Submicron Droplets Research Articles

Abnormally strong decrease in reflectance of molten copper due to possible generation of levitating sub-micron melt droplets

A strong decrease in reflection of a probe laser radiation at wavelength 0.66µm from the surface of molten copper in argon atmosphere is observed in laboratory experiments for the first time. Theoretical estimates based on the Mie theory indicated that this effect can be qualitatively explained by a condensation of copper vapor leading to formation of sub-micron droplets levitating above the sample. This physical model is supported by the observed diffuse scattering of incident radiation and also by a regular structure of small crystals on solid sample surface after its cooling. This structure is similar to a solidified cluster of melt droplets after the crystallization of single droplets of copper melt and subsequent growth of the crystals.

Effects of capillarity on pool boiling using nano-textured surfaces through electrosprayed BiVO4 nano-pillars

Pool boiling is a mechanism by which heat is removed by changing the phase of a coolant from liquid to vapor. Surface wettability, which drives coolant capillarity, has a profound effect on the boiling process. We demonstrate pool boiling enhancement through wettability control using electrosprayed, nano-textured surfaces of bismuth vanadate (BiVO4). When a BiVO4 liquid precursor is electrostatically charged and sprayed, submicron droplets are formed and their acceleration is driven by the electrostatic force established between the nozzle exit and substrate. As droplets approach the substrate, Brownian diffusion takes place and an opposing thermophoretic force impedes the dynamic motion of evaporating droplets. As a result, nano-pillars are formed, whose physical sizes change the wettability of a surface and change pool-boiling phenomenon. The surface wettabilities of nano-textured surfaces were quantified with the water contact angle. Increased spraying time resulted in greater nano-pillar structure heights. Both the critical heat flux and effective heat transfer coefficient increased with nano-pillar height. However, excessively tall pillars had an adverse effect on pool-boiling through trapping of nucleated bubbles near the heat surface, which hindered efficient heat transfer.

Effects of tip streaming on the prediction of droplet size distribution in the presence of dispersants during subsea blowouts

Abstract (2017-193) With the presence of surfactants in the fluid mixture, tip streaming phenomenon often occurs where daughter droplets of micron or sub-micron size are ejected from thin threads of the droplet poles. Recent experimental and modeling studies of tip streaming phenomenon have been focusing on the formation of individual droplets. However, effects of tip streaming on the prediction of droplet formation during subsurface oil blowouts have not been thoroughly investigated. Due to the high intensity flow in the blowout, the amount of micron or sub-micron size droplets resulting from tip streaming could be substantial and cannot be ignored. In this study, a new empirical-numerical scheme is developed in the thoroughly-validated droplet formation model, VDROP-J, to account for the tip streaming phenomenon when dispersants are presence. Calibration of the new scheme and model validations are performed in association with the underwater oil jet experiments. The new model development improves the capability of VDROP-J model in application to the cases when dispersants are used, which would provide valuable information of droplet formation during subsea blowouts for decision makers and research groups.

Progress in the Formulation of Concentrated Ecological Emulsions for Agrochemical Application Based on Environmentally Friendly Ingredients

Researchers are engaged in exploring new ecological solvents for different applications, in accordance with the current trends in green chemistry and green engineering. This study is focused on the development of stable emulsions using eco-friendly ingredients, such as two green solvents as dispersed phase (N,N-dimethyl decanamide and α-pinene) and a nonionic polyoxyethylene glycerol ester derived from coconut oil as emulsifier. α-Pinene is a renewable essential oil that could find numerous agrochemical applications. In this investigation, we study the influence of dispersed phase concentration on droplet size distribution, physical stability, and rheological properties of highly concentrated eco-friendly emulsions. The laser diffraction technique revealed submicron droplet sizes for all studied emulsions. A coalescence process was detected in the most concentrated emulsions, not only by laser diffraction measurements, but also by rheology. Increasing the dispersed phase concentration from 30 to 45 wt % y...

Engineering of layered, lipid-encapsulated drug nanoparticles through spray-drying

Drug-containing nanoparticles have been synthesized through the spray-drying of submicron droplet aerosols by using matrix materials such as lipids and biopolymers. Understanding layer formation in composite nanoparticles is essential for the appropriate engineering of particle substructures. The present study developed a droplet–shrinkage model for predicting the solid-phase formation of two non-volatile solutes-stearic acid lipid and a set of drugs, by considering molecular volume and solubility. Nanoparticle formation was simulated to define the parameter space of material properties and process conditions for the formation of a layered structure with the preferential accumulation of the lipid in the outer layer. Moreover, lipid–drug demarcation diagrams representing a set of critical values of ratios of solute properties at which the two solutes precipitate simultaneously were developed. The model was validated through the preparation of stearic acid–isoniazid nanoparticles under controlled processing conditions. The developed model can guide the selection of solvents, lipids, and processing conditions such that drug loading and lipid encapsulation in composite nanoparticles are optimized.

