Submicron Droplets Research Articles

Solvent emissions control in large scale chemical absorption CO2 capture plant

Solvent emissions is a serious problem in the industrialization of the amine scrubbing process. To design pollutant control equipment for a 2 million tons/year CO2 capture plant, a bench and a pilot facility were tested to investigate the aerosol emissions. And three Aspen models were built to study vapor emission and design emissions control measurement. The emissions assessment showed the treated flue gas after the absorber was about to discharge 1078 mg/Nm3 aerosol-type solvent and 1055 mg/Nm3 vapor-type solvent. The experimental results of particle size distribution indicated that improving the growth of the submicron droplets before the water wash and demister was the key to control aerosol emissions. Three control methods were compared by simulation, the best control measure was the combination of dry bed and water wash section, and the drain-out water is feed to the top of the dry bed. Considering the economy and control efficiency, the packing height of the water wash section is 2.5 m, and the scrubbing flow rate is 5000 Nm3/h. The extra cooling for the dry bed is not necessary and uneconomic. Under this countermeasure, the vapor emissions solvent is as low as 1.27 mg/Nm3 without additional freshwater for the water wash section.

Broadband X-ray generation by large krypton clusters under the effect of relativistic femtosecond laser pulses

This paper presents a phenomenological analysis of thermodynamic parameters of a pulsed supersonic gas jet in a conical nozzle. Conditions have been found out for the condensation and formation of large krypton clusters resulting from phase transitions during adiabatic expansion of gas through the nozzle into vacuum. We have identified the phase state of the large clusters (submicron droplets consisting of ∼107 monomers) forming in the jet and obtained a high yield of X-rays from a cluster nanoplasma produced by femtosecond laser pulses of relativistic intensity I. It has been shown that, at I ≈ 3 × 1018 W cm−2, a nanoplasma consisting of large krypton clusters emits a broadband X-ray spectrum in the range 5 – 100 keV. The integrated laser to X-ray energy conversion efficiency achieved is ∼10−5 (400 nJ), and the efficiency of characteristic Kα line (12.6 keV) generation is ∼1.5 × 10−6 (68 nJ), which corresponds to a quantum yield of ∼3 × 108 photons s−1 (4π)−1, with a contrast of ∼25 relative to bremsstrahlung background.

Droplet surface exposure measurement of a large splashing oil fume in the kitchen with a fluorescent 3D microscopic passive testing method

Cooking is a major source of indoor particulate matter, surpassing smoking. Large splashing oil fumes produced by water-oil interactions while cooking have received increasing attention for their common and significant hazards. However, the pollution of large splashing droplets is rather difficult to quantitatively measure with the current techniques. In this study, a fluorescent 3D microscopic passive testing method that is accurate and reliable for large spaces and broad-spectrum droplets is developed by combining fluorescence tracer, passive sampling, microscopic vision and droplet 3D reconstruction technologies. The measurement error for submicron droplets is approximately 22.6%. Because large droplet pollution is not unique to the kitchen, our innovative test method is worthy of reference in many fields, such as cleaning and painting workshops. We tested the surface exposure of a large splashing oil fume of 1–500 μm with this method. The results showed that the particle size of splashing oil droplets presents a bimodal distribution, which matches the two generation mechanisms that have been observed. The surface exposure mass concentration of all droplets of 1–500 μm on the surface at a distance of 0.75 m from the emission source edge is reduced to 3.6% of 0.25 m. Droplets (10–100 μm) are the main pollutants, which have continuous indirect hazards and require more attention.

Modeling Aerial Transmission of Pathogens (Including the SARS-CoV-2 Virus) through Aerosol Emissions from E-Cigarettes

We examine the plausibility of aerial transmission of pathogens (including the SARS-CoV-2 virus) through respiratory droplets that might be carried by exhaled e-cigarette aerosol (ECA). Given the lack of empiric evidence on this phenomenon, we consider available evidence on cigarette smoking and respiratory droplet emission from mouth breathing through a mouthpiece as convenient proxies to infer the capacity of vaping to transport pathogens in respiratory droplets. Since both exhaled droplets and ECA droplets are within the Stokes regime, the ECA flow acts effectively as a visual tracer of the expiratory flow. To infer quantitatively the direct exposure distance, we consider a model that approximates exhaled ECA flow as an axially symmetric intermittent steady starting jet evolving into an unstable puff, an evolution that we corroborate by comparison with photographs and videos of actual vapers. On the grounds of all this theoretical modeling, we estimate for low-intensity vaping (practiced by 80–90% of vapers) the emission of 6–210 (median 39.9, median deviation 67.3) respiratory submicron droplets per puff and a horizontal distance spread of 1–2 m, with intense vaping possibly emitting up to 1000 droplets per puff in the submicron range with a distance spread over 2 m. The optical visibility of the ECA flow has important safety implications, as bystanders become instinctively aware of the scope and distance of possible direct contagion through the vaping jet.

