Droplet Size Determination Research Articles

How Cold Is Cold Enough? Refrigeration of the Next-Generation Impactor to Prevent Aerosol Undersizing.

Background: Heat transfer from impactor to aqueous aerosols causes underestimation of droplet size due to evaporation. Hence, pharmacopeia suggests cooling the impactor to 5°C, which is well below aerosol temperature. In this study, we assessed the droplet size at four different impactor temperatures under controlled ambient conditions to compare the compendial 5°C method with our in-house method, where the impactor is cooled to aerosol temperature.Materials and Methods: A single nebulizer/compressor unit was used throughout. It produced an aerosol at 17°C when operated at 50% RH and 23°C RT ambient conditions. Thirty-six experiments were conducted with saline, 9 each at impactor temperatures of 5°C, 10°C, 17°C, and 23°C. NaCl stage deposition was determined by conductometry, mass on stages by weighing. Moreover, a simulation was carried out to track aerosol temperature when entering the impactor.Results: Measuring at 23°C yields a significantly smaller mass median aerodynamic diameter (MMAD) than at 5°C–17°C. Despite elevated water condensation in the impactor at 5°C and 10°C, there was no increase in MMAD compared with 17°C. Instead, droplet size determination at 5°C led to significantly smaller values than at 17°C, probably due to distorted volumetric impactor flow rates at different impactor temperatures. Reevaluation of data with flow rates adjusted for impactor temperature (14.1 L/min at 5°C vs. 15.0 L/min at 23°C) led to indistinguishable results at 5°C–17°C. A computational fluid dynamics (CFD) simulation confirmed rapid cooling of the incoming air within the inlet and stage 1 and, with it, the systematic droplet undersizing due to reduced volumetric airflow using a cooled impactor.Conclusions: As long as the impactor temperature is at or below aerosol temperature, no effects on droplet size can be observed. Measuring at aerosol temperature yields the same results as at 5°C, but prevents condensation. However, cooling the impactor well below ambient temperature can cause a systematic error in the volumetric flow rate through the impactor if not corrected accordingly.

Influence of fat crystallization in W/O emulsions on the water droplet size determination by NMR diffusometry

HypothesisIt is expected that low resolution (LR) NMR diffusometry enables (more) accurate water droplet size determination for solid-fat based water-in-oil (W/O) emulsions with (sub)-micron size water droplets in comparison to liquid-oil based W/O emulsions due to hindered extra-droplet water diffusion. ExperimentsW/O emulsions with a volume-weighed mean diameter of about 1 µm and a solid fat content (SFC) ranging from 0% to 74% were produced. The aqueous phase contained the ionic marker tetraphenylphosphonium chloride (TPPCl). The water droplet size was estimated using LR and high resolution (HR) NMR diffusometry. FindingsHR-NMR diffusometry showed that the diffusion behavior of water and TPPCl was different, indicating water diffusion beyond the droplet’s interfacial boundaries. From a certain SFC onwards, a slower echo decay was observed for the water molecules, thus decreasing the overestimation of the water droplet size in (sub)micron W/O emulsions. For those emulsions, the solid fat matrix is believed to hinder extra-droplet water diffusion, which is most likely to be related to the increased tortuosity of the diffusive path in the porous fat crystal network. Using LR-NMR, it can be verified whether the water echo attenuation is mono-exponential or bi-exponential by increasing the gradient pulse duration for the maximum gradient strength, which is more convenient for routine analysis compared to HR-NMR.

Determination of spray droplet size by wavelet analysis of interferometric images

The problem of size droplet determining by the Interferometric Particle Imaging (IPI) in a spray of an optically transparent liquid is considered. The measurements were carried out using the example of a fuel injector flame. A new method for analyzing the IPI image of a droplet using a continuous wavelet transform is proposed. The spatial distribution of wavelet coefficients is used to introduce an integral measure similar to the spectral density of the signal. As a reliable estimate of the droplet size, we considered the results by the Glare Point Technique (GPT), which were applied simultaneously. A comparative analysis of the sizes obtained using GPT and IPI showed that the application of the wavelet transform to IPI images, in comparison with the Fourier method, significantly reduces the frequency of occurrence of a systematic error in determining the size, which is most specific for large droplets. It was found that the false maxima in the Fourier spectrum causing these errors are due to the appearance of distortions at the boundary of the interferometric image of the droplet. The wavelet transform allows one to separate these distortions from the main maximum in the vicinity of the droplet center.