α-Tocopherol as functional excipient for resveratrol and coenzyme Q10-loaded SNEDDS for improved bioavailability and prophylaxis of breast cancer

The present study evaluates the prophylactic efficacy of α-tocopherol (α-TOH), resveratrol (RES), and coenzyme Q10 (CoQ10) co-loaded self-nanoemulsifying drug delivery system (α-TOH-RES-CoQ10 SNEDDS) in 7,12-Dimethylbenz[a]anthracene (DMBA) induced breast cancer model. SNEDDS formulation components were rationally selected and optimized for maximum drug loading by applying the design of experiments and further evaluated for stability in simulated gastrointestinal fluids, functional stability of antioxidants, in vitro release, Caco-2 cell uptake, oral bioavailability and prophylactic anticancer activity. The SNEDDS demonstrated excellent stability in stimulated gastrointestinal fluids. The functional activity of antioxidants was confirmed by 2,2-diphenylpicrylhydrazyl (DPPH) scavenging assay wherein significantly (p > .05) higher antioxidant activity was observed in case of SNEDDS as compared with free antioxidants. Coumarin 6 (C-6)-loaded SNEDDS formulation demonstrated remarkably higher Caco-2 cell uptake in comparison with free C-6, indicative of efficient internalization of sub-micron SNEDDS droplets by Caco-2 cells. In line with Caco-2 cell uptake observations, α-TOH-RES-CoQ10-SNEDDS showed ∼2.30- and ∼3.64-fold increase in the AUC0−∞ values of RES and CoQ10 in comparison with free antioxidants. Significantly lower (p < .001) tumor volume (∼327 mm3) was found in case of animals treated with α-TOH-RES-CoQ10-SNEDDS in comparison with free antioxidant combination (∼1070 mm3) and DMBA control (∼1540 mm3) groups. Conclusively, the proposed strategy posed great potential in improving the prophylactic activity of antioxidants and hold promise for further exploration.

Formation of surface nanodroplets of viscous liquids by solvent exchange.

Surface nanodroplets are essential units for many compartmentalised processes from catalysis, liquid-liquid reactions, crystallization, wetting and more. Current techniques for producing submicron droplets are mainly based on top-down approaches, which are increasingly limited as scale reduces. Herein, solvent exchange is demonstrated as a simple solution-based approach for the formation of surface nanodroplets with intermediate and extremely high viscosity (1 000 000 cSt). By solvent exchange, the viscous droplet liquid dissolves in a good solvent that is then displaced by a poor solvent to yield surface droplets for the oversaturaion pulse at the mixing front. Within controlled flow conditions, the geometry of droplets of low and intermediate viscosity liquids can be tailored on the nano and microscale by controlling the flow rate. Meanwhile for extremely viscous liquids, the droplet size is shown to be dependent on the liquid temperature. This work demonstrates that solvent exchange offers a versatile tool for the formation of droplets with a wide range of viscosity.

In vitro characterization studies of self-microemulsified bosentan systems

Context: Bosentan is a poorly soluble drug and pose challenges in designing of drug delivery systems.Objective: The objective of this study is to enhance the solubility, dissolution and shelf-life of bosentan by formulating it as S-SMEDDS capsules.Materials and methods: Solubility of bosentan was tested in various liquid vehicles such as oils (rice bran and sunflower), surfactants (span 20 and tween 80) and co-surfactants (PEG 400 and propylene glycol) and microemulsions were developed. Bosentan was incorporated into appropriate microemulsion systems which were previously identified from pseudo ternary phase diagrams. Bosentan-loaded SMEDDS were evaluated for drug content, drug release, zeta potential, and droplet size. The selected liquid SMEDDS were converted into solid SMEDDS by employing adsorption and melt granulation. Solid SMEDDS were characterized for micromeritics and evaluated for drug content, drug release, and shelf-life.Results: Isotropic systems R5, R13, S5, and S13 with submicron droplet size had exhibited 85.45, 94.12, 81.67, and 96.64% drug release, respectively. Solid SMEDDS of MR13 and AS13 formulations with rapid reconstitution ability, exhibited 84.85 and 86.74% of on par drug release. The formulations were physicochemically intact for 1.02 and 1.56 years.Discussion: Liquid SMEDDS composed with PEG400 had displayed optimal characters. Solid SMEDDS had high-dissolution profiles than bosentan due to modification in the crystalline structure of drug upon microemulsification.Conclusion: Thus, solid SMEDDS addressed the solubility, dissolution, and stability issues of bosentan and becomes an alternate for clinical convenience.

