Oil Microdroplets Research Articles

Microfluidic approach to produce emulsion-filled alginate microgels

Carrying lipophilic compounds protection within alginate microgels is a challenge, mainly due to the necessary oil-core matrix. Based on this demand, this study aimed to evaluate the use of glass microfluidic devices to produce emulsion-filled alginate microgels and understand the effect of process variables on microgels size and polydispersity. Firstly, stable and monodisperse size-distributed oil microdroplets were formed by preparing an oil-in-water (O/W) emulsion using high shear followed by ultrasound. The continuous aqueous phase was composed of Na-alginate, cellulose nanocrystals and ultrafine calcium carbonate. Sunflower oil composed the emulsion oil phase (10%, w/w). Secondly, oil-in-water-in-oil (O/W/O) emulsions were formed within microfluidics devices to obtain emulsion-filled hydrogel particles. The previously produced O/W emulsion was introduced as the dispersed phase into a continuous phase containing sunflower oil, PGPR and acetic acid. The aqueous phase was gelled by internal gelation, promoting the alginate network. Monodisperse particle size distribution was observed, with a coefficient of variation lower than 6% and mean size ranging from 259 to 526 μm. Microgels size was influenced by the viscosity of O/W emulsion and the phases flow rates. Our results show the potential of microfluidic processes for producing microgels and filled microgels to encapsulate lipophilic compounds.

Electrochemical characterization of individual oil micro-droplets by high-frequency nanocapacitor array imaging.

CMOS-based nanocapacitor arrays allow local probing of the impedance of an electrolyte in real time and with sub-micron spatial resolution. Here we report on the physico-chemical characterization of individual microdroplets of oil in a continuous water phase using this new tool. We monitor the sedimentation and wetting dynamics of individual droplets, estimate their volume and infer their composition based on their dielectric constant. From measurements before and after wetting of the surface, we also attempt to estimate the contact angle of individual micron-sized droplets. These measurements illustrate the capabilities and versatility of nanocapacitor array technology.

The impact of exposure timing on embryo mortality and the partitioning of PAHs when cod eggs are exposed to dispersed and dissolved crude oil

During sub-sea oil spills to the marine environment, oil droplets will rise towards the sea surface at a rate determined by their density and diameter as well as the vertical turbulence in the water. Micro-droplets (< 50 µm) are expected to have prolonged residence times in the water column. If present, pelagic fish eggs may thus be exposed to dispersed oil from subsurface oil spills for days, and the contribution of these micro-droplets to toxicity is not well known. The purpose of this work was to investigate to what extent timing of exposure and the presence of oil micro droplets affects PAH uptake and survival of pelagic Atlantic cod eggs. A single batch of eggs was separated in two groups and exposed to dispersions and corresponding water-soluble fraction at 3–7 days (Early exposure) and 9–13 days (Late exposure) post fertilization. Partitioning of PAHs between crude oil microdroplets, water and eggs was estimated as well as the contribution of oil droplets to PAH body residue and acute and delayed mortality. Timing of oil exposure clearly affects both the mortality rate and the timing of mortality. Even though the body residue of PAHs were lower when embryos were exposed in the later embryonic stage, mortality rate increased relative to the early exposure indicating that critical body residue threshold is stage specific. Although our results suggest that the dissolved fraction is the dominating driver for toxicity in cod embryos exposed to oil dispersions, crude oil micro droplets contribute to increased mortality as well.

Micro-dispersed essential oils loaded gelatin hydrogels with antibacterial activity

Plant-based essential oils (EOs) are natural antimicrobial agents that have a relatively new application as edible coatings to extend the shelf life of foods such as meat. In this study, we developed gelatin hydrogels containing microdroplets of rosemary essential oil (REO) and orange essential oil (OEO). The microdroplets were successfully stabilized by the surfactant Tween®80. The droplet size distribution was slightly affected by the type of EO and homogenization time. The rheological properties in the linear viscoelastic range depend on the EO concentration and the Bloom number of the gelatin. The nonlinear behavior remains typical of gelatin gels, with stiffening and shear thickening at large deformation amplitudes. Escherichia coli and Bacillus cereus were sensitive to the gelatin-REO hydrogels with a minimum inhibitory concentration (MIC) of 0.5%. The gelatin-OEO hydrogels inhibited only Bacillus cereus with an MIC of 0.5%, but the gelatin-REO hydrogels showed greater cell reduction. Surprisingly, the Staphylococcus aureus strain used here was resistant to all gelatin-EO hydrogels. Our experiments show that gelatin-EO hydrogels prepared by simple emulsification have high stability and antibacterial activity suitable for potential preservation of gelatin-tolerant foods.

