Μm Polystyrene Latex Particles Research Articles

Aqueous particle generation with a 3D printed nebulizer

Abstract. In this study, we describe the design and testing of a high-output-stability, constant-liquid-feed nebulizer using the Venturi principle to generate liquid particles from solutions. This atomizer, the PRinted drOpleT Generator (PROTeGE), was manufactured using stereolithography (SLA) printing. Different concentrations of ammonium sulfate solutions were used to characterize the size and number concentration of the generated particles. A comparison of a 3D printed 0.5 mm orifice against a commercially available 0.5 mm brass orifice using the same ammonium sulfate solution was also performed. The particle number concentration generated with the printed orifice was higher, by ∼×2, than the particle number concentration generated with the brass orifice. PROTeGE is also capable of dispersing polystyrene latex (PSL) spheres for calibration purposes. The particle number concentrations obtained in this study ranged from ∼ 10 000 cm−3 for 0.75 µm to ∼ 100 cm−3 for 5.0 µm PSL particles with a dependence on the concentration of the dispersed solution. For the different concentrated ammonium sulfate solutions particle number concentrations from ∼ 14 000 cm−3 for 0.1 g L−1 to 7600 cm−3 for 5.0 g L−1 were measured. An additional measurement with a scanning electrical mobility system (SEMS) was performed for the 0.6 g L−1 solution to measure particles in the size range of 10 to 1000 nm. The generated particle number size distributions (PNSDs) showed a maximum at 50 nm with particle number concentrations of ∼ 40 000 cm−3. PROTeGE is easy to manufacture and operate, low in maintenance, and cost-effective for laboratory and field generation of particles from aqueous media in a size range of 10 to 5000 nm.

Design and development of an Electrostatic Screen Battery for Emission Control (ESBEC)

Current diesel particulate filters (DPFs) can effectively capture the exhaust particles, but they add to engine backpressure and accumulate particles during their operation, which results in the need to regenerate the DPFs by burning off the collected particles periodically. This regeneration results in aerosol emissions, especially in the 10–30 nm size range and contributes to ultrafine particle pollution. In this research, we designed and developed a prototype of a novel diesel exhaust control device: the Electrostatic Screen Battery for Emissions Control (ESBEC). The device features high particle collection efficiency without adding to the exhaust backpressure and without the need for thermal regeneration of the collected particles. The ESBEC consists of a series of metal mesh screens coated with a superhydrophobic substance and an integrated carbon fiber ionizer to charge the incoming particles. Multiple pairs of screens (e.g., 5 pairs) are arranged in a battery, in which one screen of each pair is supplied with high voltage, and the other is grounded, producing electrostatic field produced across the screens. The application of a superhydrophobic coating onto the screens allows easy removal of the collected particles using liquid without the need for thermal regeneration. The current prototypes of the device were tested with fluorescent polystyrene latex (PSL) particles of 0.2 and 1.2µm in size and at 25 and 105L/min sampling flow rates. The average collection efficiency was ~87% for 0.2µm and ~95% for 1.2µm PSL particles. In addition, the ESBEC was tested with actual diesel exhaust particles; here its performance was verified by visually inspecting deposition of particles on an after-filter with the device ON and OFF. In the next stages of this work, the ESBEC will be challenged with diesel exhaust at different mass concentrations and for different collection time periods.

Effective diffusivity of colloidal particle multilayers

We have studied, both theoretically and experimentally, the effective diffusivity of colloidal particle multilayers. We have synthesized the multilayers of 0.8μm polystyrene latex particles, according to the layer-by-layer technique. We have measured their limiting diffusion current, using cyclic voltammetry with rotating disk electrode, to determine the equivalent thickness of stagnant solution layer. Next, we have performed mass measurements of each film to determine its mean surface coverage. From these measurements, we have calculated thickness of the multilayers. We have also presented results of our numerical simulations of multilayer adsorption of hard monodisperse spheres, using the extended random sequential adsorption model. We have generated five multilayers mimicking those obtained experimentally. Then, we have analyzed their porosity, tortuosity, and effective diffusivity as functions of the distance from the adsorption surface. We have shown that variation in effective diffusivity within our multilayers has negligible effect on the concentration profile of species diffusing through the supported membranes. We have also compared the thickness of the multilayers, determined experimentally and theoretically. We have found a good agreement between the experiments and numerical simulations.

Continuous-flow size-based separation of microparticles by microchip electromagnetophoresis.

