Production Of Monodispersed Particles Research Articles

Synthesis of monodisperse, re-dispersable polymer particles by one-step high solid emulsion polymerization in the presence of reactive surfactant

In this study, monodispersed and re-dispersed poly (methyl methacrylate) (PMMA) particles were prepared by high solid content (50 wt%) macroemulsion polymerization using commercial macromonomer (Emulsogen APS 100) as a reactive surfactant (surfmer). Highly monodispersed, re-dispersed PMMA particles with sizes around 300 nm were obtained using this process. The effect of recipe composition including surfmer content, monomer/water ratio and electrolyte concentration on particle formation and growth were also investigated. Compared to classical macroemulsion polymerization theory, the formation of particles was found different. The number of formed particles firstly increased to a maximum value, then rapidly decreased to reach a constant value stabilized at around 1/5 of the maximum particle number. The particle coagulation theory was used to explain the process of particle formation and growth. The relationship between polymer particle size distribution and particle coagulation was also examined and the results were discussed. The proposed method would probably find applications in industrial production of monodisperse particles.

Reduction of Dust Emission by Monodisperse System Technology for Ammonium Nitrate Manufacturing

Prilling is a common process in the fertilizer industry, where the fertilizer melt is converted to droplets that fall, cool down and solidify in a countercurrent flow of air in a prilling tower. A vibratory granulator was used to investigate liquid jet breakup into droplets. The breakup of liquid jets subjected to a forced perturbation was investigated in the Rayleigh regime, where a mechanical vibration was applied in order to achieve the production of monodispersed particles. Images of the jet trajectory, breakup, and the formed drops were captured using a high-speed camera. A mathematical model for the liquid outflow conditions based on a transient two-dimensional Navier–Stokes equation was developed and solved analytically, and the correlations between the process parameters of the vibrator and the jet pressure that characterize their disintegration mode were identified. The theoretical predications obtained from the correlations showed a good agreement with the experimental results. Results of the experiments were used to specify the values of the process parameters of the vibration system, and to test them in the production environment in a mode of monodispersed jet disintegration. The vibration frequency was found to have a profound effect on the production of monodispersed particles. The results of experiments in a commercially-sized plant showed that the granulator design based on this study provided prills with a narrower size range compared to the conventional granulators, which resulted in a substantial reduction in dust emission.

A Microfluidic Platform to design crosslinked Hyaluronic Acid Nanoparticles (cHANPs) for enhanced MRI.

Recent advancements in imaging diagnostics have focused on the use of nanostructures that entrap Magnetic Resonance Imaging (MRI) Contrast Agents (CAs), without the need to chemically modify the clinically approved compounds. Nevertheless, the exploitation of microfluidic platforms for their controlled and continuous production is still missing. Here, a microfluidic platform is used to synthesize crosslinked Hyaluronic Acid NanoParticles (cHANPs) in which a clinically relevant MRI-CAs, gadolinium diethylenetriamine penta-acetic acid (Gd-DTPA), is entrapped. This microfluidic process facilitates a high degree of control over particle synthesis, enabling the production of monodisperse particles as small as 35 nm. Furthermore, the interference of Gd-DTPA during polymer precipitation is overcome by finely tuning process parameters and leveraging the use of hydrophilic-lipophilic balance (HLB) of surfactants and pH conditions. For both production strategies proposed to design Gd-loaded cHANPs, a boosting of the relaxation rate T1 is observed since a T1 of 1562 is achieved with a 10 μM of Gd-loaded cHANPs while a similar value is reached with 100 μM of the relevant clinical Gd-DTPA in solution. The advanced microfluidic platform to synthesize intravascularly-injectable and completely biocompatible hydrogel nanoparticles entrapping clinically approved CAs enables the implementation of straightforward and scalable strategies in diagnostics and therapy applications.

Pulsed back-and-forward cross-flow batch membrane emulsification with high productivity to obtain highly uniform and concentrate emulsions

Membrane emulsification of soybean oil in an aqueous solution of 2wt% Tween 80 was performed using pulsed back-and-forward flow. A tubular Shirasu porous glass (SPG) membrane with mean pore diameter of 3.1μm was used. Soybean oil was pressed through the membrane and the force that determines droplets detachment was exerted by the continuous phase tangentially agitated by inverting the flow direction back-and-forward within the membrane lumen. Alternatively, droplets were spontaneously detached from the pore opening in the absence of shear flow at the membrane surface.The main advantage of the pulsed back-and-forward cross-flow membrane emulsification is that it eliminates the shear stress outside of the membrane related to the recirculation of emulsion droplets along the pump and fitting circuit as it happens in conventional cross-flow membrane emulsification. Results obtained indicated that it was possible obtaining uniform emulsion droplets also when high concentration of dispersed phase was reached with high productivity comparing with the traditional cross-flow membrane operation. The method is suitable for the production of monodispersed particles containing bioactive molecule (that are shear sensitive) or viscous dispersed materials or large droplets.

