and a carboxylate site specific adsorption of hydrogen ions. Above pH 6, both models failed to predict that the calcium adsorption on unbleached brownstock pulp increased beyond the carboxylate site capacity, suggesting that other functional groups within the brownstock pulp with intrinsic dissociation constant values higher than carboxylate were providing additional binding sites for calcium.     

Simulation of Three-Dimensional Particle Deposition Patterns in Human Lungs and Comparison with Experimental SPECT Data

To further validate a stochastic particle deposition model, three-dimensional deposition patterns predicted by that model were compared with corresponding spatial particle deposition data obtained from SPECT measurements. In the in vivo inhalation experiments, two different polydisperse aerosols with mass median aerodynamic diameters of 1.6 μ m and 6.8 μ m were inhaled by 12 test subjects, using different nebulizers. Predicted and measured deposition data were compared on three different levels: (1) total lung deposition, (2) deposition per hemispherical shell, and (3) deposition per airway generation. First, experimental and theoretical total lung deposition data showed good agreement for both the fine (65 ± 9% vs. 55 ± 21%) and the coarse aerosols (55 ± 8% vs. 46 ± 4%). Second, predicted deposition per hemispherical shell also corresponded well with the experimental data, both exhibiting small deposition fractions in the inner shells and a roughly quadratic increase in the outer shells. Third, fair agreement was observed for the deposition fractions per airway generation, both experimental data and modelling predictions exhibiting relatively small deposition fractions in central bronchial airway generations, followed by a steep increase in the peripheral respiratory airways. While the overall agreement between measured SPECT data and computed deposition fractions demonstrates that SPECT data can indeed be used for model validation, the current spatial resolution of the SPECT method allows only a limited validation of model predictions at the single airway generation level.     

Polystyrene bioactive nanofibers using orange oil as an ecofriendly solvent

Solution blow spun polystyrene (PS) nanofibers were produced from 20 to 30 wt % PS solutions using toluene (industrial solvent) and orange oil (green solvent). The latter being composed of d -limonene (97.06%) as determined by gas chromatography–mass spectroscopy. The rheological behavior and volatility of the solvents and polymer solutions were correlated with fiber morphology, accessed by scanning electron microscopy. Thermal analysis was used to determine the thermal behavior of fibers. The antimicrobial activity of orange oil was tested for potential applications of the spun mats in active food packaging. Results showed that the nanofibers spun from orange oil solutions had average diameters of 306 ± 74 nm as opposed to 441 ± 110 nm for toluene. Moreover, when compared with fiber spun from toluene solutions, orange oil yielded more flexible fibers with slightly lower contact angles and better antimicrobial properties due to the presence of residual oil confirmed by Fourier-transform infrared spectroscopy. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47337.     

Fiber Bridging during Melt Electrowriting of Poly(ε-Caprolactone) and the Influence of Fiber Diameter and Wall Height

Melt electrowriting (MEW) is a direct-writing technology for small diameter fibers; however, due to electrostatic attraction, the technique is restricted in how close these microfibers can be positioned on the collector. Here, the minimum interfiber distance between parallel poly(ε-caprolactone) MEW microfibers is determined for different fiber diameters and number of layers on noncoated and star-shaped poly(ethylene oxide-stat-propylene oxide) (sP(EO-stat-PO))-coated glass coverslips. The effect of the fiber diameter, the number of fiber layers, and shape of turning loops affect precision and the minimum interfiber distance. Single fibers with diameter of 5, 10, and 15 µm have a minimum interfiber distance without fiber bridging of 33 ± 2.7, 54 ± 2.2, and 62 ± 2.7 µm, respectively. Increasing the number of layers to ten increases this minimum interfiber distance approximately twofold to 60 ± 3.5, 97 ± 4.5, and 102 ± 2.7 µm for the increasing fiber diameters. The sP(EO-stat-PO) slightly increases the minimum interfiber distance for the 15 µm diameter group only, with spacing for the 5 and 10 µm fibers unaffected by the coating. Identifying and determining the fabrication limits for MEW is highly instructional for users working and designing scaffolds with this technology.     