Impact of Microfluidization on the Emulsifying Properties of Zein-Based Emulsions: Influence of Diutan Gum Concentration.

Microfluidization is a preparation method that can be used to obtain emulsions with submicron droplet sizes. The first objective of this study was to evaluate the influence of homogenization pressure and cycles on droplet sizes using response surface methodology. Secondly, the influence of the diutan gum concentration incorporated in the optimized emulsion on rheological properties, microstructure, and physical stability was investigated. Taking the response surface analysis into account, the emulsion processed at 20,000 psi after four cycles seemed to show the smallest Sauter diameter values. Hence, this emulsion was the starting point to incorporate diutan gum. Interestingly, the formation of a 3D network in the emulsion, observed by FESEM, was provoked by diutan gum. The emulsion formulated with 0.4 wt.% of diutan gum presented rheological gel properties and enhanced physical stability. This work highlights the importance of selecting optimized processing variables using the microfluidization technique and extends the knowledge of using diutan gum in combination with zein.

MECHANICAL PROPERTIES OF POLYSULFONE-ZnO NANOCOMPOSITE MEMBRANE

Large quantities of wastewater are generated by the petroleum refining process. Micron-scale emulsion droplets and submicron droplets are difficult to remove from oil-refined wastewater, and addressing these issues has been a major challenge for researchers. Membrane technology is widely used in water treatment because it is very selective and effective in the filtration process. his research focuses on oil refinery water treatment using a polysulfone membrane (PSF)-nano-ZnO membrane with the addition of polyethylene glycol (PEG). This research aims to determine the PEG ratio that produces the optimum PSF-ZnO membrane in terms of mechanical properties, including thickness, tensile strength, and molecular weight cut-off (MWCO) value. The membranes with the optimum clearance were obtained at 3% PEG with a thickness of 0.0077 mm, Young's modulus of 8800 N/m2, and Morphological analysis was performed using the SEM (Scanning Electron Microscopy) method on the membrane which had the highest and lowest permeability values.. The best membrane MWCO value was achieved by the addition of 19% PSF-nano-ZnO 1% wt at 5 minutes of UV irradiation. This shows that the addition of PEG composite affects pore openings. The membrane formed with variations in PEG concentrations affecting the thickness of the membrane. Higher concentrations make the membrane thicker, resulting in a higher Young’s modulus.

Rheology of protein-stabilised emulsion gels envisioned as composite networks. 2 - Framework for the study of emulsion gels

HypothesisThe aggregation of protein-stabilised emulsions leads to the formation of emulsion gels. These soft solids may be envisioned as droplet-filled matrices. Here however, it is assumed that protein-coated sub-micron droplets contribute to the network formation in a similar way to proteins. Emulsion gels are thus envisioned as composite networks made of proteins and droplets. ExperimentsEmulsion gels with a wide range of composition are prepared and their viscoelasticity and frequency dependence are measured. Their rheological behaviours are then analysed and compared with the properties of pure gels presented in the first part of this study. FindingsWhen the concentrations of droplets and protein are expressed as an effective volume fraction, the rheological behaviour of emulsion gels is shown to depend mostly on the total volume fraction, while the composition of the gel indicates its level of similarity with either pure droplet gels or pure protein gels. These results help to form an emerging picture of protein-stabilised emulsion gel as intermediate between droplet and protein gels. This justifies a posteriori the hypothesis of composite networks, and opens the road for the formulation of emulsion gels with fine-tuned rheology.

Room Temperature Nanoencapsulation of Bioactive Eicosapentaenoic Acid Rich Oil within Whey Protein Microparticles.