Supercritical CO2 assisted construction of carbon black/polypropylene composite foams with bioinspired open-cell micro-nano hierarchical structure and outstanding performance for oil/water separation

A novel composite foam material with bioinspired open-cell micro-nano hierarchical structure was facilely fabricated by incorporating nano carbon black (CB) into polypropylene (PP) under supercritical CO2 condition. The results demonstrated that when the amount of CB was 10 wt%, the enhancement of thermal conductivity greatly enhanced the heterogeneous nucleation process and promoted the appearance of a large number of open-cell structures. The fabricated PP/CB foams were confirmed to have highly open-cell structure with huge numbers of nano-cavities spread over the cell wall, forming a unique micro-nano hierarchical structure. Three kinds of commonly used oils have been tested, demonstrating with a maximum adsorption efficiency of 22.6 g/g for diesel oil. Furthermore, over broad pH conditions, the PP/CB10 foam rapidly adsorbed oil microdroplets with 95% removal efficiency. Thus, this obtained composite foam would advance the development of multifunctional open-cell foam materials for highly efficient oil/water separation application over broad pH condition.

Enhanced Water Nucleation and Growth Based on Microdroplet Mobility on Lubricant-Infused Surfaces.

Lubricant-infused surfaces (LISs) can promote stable dropwise condensation and improve heat transfer rates due to a low nucleation free-energy barrier and high droplet mobility. Recent studies showed that oil menisci surrounding condensate microdroplets form distinct oil-rich and oil-poor regions. These topographical differences in the oil surface cause water microdroplets to rigorously self-propel long distances, continuously redistributing the oil film and potentially refreshing the surface for re-nucleation. However, the dynamic interplay between oil film redistribution, microdroplet self-propulsion, and droplet nucleation and growth is not yet understood. Using high-speed microscopy, we reveal that during water condensation on LISs, the smallest visible droplets (diameter: ∼1 μm, qualitatively representing nucleation) predominantly emerge in oil-poor regions due to a lower nucleation free-energy barrier. Considering the significant heat transfer performance of microdroplets (<10 μm) and transient characteristic of microdroplet movement, we compare the apparent nucleation rate density and water collection rate for LISs with oils of different viscosities and a solid hydrophobic surface at a wide range of subcooling temperatures. Generally, the lowest lubricant viscosity leads to the highest nucleation rate density. We characterize the length and frequency of microdroplet movement and attribute the nucleation enhancement primarily to higher droplet mobility and surface refreshing frequency. Interestingly and unexpectedly, hydrophobic surfaces outperform high-viscosity LISs at high subcooling temperatures but are generally inferior to any of the tested LISs at low temperature differences. To explain the observed nonlinearity between LISs and the solid hydrophobic surface, we introduce two dominant regimes that influence the condensation efficiency: mobility-limited and coalescence-limited. We compare these regimes based on droplet growth rates and water collection rates on the different surfaces. Our findings advance the understanding of dynamic water-lubricant interactions and provide new design rationales for choosing surfaces for enhanced dropwise condensation and water collection efficiencies.

Lubricant self-replenishing slippery surface with prolonged service life for fog harvesting

Slippery lubricant-infused surfaces exhibit excellent fog-harvesting capacities compared with superhydrophobic and superhydrophilic surfaces. However, lubricant depletion is typically unavoidable under dynamic conditions, and reinfused oil is generally needed to recover the fog-harvesting capacity. Herein, an effective strategy for delaying the depletion of lubricant to prolong the service life of fog harvesting is proposed. An ultrathin transparent lubricant self-replenishing slippery surface was fabricated via facile one-step solvent evaporation polymerization. The gel film of the lubricant self-replenishing slippery surface, which was embedded with oil microdroplets, was attached to glass slides via the phase separation and evaporation of tetrahydrofuran. The gel film GFs-150 (with oil content 150 wt% of aminopropyl-terminated polydimethyl siloxane (PDMS-NH2)) exhibited superior slippery and fog-harvesting performance to other gel films. Furthermore, the slippery surfaces with the trait of oil secretion triggered by mechanical stress exhibited better fog-harvesting capabilities and longer service life than surfaces without the function of lubricant self-replenishment. The lubricant self-replenishing, ultrathin, and transparent slippery surfaces reported herein have considerable potential for applications involving narrow spaces, visualization, long service life, etc.