A collection system for dry solid residues from exhaled breath for analysis via atomic force microscopy

Exhaled air contains sub-micron droplets of lung liquid, which potentially bear biomarkers of lung diseases. After dehydration they form dry residue particles (DRPs). As a first step in developing techniques to characterize individual DRPs, a new electrostatic collector was designed in which DRPs are charged within a unipolar corona charger, concentrated in a cone funnel, and deposited onto a limited area of a highly oriented pyrolytic graphite surface. The collector captures 80%–90% of DRPs at an optimal flow rate of 0.15 l min−1. Atomic force microscopy (AFM) revealed flattened round particles 20–50 nm high, with notable protrusions at their surface suggestive of an inhomogeneous internal structure. Exposure to humid air resulted in the DRPs spreading over the surface, with a 50%–200% decrease in their heights and an increase in their lateral dimensions so that their volume decreased by only 10% ± 3%. Exposure to saturated chloroform vapor resulted in drainage of 10%–15% of the DRP volume (presumably lipids), forming collar-shaped rings around each particle but leaving the core size and structure unchanged. AFM measurements combined with laser counter measurements of the DRP concentrations were used to estimate that one liter of air exhaled by volunteers contained less than 100 pg of dry residue material.

Evaluation of aggregate and silicone-oil counts in pre-filled siliconized syringes: An orthogonal study characterising the entire subvisible size range

Characterisation of particulates in therapeutic monoclonal antibody (mAb) formulations is routinely extended to the sub-visible size-range (0.1–10μm). Additionally, with the increased use of pre-filled syringes (PFS), particle differentiation is required between proteinaceous and non-proteinaceous particles such as silicone-oil droplets. Here, three orthogonal techniques: Raster Image Correlation Spectroscopy (RICS), Resonance Mass Measurements (RMM) and Micro-Flow Imaging (MFI), were evaluated with respect to their sub-visible particle measurement and characterisation capabilities. Particle formation in mAb PFS solutions was evaluated with increasing polysorbate-20 (PS-20) concentrations. All three techniques provided complementary but distinct information on protein aggregate and silicone-oil droplet presence. PS-20 limited the generation of mAb aggregates during agitation, while increasing the number of silicone-oil droplets (PS-20 concentration dependant). MFI and RMM revealed PS-20 lead to the formation of larger micron-sized droplets, with RICS revealing an increase in smaller sub-micron droplets. Subtle differences in data sets complicate the apparent correlation between silicone-oil sloughing and mAb aggregates’ generation. RICS (though the use of a specific dye) demonstrates an improved selectivity for mAb aggregates, a broader measurement size-range and smaller sample volume requirement. Thus, RICS is proposed to add value to the currently available particle measurement techniques and enable informed decisions during mAb formulation development.

Evaluation of an automated room decontamination device using aerosolized peracetic acid.

Because manual cleaning is often suboptimal, there is increasing interest in use of automated devices for room decontamination. We demonstrated that an ultrasonic room fogging system that generates submicron droplets of peracetic acid and hydrogen peroxide eliminated Clostridium difficile spores and vegetative pathogens from exposed carriers in hospital rooms and adjacent bathrooms.

Design of transmission-mode measurements for estimating ultrasound attenuation and nonlinearity in liver

Previously, it has been shown that ultrasound measurements of sound speed and nonlinearity can be used to quantify the fatty and non-fatty components of liver tissue. In addition, it has been proposed that ultrasound attenuation measurements can be used to distinguish fatty components comprising either sub-micron lipid droplets (microsteatosis) or much larger cell-sized droplets (macrosteatosis). To perform all of these measurements, a caliper device is being developed based on a transmission-mode approach. Design challenges are posed by competing requirements: sub-megahertz frequencies for optimal detection of microsteatosis and nonlinearity estimation based on waveform distortion over relatively short distances. To meet these challenges, a design is proposed in which ultrasound at 667 kHz is generated by a 50 mm piezoceramic disk and all measurements are made in the plane-wave regime. Given geometrical and physical constraints, all analysis was performed in the time domain. The nonlinearity coefficient ...