Enhanced oral bioavailability of Bisdemethoxycurcumin-loaded self-microemulsifying drug delivery system: Formulation design, in vitro and in vivo evaluation.

In this study, we sought to overcome the poor solubility and bioavailability of bismethoxycurcumin (BDMC) by fabricating a BDMC-loaded self micro-emulsifying system (BDMC-SMEDDS). Solubility and compatibility tests, pseudo-ternary phase diagrams (PTPDs) as well as d-optimal concept was applied to design the formulation. The assessment of the prepared BDMC-SMEDDS in-vitro mainly included droplet size (DS) and entrapment efficiency (EE) determination, morphology, drug release and stability testing. Besides, the in vivo behavior was also evaluated after oral administration of BDMC-SMEDDS to rats. The optimal formulation was found to compose of Kolliphor EL (K-EL, emulsifier, 645.3mg), PEG 400 (co-emulsifier, 147.2mg), ethyl oleate (EO, oil, 207.5mg) and BDMC (50mg). The BDMC-SMEDDS with satisfactory stability had a mean size of 21.25±3.23nm and EE of 98.31±0.32%. Roughly 70% of BDMC was released from BDMC-SMEDDS within 84h compared with <20% from the free BDMC. More importantly, the in-vivo behavior of BDMC-SMEDDS showed that the AUC(0-12h) and plasma concentration of BDMC increased substantially as compared to the free BDMC. Altogether, BDMC-SMEDDS has the potential to enhance the solubility and bioavailability of BDMC and could be applied in the clinics.

Centrifugal Pumps as Extractors

AbstractThe generation of dispersions with defined droplet size distributions is important for liquid‐liquid extraction. In this respect, the capability of a centrifugal pump to generate dispersions was investigated for different operating points. For the analysis of the mixing process, a centrifugal pump was designed translucent. High‐speed images reveal the mechanism of particle breakup. Optical measurement technology and image processing with neural networks were used to determine droplet size distributions. The influence of flow rate, rotational frequency and holdup are discussed for a paraffin oil‐water system.

Effect of dilution on particle size analysis of w/o emulsions by dynamic light scattering

Dynamic Light Scattering (DLS) is a well-known (sub)micron particle size analysis technique. As such, it should be a valuable technique for water droplet size determination in (sub)micron water-in-oil emulsions. In this study, the sample pretreatment conditions were optimized in order to enable accurate droplet size determination by DLS. Whereas DLS was indeed capable of detecting differences between differently produced (sub)micron sized w/o emulsions, it was observed that the estimated droplet size was highly influenced by the measurement conditions used. First of all, the experimentally determined diffusion coefficient decreased with increasing water droplet concentration, which is thought to be due to interaction effects between the water droplets. To minimize this effect, the used concentration should be as low as possible. However, in doing so, the water droplets were frequently observed to disappear during storage or even during analysis, due to their dissolution in the dilution medium. The latter disturbing effect could be avoided by (sufficient) water saturation of the dilution medium and preventing water evaporation by closing the diluted sample and by restricting the head space. Summarizing, (sub)micron water droplets can be characterized using DLS. However, careful selection of the sample preparation and measurement conditions is necessary to obtain reliable data.

PH-sensitive Pickering Emulsion Stabilized by Hydroxyapatite Nanoparticles: Stability and Controlled Release Study