P–268 Assessing the effect of media, oil and culture dishes on media osmolality and its dynamics in the culture system

Abstract Study question Can lab-related variables (media type, oil viscosity, microdroplet volume and culture dish design) modulate media evaporation and improve its stability during culture? Summary answer Using dishes with pre-defined wells, big volume microdroplets and high-viscosity mineral oil can help to reduce media evaporation and improve osmolality stability during embryo culture. What is known already Osmolality measures the number of solute particles present in a solution and is an important variable of a human embryo culture system. High ambient temperature and low humidity may induce evaporation in culture media, increasing its osmolality. In addition, recent tendencies in IVF laboratories, such as extending the embryo culture uninterruptedly until day 6/7 or the use of dry benchtop incubators, may intensify evaporation. Surpassing a 300mOsm/kg threshold can result deleterious for embryo development and impair clinical results. Different strategies (e.g. oil type/volume, dish type, micro-drop volume) have been proposed to reduce evaporation and stabilize osmolality during culture. Study design, size, duration Four variables were analyzed in their capacity to reduce media evaporation: type of culture medium, micro-droplet volume, oil viscosity and type of culture dish. Dishes were prepared with 5ml of oil and 50µl microdroplets (25µl were used for the comparison of micro-droplet volumes). Dishes were cultured in parallel in a dry benchtop incubator (AD–3100, Astec), and osmolality measured daily for seven days with a freezing point depression osmometer (Osmo1®, Advanced Instruments, accuracy ≤2mOsm/kg). Participants/materials, setting, methods The following comparison groups were analyzed: 1) Seven commercial single-step media with three differing initial osmolalities (approximately 260, 280 and &amp;gt;290mOsm/kg); 2) oil with high, medium or low viscosity; 3) 50 vs. 25µl microdroplets; 4) 35mm flat Petri dish vs. 35mm dish with defined wells. Temperature in the incubator was monitored continuously (T+Button, BrightSentinel), as well as room temperature and humidity (Octax Log&amp;Guard, Vitrolife). All were stable at 37.3±0.05oC, 22.1±0.6 oC and 67.4±7.4%, respectively. Main results and the role of chance Evaporation occurred in all the studied groups, but its rate was modulated by various parameters. Culture dishes designed with pre-defined wells reduced evaporation when compared to regular Petri dishes (Increase 11.3mOsm/kg and increase 12.5mOsm/kg, respectively from day 0 to 7 (P = 0.007)). Similarly, oil viscosity had an impact in osmolality stability during culture, with an increase of 14.7mOsm/kg, 16.3mOsm/kg and 19.2mOsm/kg observed when using mineral oil with high, medium and low viscosity, respectively (P = 0.009). Finally, reducing the volume of the medium microdroplets from 50 to 25µl derived in higher evaporation rates, but without significant differences (Increase 14.7mOsm/kg and increase 15.8mOsm/kg, respectively (P = 0.325)). Different evaporation rates were observed between the seven studied culture media attending their three-differing initial osmolalities. Significant differences were observed for a media respect another three media with differing initial osmolality (P = 0.001, P = 0.01 and P = 0.015). Their initial osmolality had a direct correlation with the maximum osmolality reached at the end of culture. Thus, media with a high initial osmolality (&amp;gt;290mOsm/kg) resulted in hyperosmotic media above the recommended 300mOsm/kg threshold by the end of culture and, by contrast, the studied media with lower initial values were able to maintain osmolality below 300mOsm/kg for the whole duration of the culture. Limitations, reasons for caution While a clear effect was observed by the studied variables, other parameters, such as oil volume or dish preparation techniques, could also play a role in osmolality maintenance and could be studied in the future. Additionally, these findings could vary between different centers and should be validated in each laboratory. Wider implications of the findings: Osmolality has been shown to have a direct impact on embryo development, embryo quality and clinical outcomes. Carefully defining the consumables and methodologies used in the IVF laboratory will improve the stability of the culture system and, consequently, reduce the stress imparted to the embryos and gametes under culture. Trial registration number Not applicable

Dissolution of microdroplets in a sparsely miscible liquid confined by leaky walls

Abstract

Ouzo Column under Impact: Formation of Emulsion Jet and Oil-Lubricated Droplet.

We investigated the dynamics of a liquid column consisting of ouzo emulsion under the impact generated when the liquid container lands on a hard ground. At a cavitation number of 0.36, where cavitation is expected to occur, our high-speed videography captured the traveling jet and cavitation bubbles while the oil microdroplets in ouzo after different runs of impact were visualized by an optical microscope. Importantly, the impact on an ouzo column can eject a focused jet of the emulsion and deposit a small volume of emulsion on a solid substrate. As revealed by our still photography, the deposited emulsion formed an oil-lubricated drop immediately. Our findings have implications for jetting applications such as inkjet printing of emulsions or fast deposition of self-lubricating drops for assembling supraparticles. We also discuss the jet formation mechanism in terms of the existence of oil microdroplets.