In this study, emulsion electrospraying assisted by pressurized gas (EAPG) has been performed for the first time to entrap ca. 760 nm droplets of the bioactive eicosapentaenoic acid (EPA)-rich oil into whey protein concentrate (WPC) at room temperature. The submicron droplets of EPA oil were encapsulated within WPC spherical microparticles, with sizes around 5 µm. The EPA oil did not oxidize in the course of the encapsulation performed at 25 °C and in the presence of air, as corroborated by the peroxide value measurements. Attenuated Total Reflection—Fourier Transform Infrared spectroscopy and oxygen consumption tests confirmed that the encapsulated EPA-rich oil showed increased oxidative stability in comparison with the free oil during an accelerated oxidation test under ultraviolet light. Moreover, the encapsulated EPA-rich oil showed increased thermal stability in comparison with the free oil, as measured by oxidative thermogravimetric analysis. The encapsulated EPA-rich oil showed a somewhat reduced organoleptic impact in contrast with the neat EPA oil using rehydrated powdered milk as a reference. Finally, the oxidative stability by thermogravimetric analysis and organoleptic impact of mixtures of EPA and docosahexaenoic acid (DHA)-loaded microparticles was also studied, suggesting an overall reduced organoleptic impact compared to pure EPA. The results here suggest that it is possible to encapsulate 80% polyunsaturated fatty acids (PUFAs)-enriched oils by emulsion EAPG technology at room temperature, which could be used to produce personalized nutraceuticals or pharmaceuticals alone or in combination with other microparticles encapsulating different PUFAs to obtain different targeted health and organoleptic benefits.

Laser scattering by submicron droplets formed during the electrical explosion of thin metal wires

This paper presents the results of studying dispersed media formation during the electrical explosion of thin metal wires in vacuum by using low-current generators (∼1–10 kA). Particular attention is paid to the analysis of the composition and structure of the corresponding explosion products as well as to the problem of their visualization using simultaneous laser interferometry and shadow imaging at two wavelengths (1.064 µm and 0.532 µm). Our findings indicate the important role in the visualization of the explosion products that belongs to multiple scattering by submicron droplets of dense condensed matter, which are mixed with metal vapor. The hypothesis on the existence of submicron droplets in the products of exploding metal wires correlates with the results obtained by soft x-ray radiography combined with a laser probing technique. Taking into account the multiple scattering by submicron droplets, it is possible to significantly clarify the parameters of the explosion products visualized via laser probing techniques as well as to gain a deeper insight into the physics behind the electrical wire explosion.

Focused targeting of inhaled magnetic aerosols in reconstructed in vitro airway models

The pulmonary tract is an attractive route for topical treatments of lung diseases. Yet, our ability to confine the deposition of inhalation aerosols to specific lung regions, or local airways, remains still widely beyond reach. It has been hypothesized that by coupling magnetic particles to inhaled therapeutics the ability to locally target airway sites can be substantially improved. Although the underlying principle has shown promise in seminal in vivo animal experiments as well as in vitro and in silico studies, its practical implementation has come short of delivering efficient localized airway targeting. Here, we demonstrate in an in vitro proof-of-concept an inhalation framework to leverage magnetically-loaded aerosols for airway targeting in the presence of an external magnetic field. By coupling the delivery of a short pulsed bolus of sub-micron (~500 nm diameter) droplet aerosols with a custom ventilation machine that tracks the volume of air inhaled past the bolus, focused targeting can be maximized during a breath hold maneuver. Specifically, we visualize the motion of the pulsed SPION-laden (superparamagnetic iron oxide nanoparticles) aerosol bolus and quantify under microscopy ensuing deposition patterns in reconstructed 3D airway models. Our aerosol inhalation platform allows for the first time to deposit inhaled particles to specific airway sites while minimizing undesired deposition across the remaining airspace, in an effort to significantly augment the targeting efficiency (i.e. deposition ratio between targeted and untargeted regions). Such inhalation strategy may pave the way for improved treatment outcomes, including reducing side effects in chemotherapy.

Time Evolution and Effect of Dispersant on the Morphology and Viscosity of Water-In-Crude-Oil Emulsions.