A novel microchip separation method for microparticles based on electromagnetophoresis was developed. In this method, a double Y-shape microchip with two inlets and two outlets was used for particle separation. Microparticles of two different sizes were suspended in an aqueous solution and introduced into the microchannel from one inlet with a stream of the aqueous solution without particles from another inlet by a hydrodynamic flow. Then, the particles with two different sizes were migrated orthogonal to the flow by elctromagnetophoresis and separated to different outlets based on the difference in their electromagnetophoric velocities, which depended on the size of particle. Using this method, at one outlet, 89% of 3 μm polystyrene latex particles were isolated from a mixture of 3 and 10 μm particles. By combining hydrodynamic focusing, both 3 and 10 μm particles were recovered at the different outlets with 100% purity and recovery, respectively. Even the separation of 3 and 6 μm particles was also achieved with about 98% recovery and purity. Moreover, yeast cells and polystyrene particles could be separated with high separation efficiency by this technique.

Performance Evaluation of Selected N95 Respirators and Surgical Masks When Challenged with Aerosolized Endospores and Inert Particles

The objective of this study was to assess how the relative efficiency of N95 respirators and surgical masks might vary with different challenge aerosols, utilizing a standardized manikin head form as a surrogate to human participation. A Collision nebulizer aerosolized B. anthracis Sterne strain endospores and polystyrene latex (PSL) particles to evaluate 11 models of N95 respirators and surgical masks. An automated breathing simulator, calibrated to normal tidal volume and active breathing rate, mimicked human respiration. A manikin head form with N95 respirators or surgical masks, and manikin head form without N95 respirators or surgical masks were placed in the bioaerosol chamber. An AGI-30 sampler filled with phosphate buffered water was fitted behind the mouth of each manikin head form to collect endospore bioaerosol samples. PSL aerosols concentrations were quantified by an ARTI Hand Held Particle Counter. Geometric Mean (GM) relative efficiency of N95 respirators and surgical masks challenged with endospore bioaerosol ranged from 34–65%. In PSL aerosol experiments, GM relative efficiency ranged from 35–64% for 1.3 μm particles. GM filtration efficiency of all N95 and surgical N95 respirators filter media evaluated was ≥99% when challenged with particles ≥0.1 μm. GM filtration efficiency of surgical mask filter media ranged from 70–83% with particles ≥0.1 μm and 74–92% with 1.3 μm PSL particles. Relative efficiencies of N95 respirators and surgical masks challenged with aerosolized B. anthracis endospores and PSL were similar. Relative efficiency was similar between N95 respirators and surgical masks on a manikin head form despite clear differences in filtration efficiency. This study further highlights the importance of face seal leakage in the respiratory protection provided by N95 respirators, and demonstrates it on a human surrogate.

Primary standard for the number concentration of liquid-borne particles in the 10 to 20 µm diameter range

The national primary standard for the number concentration of liquid-borne particles in the 10 to 20 µm diameter range has been developed at the National Institute of Advanced Industrial Science and Technology (AIST), Japan. The standard consists of a total number counting type flow cytometer (T-FCM) and an electronic balance. The T-FCM is a commercial flow cytometer modified so that the total number of particles in an aqueous suspension sampled in a test tube can be counted, and the electronic balance is used to determine the mass of the suspension. This standard is intended to be used for calibrating commercial standard suspensions of monodisperse polystyrene latex (PSL) particles. The measurand in the calibration is the mass-based number concentration (the particle number in a unit mass of a suspension), and the calibration capability covers the concentration range from 5 × 102 to 2 × 106 particles g−1. When the concentration of the suspension is higher than 2 × 103 particles g−1, the suspension is first diluted to about 1 × 103 particles g−1 to suppress the coincidence loss in particle counting by the T-FCM. The validity of the calibration with the T-FCM was examined by comparison with an independent method in which a scanning electron microscope (SEM) was used to determine the number concentration of particles deposited on a silicon wafer. For a suspension of 10 µm PSL particles with a concentration of approximately 1 × 106 particles g−1, the concentration values determined by the T-FCM and SEM methods were 1.042 × 106 and 1.035 × 106 particles g−1, respectively: The difference was less than 0.7%. The relative expanded uncertainty of the measurement by the T-FCM method with the coverage factor k = 2 was 4.4%.