This study investigates the formulation of surfactant-free Pickering emulsions that release a drug at a specific pH to improve its oral bioavailability. The stabilizing nanoparticles composed of hydroxyapatite were obtained by a process of nanoprecipitation. Pickering oil-in-water emulsions stabilized with hydroxyapatite nanoparticles and encapsulating a hydrophobic drug model (ibuprofen) were formulated using a high-energy process with rotor-stator turbo mixer (IKA® T25 digital ultra-Turrax). The experimental approach explored the impact of all formulation parameters, dispersed phase and amount of hydroxyapatite nanoparticles on the physicochemical properties of Pickering emulsions. The system was characterized by a methylene blue test, pH and conductivity measurements, and droplet size determination. In addition, Pickering emulsions stabilized by hydroxyapatite nanoparticles have the advantage of being destabilized in acidic medium leading to the release of the active principle via the droplets. The acidic medium release study (pH equal to 1.2) showed ibuprofen release as a function of initial droplet loading and saturation concentration. In the simulated intestinal medium at pH equal to 6.8, we found a better release of ibuprofen from emulsions that already had saturation in an acid medium. Thus, the interest of these Pickering emulsions lies on the fact that their non-toxicity and hydroxyapatite nanoparticles have advantage of being biocompatible because having the same mineral composition as bones and teeth. In addition, they allow destabilization of the emulsions and release of the drug. These emulsions not only protect patients from the side effects of acid-based drugs, but also contribute to increase the bioavailability of these acidic drugs.

Diameters and Velocities of Droplets Emitted From the Cu Cathode of a Vacuum Arc

The cathode spots of vacuum arcs emit material in the form of plasma as well as droplets. Generated by arcs burning at the first wall of fusion devices, the droplets may effectively contaminate the fusion plasma. Essential characteristics of the droplets (diameter, velocity, and emission direction) and their interrelations are poorly known so far. In this paper, a new approach of optical droplet investigation is presented. Emitted from a pulsed vacuum arc, the droplets fly vertically inside a drift tube against gravity, finally passing two consecutive light beams. The time-of-flight and the detected intensity of scattered light allow a simultaneous determination of droplet velocity and size. Different solid angle directions have been realized by turning the cathode with respect to the flight tube axis. Using this technique, the parameters of droplets emitted from a Cu cathode into different directions were obtained. Two distinct groups could be identified at smaller ( 20°) angles between the surface plane and emission direction, respectively. They exhibit different velocity distributions and different relations between the particle diameter and the emission velocity.

Application of Acoustic Spectroscopy to the Characterization of Surfactant Solutions, Emulsions, and Microemulsions: d–Limonene–Water–C12EO7–Isopropanol System

AbstractThe application of acoustic spectroscopy to the characterization of binary C12EO7—water system was studied. It was discovered that the size of micelles in aqueous surfactant solutions could not be determined, but it was possible to determine the size of water nanodomains existing in the surfactant‐rich systems. It was suggested that in colloidal systems, the energy of ultrasonic waves is dissipated only by interfaces existing between condensed phases. The characterization of Winsor transitions by acoustic spectroscopy in water/d‐limonene system stabilized by a mixture of nonionic surfactant and isopropyl alcohol (cosolvent) was also explored. In one study, systems with a constant d‐limonene to water weight ratio obtained in the course of titration of d‐limonene‐in‐water emulsion with increasing amounts of surfactant+alcohol were investigated. In another study, a balanced d‐limonene/water microemulsion was sequentially diluted with water and d‐limonene. The transition between Winsor I and Winsor IV systems was monitored in both cases. Droplet size distributions were calculated using different models for dispersed and continuous phase composition. It was demonstrated that the magnitude of acoustic scattering played a significant role in the ability to reliably determine droplet size distributions, and in particular to simultaneously observe nanometer‐size and micron‐size droplets in Winsor I systems. An attempt was made to account for intrinsic attenuation of surfactant and alcohol by associating them with the aqueous phase, but this approach was shown not to be applicable in the case of Winsor IV microemulsions.

Performance tuning of microfluidic flow-focusing droplet generators.

The required step in all droplet-based devices is droplet formation. A droplet generator must deliver an application-specific performance that includes a prescribed droplet size and generation frequency while producing monodisperse droplets. The desired performance is usually reached through several cost- and time-inefficient design iterations. To address this, we take advantage of a low-cost rapid prototyping method and provide a framework that enables researchers to make informed decisions on how to change geometric parameters and flow conditions to tune the performance of a microfluidic flow-focusing droplet generator. We present the primary and secondary parameters necessary for fine-tuning droplet formation over a wide range of capillary numbers and flow rate ratios. Once the key parameters are identified, we demonstrate the effect of geometric parameters and flow conditions on droplet size, generation rate, polydispersity, and generation regime. Using this framework, a wide range of droplet diameters (i.e., 30-400 μm) and generation rates (i.e., 0.5-800 Hz) was achieved.