This study examines the time evolution and effects of adding dispersant (Corexit 9500A) at varying concentrations on the microscopic morphology and bulk viscosity of saltwater-in-crude-oil (Louisiana) mechanically mixed emulsions. Rheology is used for measuring the viscoelastic properties and viscosity, the latter at varying shear rates. Microscopy, followed by machine-learning-based analysis, is used for characterizing the size and spatial distribution of the water droplets in the emulsions. Initially, the water droplets appear as a multiscale lattice with a Sauter diameter of 5.3 μm and a polydispersity of 0.43, with small droplets aggregating around large ones. The corresponding bulk viscosity decreases with increasing shear rate from 2 orders of magnitude to 5 times higher than that of the weathered crude oil. After 7 days, the number of submicron droplets increases, the nearest-neighbor distance decreases, indicating preferential aggregation, and the viscosity increases by 56-112% at high shear rates (5-100 s-1). After 14 and 21 days, some droplets coalesce resulting in loss of clusters and a decrease in viscosity. These trends suggest that changes in the aggregation contribute to the variations in viscosity. Subsequent analysis applies previously developed models for the effect of aggregation on the properties of the emulsion. While the reduction in viscosity is predicted by this model, matching of rates requires modification to the assumed relationship between yield stress and interdroplet forces. Adding dispersant without mixing generates Marangoni-driven flows as the water droplets coalesce. In time, part of the water separates, a fraction forms clouds of submicron droplets, and the rest remains unchanged. Mixing dispersant at low concentration with the emulsion accelerates the coalescence and phase separation. The removed water fraction increases with dispersant concentration, reaching 99.6% for a dispersant-to-emulsion concentration of 10-3. The remaining emulsion consists of fine droplets with Newtonian viscosity that is still 4 times higher than that of the fresh crude oil but only 14% higher than that of the weathered oil.

Experimental evidence that halogen bonding catalyzes the heterogeneous chlorination of alkenes in submicron liquid droplets.

A key challenge in predicting the multiphase chemistry of aerosols and droplets is connecting reaction probabilities, observed in an experiment, with the kinetics of individual elementary steps that control the chemistry that occurs across a gas/liquid interface. Here we report evidence that oxygenated molecules accelerate the heterogeneous reaction rate of chlorine gas with an alkene (squalene, Sqe) in submicron droplets. The effective reaction probability for Sqe is sensitive to both the aerosol composition and gas phase environment. In binary aerosol mixtures with 2-decyl-1-tetradecanol, linoleic acid and oleic acid, Sqe reacts 12–23× more rapidly than in a pure aerosol. In contrast, the reactivity of Sqe is diminished by 3× when mixed with an alkane. Additionally, small oxygenated molecules in the gas phase (water, ethanol, acetone, and acetic acid) accelerate (up to 10×) the heterogeneous chlorination rate of Sqe. The overall reaction mechanism is not altered by the presence of these aerosol and gas phase additives, suggesting instead that they act as catalysts. Since the largest rate acceleration occurs in the presence of oxygenated molecules, we conclude that halogen bonding enhances reactivity by slowing the desorption kinetics of Cl2 at the interface, in a way that is analogous to decreasing temperature. These results highlight the importance of relatively weak interactions in controlling the speed of multiphase reactions important for atmospheric and indoor environments.

Fast-ion-induced secondary ion emission from submicron droplet surfaces studied using a new coincidence technique with forward-scattered projectiles.

A mass spectrometric study of secondary ions emitted from droplet surfaces by MeV-energy heavy ion impact was performed to investigate fast-ion-induced molecular reaction processes on liquid surfaces. Herein, a new coincidence technique was developed between secondary ions and scattered projectile ions at a small forward angle. The advantages of this technique were demonstrated by measurement of the collision between 4-MeV C3+ and ethanol droplets. Secondary ion emission probabilities were obtained directly from the coincidence data. Notably, this technique enabled positive fragment ions that had not been identified in previous measurements to be observed by suppressing the strong background originating from gas-phase molecules more than 104-fold. H+, H3O+, C2H5 +, and C2H5O+ were found to be produced as major positive fragment ions, in addition to minor fragments H2 +, C2H3 +, and CH2OH+. Production of these ions suggests that competition between rapid hydrogen ion emission from multiply ionized states and intermolecular proton transfer accompanied by fragmentation through protonated ethanol occurs after fast heavy-ion collisions. Clarification of the positive fragment ions also revealed the characteristic features of negative ions. Negative ions were realized to exhibit higher degrees of fragmentation and reactivity compared with positive ions. Furthermore, the energy loss by forward-scattered ions during droplet penetration was used to evaluate the target thickness at a submicron level. Variations in secondary ion yield, mass distribution, and kinetic energies depending on the penetration length were observed below 1 µm. These results highlight the unknown mechanism of these "submicron effects" observed in secondary ion emission processes as a new phenomenon.

Superheated metastable water atomization: fine atomized water plumes diagnostics and disperse characteristics; summary of results, applications in power generation and new techniques.