Hierarchical Self‐Assembly of Poly(Urethane)/Poly(Vinylidene Fluoride‐co‐Hexafluoropropylene) Blends into Highly Hydrophobic Electrospun Fibers with Reduced Protein Adsorption Profiles

Electrospinning of blend systems, combining two or more polymers, has gained increasing interest for the fabrication of fibers that combine properties of the individual polymers. Here, a versatile method to produce hydrophobic fibers composed of poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDFhfp) and polyurethane (PUR) is presented. PVDFhfp containing fibers are expected to reduce protein adsorption. In a one‐step process, blend solutions are electrospun into homogeneous nonwoven membranes with fiber diameters in the range of 0.6 ± 0.2 to 1.4 ± 0.7 µm. Surface fluorine concentrations measured by X‐ray photospectroscopy show an asymptotic dependency in function of the PVDFhfp to PUR ratio, reaching values close to pure PVDFhfp at a weight per weight ratio of 10% PVDFhfp to 90% PUR. This fluorine enrichment on the surface suggests a gradient structure along the fiber cross‐section. At increased surface fluorine concentration, the contact angle changes from 121 ± 3° (PUR) to 141 ± 4° (PUR/PVDFhfp). Furthermore, these highly hydrophobic fibers present significantly reduced fibrinogen or albumin adsorption compared to PUR membranes.     

Oxidative solution polymerization of aniline hydrochloride onto electrospun nanofibers mats of polylactic acid: Preparation method and characterization

In this work, we present the preparation of polylactic acid (PLLA)/polyaniline (PANI) conductive composite nanofibers mats. They are prepared by bulk oxidative solution polymerization of PANI onto electrospun non‐woven fibers mats of PLLA. The PANI ratio in the composite is about 70%w/w. Scanning electron microscopy (SEM) shows that PLLA nanofibers are randomly oriented, beads free with diameters of 186 ± 85 nm, The PLLA/PANI composite nanofibers diameter values are 518 ± 128 nm with a good adherence between PANI and PLLA nanofibers. DSC and XRD measurements reveal an amorphous structure of the electrospun PLLA fibers due to the rapid evaporization of the solvent. FTIR and UV–vis spectra reflect good mutual interactions between PANI and PLLA chains. The DC‐conductivities ( ) far better than other published ones for similar composites prepared by bulk oxidative solution polymerization of PANI onto other electrospun nanofiber mats or with electrospun nanofibers from a solution mixture of PLLA and PANI. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41618.     

Effect of polyaspartic acid-functionalized graphene oxide on the mechanical performance of polyimide-based composites

Graphene oxide (GO) can improve the mechanical property of polymer matrix greatly. However, its poor dispersibility may considerably lower reinforcing efficiency. To address this problem, the environment-friendly polyaspartic acid (PASP) was adopted to modify GO through two generally modified methods: hydrogen bond adsorption and chemical graft modification. Findings indicate that the covalent bond grafted PASP–GO exhibits better dispersibility than the product by noncovalent method (PASP/GO-noncovalent). For chemically grafted PASP–GO, the nearly spherical polymer nanoparticles are formed on the GO nanosheets through self-polymerization, and its size can be well manipulated by adjusting the dosage of PASP so as to yield PASP–GO-1/4, PASP–GO-1/2, and PASP–GO-1/1 (mass ratio: m_PASP/m_GO = 1/4, 1/2, and 1/1); the corresponding diameters of these polymer aggregates are 56.4 ± 7.1, 90.1 ± 12.6, and 151.2 ± 16.1 nm. They are further utilized to reinforce polyimide matrix. Compared with the PASP–GO-1/2 and PASP–GO-1/1, the smaller PASP–GO-1/4 has better strengthening effect, due to its high specific surface area and dense distribution. This desirable fabrication of GO-based nanofillers provides a new avenue on the development of polymer matrix with comprehensive performances. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47939.     

Optical properties of non-absorbing mineral dust components and mixtures

Mineral dust is the second largest emission by mass into the atmosphere. Aerosol particles affect the radiative forcing budget by directly scattering and absorbing light, acting as cloud condensation and ice nuclei, and by providing surfaces for heterogeneous chemistry. Factors that affect how the particles scatter and absorb light include their composition, shape, size, and concentration. In this study, we characterize the most common components of mineral dust, quartz, and aluminosilicate clay minerals. In addition, we apply our results from calcite, feldspars, quartz, and aluminosilicate clay minerals to model the optical properties of Arizona test dust (ATD). We use cavity ring-down spectroscopy to measure the extinction cross sections of size-selected particles, electron microscopy to characterize the size selection, and Mie theory as well as the discrete dipole approximation as models. For quartz, the extinction cross sections can be well modeled assuming the particles are spheroids or spheres. For clay minerals, even spheroids fail to model the extinction cross sections, potentially due to orientation effects and lift forces in our flow system. In addition, aluminosilicate clay minerals experience weak size selectivity in the differential mobility analyzer. For ATD, the extinction cross sections are best modeled by treating each component of the mixture separately in terms of shape and size distribution. Through the application to ATD, our study outlines the procedure that can be used to model the optical properties of complex airborne dust mixtures.