Magnetic resonance diffusion measurements of droplet size in drilling fluid emulsions on a benchtop instrument

Oil-based drilling fluids are complex emulsio-dispersions used in the construction of subsurface wellbores. Design and control of the rheological properties are crucial for successful drilling operations because the fluid performs several critical functions, such as hole cleaning (particle transport) and ensuring wellbore stability. One of the physical characteristics of the fluid that relates to rheology is the size of the water-in-oil emulsion droplets. Here we demonstrate the use of nuclear magnetic resonance (NMR) pulsed field gradient (PFG) diffusion measurements to determine droplet size distributions in oil-based drilling fluid analogues and a commercial formulation. NMR PFG allows these optically opaque samples to be measured without dilution, and the measurement is sensitive only to the liquid components. Although the NMR technique is established, the application to drilling fluids is novel. Through simulation and experiment, the suitability of a low-field benchtop NMR instrument (commonly used for rock core analysis in the petroleum industry) for measuring droplet size distributions in these fluids is explored. Despite limitations on the available gradient strength and the bulk diffusion coefficient of the brine, droplet radii in the range a = 1 μm to 50 μm are measured. The low-field NMR instrument is shown to be suitable for characterizing drilling fluids and similar complex emulsions.

Fabrication of Millimeters-Sized Poly(Divinylbenzene) Foam Shells from Controllable Double Emulsion in Microfluidic Device

A geometrically confined dripping was employed to enable precise control over the dimension and structure of millimeters-sized double-emulsion precursors of poly(divinylbenzene) foam shells in a new kind of double Y-shaped compound channels. Due to the 3D axial-symmetric microfluidic device, a more stable and robust flow field was maintained to obtain a continuous and regular emulsification. Various factors were systematically investigated for the precise size control of dripping in confined channel geometry, such as outlet channel size, fluid properties and flow rates. It was seen that phase properties and synergistic effects of main factors played key roles in determining droplet size. Thus, we used the optimized microfluidic approach to fabricate predetermined size foams to satisfy inertial fusion energy experiments, ranging from 4 to 4.6[Formula: see text]mm in diameter with a 50–300[Formula: see text][Formula: see text]m wall thickness and a coefficient of variation [Formula: see text]%. The results presented in this work provided a practical guideline for creating size-desired polymersome from comparable double emulsions.

Peanut-inspired anisotropic microparticles from microfluidics

Abstract With numerous unique properties, anisotropic particles which have non-spherical morphologies have intriguing great attention in recent years. Here, anisotropic microparticles with the shape of peanuts were fabricated through a novel microfluidic strategy, including microfluidic generation of droplet-containing fiber matrices and deformation of the droplets induced by stretching the fiber matrices. Droplets were emulsified in the microfluidic device system, in which flow rates were precisely controlled to determine droplet size and structure. Through stretching the elastic fibers, encapsulated droplets were able to be deformed into peanut-like shapes, with their interconnected cores well-aligned in correspondence to the stretching direction. Magnetic peanut-shaped particles could be obtained by incorporating magnetic nanoparticles , and showed extraordinary controllable ability under a changing magnetic field. In addition, the microparticles containing platinum and magnetic nanoparticles were generated and found being able to work as microstirrers. These features strongly attested the versatility and promising values of the peanut-inspired anisotropic microparticles in a broad range of application fields.