An emulsification system using a microchannel and a piezoelectric transducer

Ultrasonic emulsification devices have been used in many industrial and scientific fields. Recently, a nanoemulsion which contains small droplets having a diameter of sub-micron scale have attracted attentions. In usual, those emulsions are produced by using ultrasonic transducers oscillated to generate a cavitation field. However, such process has a difficulty to avoid contaminations. For a continuous process, we have generated the nanoemulsion by using microchannel devices and a piezoelectric transducer. The devices are made of stainless steel mainly. The micron-size droplets generated by a Y-type or T-type microchannel device, and are oscillated by a piezoelectric transducer in another microchannel device. The driving frequency of the transducer is over 2.2 MHz. We have succeeded in generating sub-micron size droplets which contain anti-cancer drug using this emulsification system. Additionally, we have evaluated the acoustic field in the microchannel by using a micro cavitation sensor. The micro sensor made of a piezoelectric polymer has been installed in the device. The sensor consists of some films deposited and patterned with a photolithography process. Using this sensor, the acoustic state in the microchannel has been evaluated from the acoustic power spectrum. From the results, we can conclude that the cavitation effect is not dominant in the emulsification process by this system.

Atomization of liquids by disintegrating thin liquid films using gas jets

Liquid atomization is useful in many applications, such as engineering, science, pharmaceutics, medicine, forensics and others. In the present research, an innovative methodology and a new device for atomization of liquids into mists of micron and submicron droplets have been developed. The new liquid-atomization method exploits the physical phenomenon of fragmentation of thin liquid films into fine micron and submicron droplets by gas jets. For several tested prototypes, the direct observations using a high-speed visualization technique have demonstrated that bubbles were generated within a liquid and their shells have been subsequently destroyed by applying a mechanical impulse (pressure of a compressed air) once the bubbles came over the liquid surface. The main characteristics of the generated tap water mists have been experimentally measured by means of the laser diffraction technique under various conditions for each prototype. One of the prototype devices allowed obtaining mists containing 90–99% of droplets smaller than 1µm, with the minimum arithmetic and Sauter mean droplet diameters of 1.48µm and 2.66µm, and the 2.64ml/min of droplet flow rate for 3.5bar manometer pressure of atomizing air. The gas to liquid mass ratios (GLR) in the new device are depending on the atomizing tube length and the number of perforated orifices in the tube: more the tube length, hence more the number of perforated orifices, and therefore more liquid droplets will form for the same gas flow rate. The measured GLR values related to 1m length of the utilized atomizing tube were in the range of 0.65–1.06, and for the specifically utilized atomizing tube of 72mm length were among 9.07–14.67. The results of this study demonstrate that the developed method of generation of very fine droplet mists has many advantages over the existing techniques and can be perspective for many practical applications.

Possibilities of optical remote sensing of dispersed oil in coastal waters

This study is intended to be one of the first steps in assessing the feasibility of remote sensing of dispersed oil in seawater. All optically active seawater constituents, including oil droplets, shape the water-leaving light flux and contribute to a commonly measured apparent optical variable known as remote sensing reflectance (Rrs). Radiative transfer simulations were performed in visible bands for natural seawater in the coastal zone of the Southern Baltic Sea and for a model of seawater polluted by dispersed Petrobaltic crude oil characterised by different droplet size distributions. Our model was supplied by simultaneous in situ measurements of inherent optical properties and the Rrs of natural seawater. The optical description of dispersed oil was based on previous experiments and new application of the Mie solution to the Petrobaltic crude oil of a log-normal size distribution characterised by peak diameters ranging from 0.5 to 500 μm. The results of radiative transfer modelling showed that the typically considered concentration of 1 ppm of oil droplets can locally affect the remote sensing reflectance, causing up to a 6-fold increase or 2-fold decrease, depending on the droplet size distribution. It was demonstrated that the optically significant oil droplet sizes (giving at least 5% contribution to the total scattering coefficient) are <100 μm, as long as oil concentration does not exceed 5 ppm. Moreover, we discussed the influence of dispersed oil droplets on the performance of remote sensing algorithms based on absolute Rrs values or band ratios. Oil dispersion that consists mostly of submicron droplets in a concentration of 1 ppm had the ability to increase blue/green Rrs ratios up to 32%, whereas oil dispersions dominated by micrometre-sized droplets tended to decrease such ratios by up to 18%. Blue/red Rrs ratios were most strongly affected by dispersed Petrobaltic oil, causing a 9%–54% decrease for droplet size distributions characterised by a peak diameter of up to 100 μm. These findings demonstrate why these parameters are considered to be the most useful in the potential remote sensing algorithms.