Copyright © 2016 American Association for Aerosol Research     

Polypropylene microfibers via solution electrospinning under ambient conditions

Uniform beadless fibers of chlorinated polypropylene (PP-Cl) are prepared by electrospinning of PP-Cl solutions in tetrahydrofuran at different concentrations, feed rates, applied voltages, and tip-to-collector distances (TCDs) under ambient conditions for the first time. Average fiber diameter and morphology of the electrospun PP-Cl fibers are determined by scanning electron microscopy. On the other hand, the wettability of the fibers is examined by water contact angle (WCA) measurements. Furthermore, thermal behavior of fibers is investigated by differential scanning calorimetry and thermogravimetric analyses, respectively. Obtained results show that the higher concentrations and feed rates of polymer solutions not only enhance the average diameter of the electrospun fibers ranging from 2.2 ± 0.5 to 2.8 ± 0.3 μm but improve the hydrophobicity of the fiber surfaces from 128° ± 1.1 to 141° ± 1.0 as well. On the other hand, when applied voltage is increased or TCD is decreased, diameters of achieved fibers are enhanced. It is suggested that PP-Cl is an useful material for solution electrospinning process at under ambient conditions, exhibiting great scientific merit and good industrial expectation in the potential PP applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48199.     

Experimental and Modeling Studies of the Stream-Wise Filter Vibration Effect on the Filtration Efficiency

The stream-wise vibration effect of a fibrous filter is studied experimentally and numerically for the purpose of evaluating filtration efficiency. The particle sizes range from 0.02 to 10 μ m and the face velocity ranges from 3 to 10 cm/s. The vibrational peak velocity also varied from 0 to 50 cm/s. The filtration efficiency for this wide size range is obtained by combining the individual test results for fine particles (0.02 to 0.5 μ m) and large particles (0.5 to 10.0 μ m). For the fine particle experiment, Arizona Road Dust (ARD) test particles are generated by an atomizer after an ultrasonic process and measured by a Scanning Mobility Particle Sizer (SMPS). For the large particle experiment, the test particles are generated by a fluidized bed and measured by an Aerodynamic Particle Sizer (APS). When the particles are generated by the atomizer after ultrasonicating, the majority of the particles are in nano scale without the agglomerates on the large particle surface, while particles generated by the fluidized bed are mostly in micro-scale because many nanoparticles are agglomerated on large particle surface. The filtration efficiency increases with the vibrational peak velocity in the impaction-dominant region (D _p > 0.1 μ m) and diffusion-dominant region (D _p < 0.1 μ m), due to the increased relative velocity between the particle and the filter fiber and the increased diffusion intensity from turbulence around the fiber, respectively. A model for the filter vibration effect is established with a modified Stokes number for the impaction-dominant region and an empirical analysis for the diffusion-dominant region.     

Self-assembled cones of aligned carbon nanofibers grown on wet-etched Cu foils

Hot-filament chemical vapour deposition (HF-CVD) was used to grow aligned carbon nanofibers (CNFs) directly on Cu foils. Fast wet-chemical etching procedures based on hydrogen peroxide (H₂O₂) were found to have a key role on the formation of selective active substrates for the growth process. Here, a comprehensive mechanism is presented. Additionally, it is shown that nano-sized protrusions ∼8 nm with round shape and high density ∼1.7 × 10³ μm⁻² were decisive for the growth of aligned hollow-herringbone CNFs following the base-growth model. CNFs with heights of ∼1 μm and diameters around ∼8 nm show narrow diameter size distribution with remarkable correlation to the protrusion size distribution. The fibers were organised in cone-shape configurations with a cone density of ∼22 μm⁻² and a cone angle of 90°. An activation energy for the CNF growth of E_act ∼ 0.90 ± 0.16 eV was extracted from the Arrhenius plot showing that the process kinetics is governed by C diffusion in bulk Cu.