Complex experimental investigation of superheated flow and dispersion characteristics of sprays in atomizing nozzles of various types is made. The comparative analysis of experimental and calculating investigations of thermo physic and hydro- gas-dynamic flow and disperse characteristics was carried out for various types of spray nozzles. It has shown that the main process, which determine peculiarities of superheated metastable water flow and phase transformation in spray nozzles, is quick (explosive) boiling up. And the optimal variant for superheated water atomization and achieving the most fine spray plumes, which contain mainly submicron droplet fraction, at initial temperature 240°C (and higher) is atomization by means of contracting-expanding nozzles. In such nozzles the explosive boiling is accomplished by quick transformation of foamed liquid into vapor-droplet flow. Diagnostic peculiarities are considered for these optically dense spray plumes; the auxiliary measurement methods were worked out for estimation superheated water high atomization level. The experimental and calculating data dimensionless treatment was made for achieving extremely fine (mainly submicron) superheated water spray. The dimensionless parameter, which determines necessary water (or some other liquids, for example – fuels) superheating level was derived. The possible technical applications of superheated water sprays are described, and up-to-date state of corresponding projects is given.

Evaluation of Novel “No-Touch” Technologies for Decontamination of Toys in Pediatric Healthcare Settings

Background: Toys in playrooms are often shared among patients in pediatric healthcare settings; they can present a risk for transmission of bacterial and viral pathogens. Effective cleaning and disinfection of toys using disinfectant wipes is labor intensive and difficult due to irregular surfaces. Methods: We conducted a point-prevalence culture survey to determine the frequency of contamination of in-use toys and high-touch surfaces in playrooms in a pediatric healthcare facility with methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), and Clostridioides difficile. Using a variety of toys inoculated with pathogens, we evaluated efficacy and ease-of-use of 3 novel “no-touch” technologies: (1) an electrostatic sprayer, (2) a small ultraviolet-C (UV-C) box (18.9 × 9.9 × 1.8 inches) for smaller toys, and (3) a high-level disinfection cabinet using ultrasonic submicron droplets of peracetic acid and hydrogen peroxide. Test pathogens included C. difficile, MRSA, and Candida auris. Results: Of 135 items cultured in playrooms, 6 (4.4%) were contaminated with MRSA, 1 (0.7%) was contaminated with VRE, and none were contaminated with C. difficile. Each of the technologies reduced all pathogens by >4 log10 CFU on all types of toys tested (plastic, soft rubber, and tablet). The electrostatic sprayer was considered the easiest to use by all users because large numbers of toys could be processed much more quickly (ie, spray for 20 seconds and allow to air dry) than with disinfectant wipes. The disinfection cabinet required 21 minutes for cycle completion, whereas the decontamination cycle for the UV box was only 30–90 seconds but with limited capacity to hold toys. Conclusions: Three “no-touch” technologies were effective for disinfection of toys contaminated with healthcare-associated pathogens. The electrostatic spray application of disinfectant was considered the easiest to use for rapid decontamination of toys.Funding: NoneDisclosures: None

Density enhancement of nano-sized and submicron-sized water droplets induced by charges released from corona discharge

Corona discharge is widely used as an ionization source in field experiments of weather modification induced by charged particles due to its high efficiency and economy. However, deficient research efforts have been devoted to the effects of corona discharge on the size distribution and evolution of droplets in the humid air. In this paper, the characteristic of water droplets spectrum evolution in humid air with unipolar corona discharge is studied by an electrical low pressure impactor (ELPI) experiment in a 96 m3 cloud chamber. Results show that nano-sized water droplets with diameters from 9 nm to 25 nm grow rapidly because of the inducement of charges released from corona discharge. Additionally, an increase in the concentration of submicron droplets appears at 20 min. To reveal the potential mechanism of the phenomena, the average charge values of charged droplets measured by ELPI are further analyzed. Meanwhile, the relationship between saturated vapor pressure over charged droplet’s surface and its radius is discussed by the modified Kelvin–Thomson equation. Results show that, for the density enhancement of nano-sized droplets, condensational growth induced by charges released from corona discharge dominates significantly. The subsequent increase in the density of submicron-sized droplets is regarded as the break-up of the micron-sized droplets, with the process of evaporation when droplets are approaching the Rayleigh limit in the sub-saturated environment. This research may bring some new perspectives to further study of weather modification and cloud-seeding induced by charged particles, such as by increasing condensed nuclei density, broadening cloud droplets spectrum, and suppressing the evaporation of cloud droplets, etc.