Acoustic forces acting on particles and fluids in microscale acoustofluidics

Acoustofluidics relying on acoustic forces to handle fluids and particles in microfluidic systems has emerged as a useful tool for characterizing, focusing, separating, and sorting cells based on their acousto-mechanical properties. Here, we present recent advances in the theoretical understanding of acoustic forces on particles and fluids. In particular, we address the effects of thermoviscous boundary layers on acoustic scattering off sub-micron particles or droplets. Re-examining the far-field method of calculating acoustic radiation forces and torques, we show that exact non-perturbative expressions can be derived regardless of boundary layer dissipation. The necessary condition for moving the surface of integration from the particle surface to the far field, is the time-periodicity of the system rather than negligible boundary-layer dissipation. In the long-wavelength limit, this approach leads to particularly simple expressions for the force and torque acting on a particle in a thermoviscous fluid. ...

Formation of copper tin sulfide films by pulsed laser deposition at 248 and 355 nm

The influence of the laser wavelength on the deposition of copper tin sulfide (CTS) and SnS-rich CTS with a 248-nm KrF excimer laser (pulse length τ = 20 ns) and a 355-nm frequency-tripled Nd:YAG laser (τ = 6 ns) was investigated. A comparative study of the two UV wavelengths shows that the CTS film growth rate per pulse was three to four times lower with the 248-nm laser than the 355-nm laser. SnS-rich CTS is more efficiently ablated than pure CTS. Films deposited at high fluence have submicron and micrometer size droplets, and the size and area density of the droplets do not vary significantly from 248 to 355 nm deposition. Irradiation at low fluence resulted in a non-stoichiometric material transfer with significant Cu deficiency in the as-deposited films. We discuss the transition from a non-stoichiometric material transfer at low fluence to a nearly stoichiometric ablation at high fluence based on a transition from a dominant evaporation regime to an ablation regime.

Melt rheology and mechanical crystal transformation in an immiscible blend with poly(vinylidene fluoride) matrix

ABSTRACTEffect of immiscible polyamide 6 (PA6) on the melt rheology and stretch‐induced crystal transformation of poly (vinylidene fluoride) (PVDF) matrix is reported. PA6 is dispersed as submicron droplets in the PVDF matrix, responsible for significant enhancement in the melt elasticity. Nevertheless, crystallization habits of PVDF matrix from melt are little affected by submicron PA6 droplets, and the α‐form of PVDF prevails in the blends. Upon mechanical stretching, the α‐form is converted to the β‐form, which is remarkably reduced with the increasing of PA6 content in the blends. It could be correlated with the decreased tensile stress in the presence of submicron PA6 droplets that act as stress concentrators. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43499.

Investigation of splashing phenomena during the impact of molten sub-micron gold droplets on solid surfaces.

The dynamics of splashing accompanying the impact of molten 800 nm diameter gold droplets on silicon, gold coated silicon, gold coated glass and polished solid gold surfaces has been studied. A novel method based on laser induced forward transfer has been developed to generate single submicron molten gold droplets. Splashing morphology has been characterized using Scanning Electron Microscopy (SEM) and Focused Ion Beam (FIB) techniques. It is found that the splashing of submicron gold droplets upon impact is enhanced by high droplet impact energy achieved by reducing the droplet flight distance and that an air layer resulting in a bubble becomes trapped under the impacting droplets even when the size of the droplet is less than one micron. Our results show that, under these conditions, heat transfer between the submicron droplet and the solid substrate is more important than surface roughness and surface tension in the evolution of splashing. A theoretical model has been developed to simulate the splashing characteristics of submicron gold droplets during impact. Both the experimental data and the analytical model show that splashing is enhanced by high heat transfer rates to the surface.

Treatment of cutting-oily wastewater by electrocoagulation-flotation (ECF) process: Modeling approach

This work aims to investigate the oily wastewater treatment by the electrocoagulation-flotation (ECF) and propose a mathematical model for the efficiency prediction. Cutting oil was used to prepare the synthetic oily wastewater with submicron droplet sizes. The chemical coagulation by aluminium sulfate was firstly tested following by the electrocoagulation-flotation with aluminium electrodes. Both processes gave the effective treatment performance with the efficiencies higher than 90%. However, the ECF consumed less aluminium dosage as well as produced less sludge, which were its advantage on the chemical coagulation. The performance of the ECF was found to be affected by the current density, oil concentration, and reaction time according to the analysis by the design of experiment (DOE). Finally, the prediction model was proposed by two approaches, including linear and logarithm function. The latter model gave more accuracy prediction results in terms of treatment efficiency and duration in the lag and stable stages. Keywords: Chemical coagulation, Cutting oily wastewater, Design of experiment (DOE), Electrocoagulation-flotation, Prediction model