Generalizing the polymerization conditions for the production of monodisperse polymeric particles via dispersion polymerization

In this study, the preparation of various methacrylic particles with monodisperse size via dispersion polymerization in polar media was discussed. The effect of various polymerization conditions such as polarity of the medium, monomer, stabilizer, and initiator concentration, polymerization temperature, and initiator type on the size and size distribution of these particles was evaluated. The experimental results showed that, with a decrease in the difference between medium solubility parameter (MSP) and polymer solubility parameter (PSP), stabilizer concentration and with an increase in monomer content size of the particles increased and size distribution of them became broader. The obtained results showed that the particle size and size distribution of various polymers were different functions of initiator concentration. It means that, for the production of monodisperse particles, specific amount of initiator is needed for each type of the polymers. Moreover, it was observed that the size and size distribution of the particles with higher polarity were more sensitive to changing the polarity of the medium, and the size distribution of the particles with lower glass transition temperature (T g) is more sensitive to changing the stabilizer concentration which is because of less stability of them. Furthermore, to our surprise, the obtained results showed that, in MSP-PSP of 18.5 MPa0.5, size and size distribution of all types of the particles became equivalent.

Particle drying and crystallization characteristics in a low velocity concurrent pilot scale spray drying tower

A low velocity spray tower was built in Monash which allows the production of mono-dispersed particles. As part of a larger project in controlling the functionality of the particles produced, the computational fluid dynamics technique (CFD) was used to gain more insights into the drying characteristics of the mono-dispersed droplets. Introduction of droplet and mass transfer did not significantly alter the flow field. Analysis revealed that the wet bulb region was significant in this tower. Varying the inlet air temperature from 100°C to 180°C resulted in contrasting drying history. These drying kinetics were then extended to assess the in-situ crystallization phenomenon. For this spray drying tower, it was found that lower inlet temperature condition favoured a higher degree of crystallinity.

Production of monodispersed particles by using effective size selection

In this article we report the results of two size selection methods that are based on interfacial interaction between nanosize particles, magnetite in this case, anionic surfactants, and nonpolar solvents. It is proposed that by selecting a suitable surfactant type and/or conditions to modify the particle–particle separation distance, only smaller particles can be stabilized against aggregation and settling making a size sensitive separation possible. Using this phenomenon, an effective size selection at the nanosize level has been achieved and the preliminary results are presented here. Depending on the conditions, stable suspensions of nearly monodispersed nanoparticles of magnetite (diameter less than 10 nm and standard deviation, σ, below 0.2) were obtained from polydispersed powders (less than 40 nm in diameter and σ around 0.6) synthesized from aqueous solutions at 25 °C. Magnetization measurements of the fractions confirmed the effectiveness of the developed size selection methods.

Theory of production of monodisperse particles by electrostatic spraying of liquids

Under electrostatic dispersion of liquid from the meniscus of a capillary tip when the liquid is supplied through the capillary, emitted droplets appear unstable with regard to their own charge and disintegrate, ejecting ∼ 100 siblings that are two orders of magnitude smaller. If the liquid is supplied under pressure, the voltages applied to the electrodes vary depending on the values of the pressure and the emitted droplets are stable with regard to both their own charge and the external electric field of the electrode system. Sizes, charges, and specific charges of the small droplets are calculated on the basis of the minimum energy dissipation principle. A qualitative model of synchronization of the droplet emission process with an ac electric field has been proposed.

Effect of wafer orientation on the particle deposition in subatmospheric pressures

The significance of gravity, electrostatic force, and turbulence on particle deposition on wafers in subatmospheric pressure chambers was investigated by conducting experiments with wafers placed in various orientations in an e-beam evaporator chamber used in the fab line at the Microelectronics Center of North Carolina (MCNC). These experiments carried out with naturally occurring particles generated by the operation of the equipment indicated that gravity usually dominanted deposition. However, particle contamination on wafers in the vertical and upside down orientations suggested that electrostatic forces and turbulence within the chamber during venting and pumpdown also contributed to wafer contamination. In order to study particle deposition characteristics with known particles at subatmospheric pressures, a new particle generating method using a modified vibrating orifice aerosol generator (VOAG) was developed for the production of monodisperse particles at low pressures with controllable charge and concentration.

Development and Use of a System for Routine Production of Monodisperse Particles of 238PuO2 and Evaluation of Gamma Emitting Labels

A system has been designed, constructed, tested and used for producing large quantities of monodisperse (rog < 1.2) submicrometer particles of 238PuO2 with density about 7.8 g/cm3 which are being used in inhalation experiments with dogs and rodents. The system consists of a series of five stainless steel glove boxes housing the aerosol generation system for producing polydisperse 238PuO2, an aerosol chamber and four Lovelace Aerosol Particle Separator (LAPS) units to separate the polydisperse PuO2 into monodisperse fractions and collect them. The collected monodisperse particles of PuO2 are subsequently suspended in water containing a suitable particle stabilizing agent and nebulized to provide monodisperse respirable aerosols of 238PuO2 particles. The use of 51Cr and 169Yb as gamma-emitting labels for 238PuO2 has been studied. Much 51Cr left the 238PuO2 particles under the 1150°C heat treatment so that neither uniform nor adequate labeling was achieved. The nuclide 169Yb, however, was both a uniform and relatively stable label for 238PuO2 aerosols although ytterbium dissolution was somewhat higher than for the plutonium.

On the production of monodisperse particles with a spinning disc

An apparatus for the production of monodisperse particles, based on the spinning disc principle, has been constructed. It has been tested in production of polystyrene particles and it proved to be possible to make these with a standard deviation of 4 per cent in dia. The drop formation process at the edge of the disc has been photographed with a ruby laser technique. From the pictures, the formation of drops, satellite drops and double drops is discussed.