Rheology of protein-stabilised emulsion gels envisioned as composite networks 1– Comparison of pure droplet gels and protein gels

HypothesisProtein-stabilised emulsion gels can be studied in the theoretical framework of colloidal gels, because both protein assemblies and droplets may be considered as soft colloids. These particles differ in their nature, size and softness, and these differences may have an influence on the rheological properties of the gels they form. ExperimentsPure gels made of milk proteins (sodium caseinate), or of sub-micron protein-stabilised droplets, were prepared by slow acidification of suspensions at various concentrations. Their microstructure was characterised, their viscoelasticity, both in the linear and non-linear regime, and their frequency dependence were measured, and the behaviour of the two types of gels was compared. FindingsProtein gels and droplet gels were found to have broadly similar microstructure and rheological properties when compared at fixed volume fraction, a parameter derived from the study of the viscosity of the suspensions formed by proteins and by droplets. The viscoelasticity displayed a power law behaviour in concentration, as did the storage modulus in frequency. Additionally, strain hardening was found to occur at low concentration. These behaviours differed slightly between protein gels and droplet gels, showing that some specific properties of the primary colloidal particles play a role in the development of the rheological properties of the gels.

Ultrathin coating of particles in fluidized bed using submicron droplet aerosol

In this work, we demonstrate that particles can be coated in a fluidized bed with coating solution provided by a novel aerosol generator. Aerosol droplets are smaller than 1μm in volume-based diameter, hence they are very much smaller than droplets in conventional spray fluidized bed processes (around 40μm). A proof-of-principle experiment with 30% aqueous coating solution of sodium benzoate and γ-Al2O3 core particles in 150mm fluidized bed fed with droplet aerosol supplied from the chamber side is presented. To simultaneously coat and dry the particles, inlet of fluidization air was at 50°C. Moreover, Monte Carlo simulations of coating with small aerosol and large spray droplets were conducted. Due to dramatically smaller building blocks, ultrathin particle coating of high-resolution (very small layer thickness) can be attained with the new aerosol process, with the potential of even going nanoscale. Full coverage of particles is reached substantially faster than in the conventional process, so that material demand is much lower and sensitive materials can be processed in short residence time. Solids yield of around 30% was much higher than expected, that is considered to be technically viable and may be enhanced by the recycling of entrained solids or better equipment design.

Scalable preparation of hollow ZrO2 microspheres through a liquid-liquid phase reunion assisted sol-gel method

This study demonstrates the use of a liquid-liquid phase reunion (PR) assisted sol-gel method to prepare hollow ZrO2 microspheres. The oil phase of trichloroethylene and isooctanol mixture (TCE/IO), aqueous phase of the ZrO2 precursor sol, and co-solvent phase propylene glycol monomethyl ether (PGME) were mixed and vigorously stirred to form an emulsion with dispersed sub-micron TCE/IO-rich droplets, which do not aggregate and are stable in the long term. This emulsion was further dispersed in pure TCE/IO to form multicore microdroplets, wherein the inner sub-micron droplets grew unstable and coalesced as one (PR), this led to the transformation of the microdroplets from being multicore to single core. The resultant core-shell structure was stable over the duration of the gelation and the aging processes. Subsequently, hollow ZrO2 microspheres with cavities that could be size controlled were obtained by sintering. The method presented in this study is scalable for achieving an increased productivity due to the self-assembly fabrication of the core-shell droplets by using the liquid-liquid PR method.

Persistent thin water films encapsulate oil droplets crossing an oil-water interface

Understanding of oil-water interfacial phenomena is essential for predicting mixing and/or phase-separation in environmental and industrial systems. Time-resolved digital holography and planar laser-induced fluorescence are used for examining processes occurring after ascending buoyant oil droplets of varying viscosity cross a stratified oil-water interface. Previous studies have focused on the crossing process, and the current belief is that once this droplet becomes immersed in the oil, its content can mix with the bulk fluid. In contrast, we show that the droplets remain encapsulated by a stable continuous submicron thin water film, which prevent them from mixing. This film forms even in pure oil and water with minimal surfactant concentration and persists for periods that are three to four orders of magnitude longer than those of the crossing process. Observations following the film evolution reveal that segments located close to the interface appear to be attracted to the bulk water, causing the entire droplet to flatten slowly. The resulting reduction in the peripheral radius of curvature eventually breaks up the film into suspended submicron droplets. The morphology of this flattening process varies with oil viscosity, and its duration increases from seconds to nearly one hour as the oil viscosity increases from one to fifty cSt. In processes involving multiple oil droplets crossing the interface, they form a separate persistent long-lasting layer containing a complex thin-film structure that does not mix with the bulk oil. In contrast, thin oil films do not form around a descending water droplet after it crosses the interface.