Multiphysics finite element modeling and validation of transient aerosol generation in an ultrasonic nebulizer drug delivery device

The purpose of this research is to study the process of ultrasonic aerosol generation by finite element modeling and validate it by experimental method. This understanding leads to downsize nebulization droplets and improve the drug delivery effectiveness. The finite element model of an ultrasonic nebulizer consists of a cylindrical chamber (filled with liquid), air, and a piezoelectric actuator at the bottom of the chamber. Many physical interactions including piezoelectric structural vibration, pressure acoustic in fluid, two-phase flow and droplet separation are analyzed and simulated. In validation, the ultrasonic nebulizer is attached to Andersen cascade impactor (ACI) with a vacuum pump for classifying the aerosol droplet size. The inductively coupled plasma optical emission spectrometry (ICP-OES) technique is used to determine droplet size distribution. The simulation results have shown that the major distribution of droplet size is in a range of 1.64–2.70 µm. Accordingly, the experimental results based on the ACI cutoff diameter stages depict that the major volume distribution of droplet size should be in a range of 1.10–3.29 µm. Submicron droplets (0.56–0.90 µm) are occurred in the simulation, and are also detected in the experiment at the ACI submicron cutoff diameters at 0.4 µm and 0.7 µm. This agreement has proved that the multiphysics model of the ultrasonic nebulizer can predict the size of generated aerosol. The relationship of ultrasonic nebulization parameters could be extended to conceive a new ultrasonic nebulizer design that would achieve submicron droplet size in rendering better drug delivery effectiveness.

Experimental investigation on GDI spray behavior of isooctane and alcohols at elevated pressure and temperature conditions

In this study macroscopic spray characteristics and droplet size distribution were measured for spray emanating from a six-hole solenoid GDI fuel injector. Three test fuels namely Isooctane, ethanol and n-butanol were used in this study. Macroscopic spray characterization was performed using Mie scattering and Schlieren Shadowgraph technique along with high speed videography. Liquid and vapor penetration length and along with the liquid/vapor spray cone angle was determined using these techniques. Phase Doppler Particle Analyzer (PDPA) was used to determine droplet size distribution. Results showed that thermo-physical properties such as saturation temperature, latent heat of vaporization, surface tension, density and viscosity of a fuel play a very important role in the spray plume penetration. Isooctane showed the least penetration lengths for all pressure and temperature conditions that were evaluated in this study, whereas butanol showed the highest penetration length. Due to the higher values surface tension, viscosity and latent heat of evaporation, alcohol sprays consisted of droplets of larger diameter.

Formulation and Evaluation of Lercanidipine Loaded Self-Nanoemulsifying Drug Delivery System

In the present study, we sought to improve the solubility and bioavailability of lercanidipine HCl using self-nanoemulsifying drug delivery systems (SNEDDS). The extent of self-emulsification was checked with various oils with suitable surfactants and co-surfactants. The final optimized formulation contained Caproyl 90, Tween 80 and Labrosol as oil, surfactant and co-surfactant respectively. Based on lercanidipine solubility analysis, ternary phase diagrams were constructed for optimizing the system. The formulations were evaluated for FTIR studies, scanning electron microscopy (SEM), solubility, droplet size determination, zeta potential and stability studies. The droplet size was found to be 5.1 nm and Z-Average of 14.6 nm. The zeta potential of the optimized formulation (F16) was found to be -19.7 mV. In vitro drug release from SNEDDS was significantly higher than pure drug. Hence, lercanidipine SNEDDS is an optimum formulation strategy to enhance the solubility and oral bioavailability of this poorly water-soluble drug.

Combination of sodium caseinate and succinylated alginate improved stability of high fat fish oil-in-water emulsions

Sodium caseinate (CAS) and commercial sodium alginate (CA), long chain modified alginate (LCMA) or short chain modified alginate (SCMA) were used in combination for emulsifying and stabilizing high fat (50–70%) fish oil-in-water emulsions. Physical (creaming, droplet size, viscosity and protein determination) and oxidative (primary and secondary oxidation products) stabilities of the emulsions were studied during 12 days of storage. Creaming stability was higher for emulsions produced with alginates and CAS compared to emulsions prepared with only CAS. Combined use of CAS + LCMA performed better in terms of physical stability compared to emulsions produced with only CAS. However, the oxidative stability of this emulsion was inferior probably due to the presence of an unsaturated carbon chain in LCMA structure. CAS + SCMA emulsions not only showed better physical stability such as smaller droplet size, lower creaming and higher viscosity, but also had an improved oxidative stability than emulsions produced with only CAS.