Assembly of hollow spheres by templated liquid phase deposition following the principles of biomineralisation

Hollow spheres with a hierarchically ordered wall structure are obtained by mineralisation of TiO2 on spherical assemblies of 2 µm polystyrene latex particles in a process mimicking all four stages of natural biomineralisation.

Force Measurements between Weakly Attractive Polystyrene Particles

The forces between two 4.5 μm polystyrene latex particles in an aqueous suspension have been measured using “differential electrophoresis”. The experiments were done in the presence of electrolyte (KCl), surfactant (SDS), silica nanoparticles, and polyelectrolyte (sodium polystyrene sulfonate, NaPSS). When the solution contained only KCl, colloidal doublets formed, and the forces between the particles were much larger than classical predictions; the particles in fact appeared to be adhered together irreversibly. In the presence of SDS−KCl solutions, similar results were obtained. Next, solutions with KCl and silica nanoparticles were made, and doublets again formed. While about 40% of the doublets showed piconewton-size attractive forces, about 60% again appeared to be adhered together irreversibly. Finally, NaPSS−KCl solutions were made; in this case, many colloidal doublets formed, and about 90% showed attractive forces of O(1 pN). Although the mechanism for this consistent but weak aggregation in the p...

Measurements of Charge Nonuniformity on Polystyrene Latex Particles

The experimental technique of rotational electrophoresis, similar in principle to standard translational electrophoresis, has been developed to quantify the charge nonuniformity on Brownian colloidal particles. Experiments were conducted on doublets of 4.5 μm polystyrene latex particles under various solution conditions, finding variations in zeta potential on individual particle surfaces of 50−75% of the average zeta potentials. Significant charge nonuniformity was found for all systems studied, indicating that charge nonuniformity might be critical in many colloidal applications.

Cell Traction Forces on Soft Biomaterials. I. Microrheology of Type I Collagen Gels

A laser-trap microrheometry technique was used to determine the local shear moduli of Type I collagen gels. Embedded 2.1 μm polystyrene latex particles were displaced 10–100 nm using a near-infrared laser trap with a trap constant of 0.0001 N/m. The trap was oscillated transversely ±200 nm using a refractive glass plate mounted on a galvanometric scanner. The displacement of the microspheres was in phase with the movement of the laser trap at frequencies less than 1 rad/s, indicating that at least locally, the gels behaved as elastic media. The local shear modulus was measured at various positions throughout the gel, and, for gels at 2.3 mg/mL and 37°C, values ranged from G = 3 to 80 Pa. The average shear modulus G = 55 Pa, which compares well with measurements from parallel plate rheometry.

The Effect of Time and Humidity on Particle Adhesion and Removal

Time and humidity greatly influence particle adhesion and removal in many particlesubstrate systems. The effect of time (aging) and humidity on the adhesion and removal of 22 μm PSL (Polystyrene Latex) particles on polished silicon wafers is investigated. The results show that the effect of time on the adhesion and removal of the 22 μm PSL particles on silicon substrates in high humidity environment is very significant. The removal efficiency of PSL particles significantly decreased after the samples were aged for more than one day in high humidity environment. The combined effect of the van der Waals force and the capillary force tend to accelerate the adhesion-induced deformation process. When capillary force occurs at the particle substrate interface, the removal efficiency decreases quickly by more than 50% within 24 hours. Without the capillary force, the adhesion-induced deformation is negligible within the first 24 hours.

A direct method for studying particle deposition onto solid surfaces

An experimental technique has been developed to study the deposition of colloidal particles under well controlled hydrodynamic conditions. The deposition process is observed under a microscope and recorded on video tape for further analysis. Fluid flow conditions in the experimental set-up were determined by numerical solution of the Navier-Stokes equations. Mass transfer equations were solved numerically (taking into account hydrodynamic, gravitational, electric double layer, and dispersion forces) for the stagnation point region. Also, some analytical solutions are presented. Deposition has been studied of 0.5μm polystyrene latex particles on cover glass slides used as collectors. From an analysis of the shape of the coating density vs. time curves and independently from the distribution of the particles on collector surfaces, it was found that one particle is able to block an area of about 20 to 30 times its geometrical cross-section. The initial flux of particles to the collector for a given salt concentration was found to depend strongly on the method of cleaning the collector surface. In general the flux and the escape of particles to and from the collector surface are sensitive to the interaction energy at small separations. The direct method of observing particle deposition and detachment could lead to important insights into the nature of particle-wall interactions at near contact.