Determination of optimal parameters of rhamnolipid biosurfactant production: An agent for emulsification of heavy crude oil

ABSTRACTIn oil and petroleum industries, emulsification process is important to transfer and upgrade heavy oil. Rhamnolipids are the essential molecules of biosurfactants that used for this goal and they are often produced from various types of Pseudomonas aeroginosa bacteria. In this research, rhamnolipid biosurfactant produced from Pseudomonas aeroginosa ATCC 9027. The goal of this study was to optimize the effective parameters in production of rhamnolipid in order to reach the minimum water droplet size using Taguchi method. The evaluated parameters include incubation temperature, RPM of incubation, C/N ratio and pH of aqueous phase. Response parameters were yield, cost and water droplet size in water in oil (w/o) microemulsion. The results illustrated that the temperature of incubation and pH of the aqueous phase were the most effective factors in the production of rhamnolipid. Optimum operation condition including yield, cost and water droplet size, were 5.2 ± 0.1 g/l, 2.4 ± 0.14 $/g and 70 ± 5%, respectively. Dynamic light scattering (DLS) analysis was used for determination of water droplet size. Also the emulsification index (E24) of (w/o) emulsion was 98% ± 4. The results of this study could reduce the cost of rhamnolipid production for the applications in oil industries.

Computational study of droplet breakup in a trapped channel configuration using volume of fluid method

Computational Fluid Dynamics is performed to numerically investigate the droplet breakup of water in oil in trapped channel configuration. The volume-of-fluid (VOF) method based the commercial code FLUENT is adopted to track the interface. Two designs are suggested to study the effect of flow conditions parameters and outer channel size on the droplet breakup mode, droplet generation frequency and size. As a function of the velocity ratio, droplets are formed in two modes, dripping mode: droplets were generated closed to the nozzle, it was identified at low capillary number (Ca < 0.005) and jetting mode: droplets were produced after a long jet, where the capillary number Ca varies from 0.01 to 0.025. The numerical results indicated the collection channel diameter plays potential role in the determination of droplet size and droplet generation frequency, the shear forces excreted by the continuous phase on the dispersed thread are reduced in the wider model leading to have droplets much bigger than the narrow model, the latter produced small droplets due the high shear stress generated in the confinement region. Furthermore, the droplet frequency and size are found to be strongly dependent on the capillary velocity ratio. However, increasing the flow velocity ratio in both models leads droplets to be generated in high frequency, while the droplet length was decreasing. This work also demonstrates that the VOF method is an effective way to simulate the droplets breakup in trapped channel geometry.

Casein gel particles as novel soft Pickering stabilizers: The emulsifying property and packing behaviour at the oil-water interface

The aim of this study was to create food-grade soft gel particles that stabilize oil-in-water emulsions. The gel particles were prepared by covalently crosslinking the protein network within the self-associated casein sub-micelles (CN-GP) or calcium-induced casein micelles (CN-Ca-GP) with genipin. The mean diameters of CN-GP and CN-Ca-GP were 17.6 ± 2.9 nm and 113.5 ± 1.4 nm, respectively. From the atomic force microscopy images, it can be found the height of the two particles on the mica plate surface were significantly smaller than their width, indicating both the CN-GP and CN-Ca-GP were soft particles. Their ability to stabilize the oil droplets against creaming, coalescence and flocculation was assessed with Turbiscan analysis, droplet size determination and microscopy observation. For comparison, sodium caseinate (CN) was used as the control. The microscopy observation suggested the oil droplets stabilized by CN exhibited obvious flocculation, whereas the oil droplets stabilized by CN-GP or CN-Ca-GP were quite stable against flocculation. Turbiscan analysis showed the emulsions stabilized by CN-GP or CN-Ca-GP exhibited higher stability against creaming than the emulsions stabilized by CN. The droplet size determination indicated no significant changes in the average size of the oil droplets stabilized by CN-GP or CN-Ca-GP during 30 days’ storage, whereas significant increase in the average size of the oil droplets stabilized by CN can be observed during the storage. Cryo-scanning electron microscopy images suggested the CN-GP or CN-Ca-GP can be closely packed and deformed at the interfaces of the oil droplets. Overall, casein gel particles offer promising prospects in food emulsion-based products.