Restricted intramolecular rotation of fluorescent molecular rotors at the periphery of aqueous microdroplets in oil

Fluorescent molecular rotor dyes, including Cy3, Cy5, and Alexa Fluor 555, dissolved in micron-sized aqueous droplets (microdroplets) in oil were excited, and the fluorescence intensity was recorded as function of time. We observed lengthening of the fluorescence lifetime of these dyes at the water–oil periphery, which extended several microns inward. This behavior shows that intramolecular rotation is restricted at and near the microdroplet interface. Lengthened lifetimes were observed in water microdroplets but not in microdroplets composed of organic solvents. This lifetime change was relatively insensitive to added glycerol up to 60%, suggesting that solution viscosity is not the dominant mechanism. These restricted intramolecular rotations at and near the microdroplet periphery are consistent with the reduced entropy observed in chemical reactions in microdroplets compared to the same reaction conditions in bulk solution and helps us further understand why microdroplet chemistry differs so markedly from bulk-phase chemistry.

Spatial localization of charged molecules by salt ions in oil-confined water microdroplets.

Cells contain more than 100 mM salt ions that are typically confined to dimensions of 5 to 10 micrometers by a hydrophobic cellular membrane. We found that in aqueous microdroplets having the same size as cells and that are confined in hydrocarbon oil, negatively charged molecules were distributed rather uniformly over the interior of the microdroplet, whereas positively charged molecules were localized at and near the surface. However, the addition of salt (NaCl) to the microdroplet caused all charged molecules to be localized near the oil-water interface. This salt-induced relocalization required less salt concentration in microdroplets compared to bulk water. Moreover, the localization became more prominent as the size of the microdroplet was reduced. The relocatization also critically depended on the type of oil. Our results imply that salt ions and different hydrophobic interfaces together may govern the local distribution of charged biomolecules in confined intracellular environments.

The Complexity of Spills: The Fate of the Deepwater Horizon Oil.

The Deepwater Horizon oil spill was the largest, longest-lasting, and deepest oil accident to date in US waters. As oil and natural gas jetted from release points at 1,500-m depth in the northern Gulf of Mexico, entrainment of the surrounding ocean water into a buoyant plume, rich in soluble hydrocarbons and dispersed microdroplets of oil, created a deep (1,000-m) intrusion layer. Larger droplets of liquid oil rose to the surface, forming a slick of mostly insoluble, hydrocarbon-type compounds. A variety of physical, chemical, and biological mechanisms helped to transform, remove, and redisperse the oil and gas that was released. Biodegradation removed up to 60% of the oil in the intrusion layer but was less efficient in the surface slick, due to nutrient limitation. Photochemical processes altered up to 50% (by mass) of the floating oil. The surface oil expression changed daily due to wind and currents, whereas the intrusion layer flowed southwestward. A portion of the weathered surface oil stranded along shorelines. Oil from both surface and intrusion layers were deposited onto the seafloor via sinking marine oil snow. The biodegradation rates of stranded or sedimented oil were low, with resuspension and redistribution transiently increasing biodegradation. The subsequent research efforts increased our understanding of the fate of spilled oil immensely, with novel insights focusing on the importance of photooxidation, the microbial communities driving biodegradation, and the formation of marine oil snow that transports oil to the seafloor.

Prospective Study of Silicone Oil Microdroplets in Eyes Receiving Intravitreal Anti-Vascular Endothelial Growth Factor Therapy in 3 Different Syringes

To compare the prevalence of intravitreal silicone oil microdroplets detected by slit-lamp biomicroscopy in eyes with 6 or more injections of the same anti-vascular endothelial growth factor (VEGF) drug. Prospective, cross-sectional case series. A total of 260 consecutive eyes receiving 1 of 3 intravitreal anti-VEGF drugs for choroidal neovascularization, diabetic macular edema, or venous occlusive disease. The control group included 147 fellow eyes with no prior intravitreal injections. The anterior and mid-vitreous were carefully examined using 12× to 16× magnification through dilated pupils with ocular saccades before an injection. Silicone oil microdroplets were graded on a scale from 0 to 4+ based on the number and size of droplets. Presence and severity of silicone oil microdroplets in the vitreous. Silicone oil microdroplets were observed in 78.3% of eyes receiving bevacizumab in Becton Dickinson (BD, Franklin Lakes, NJ) 0.3-mL polypropylene syringes, 14.4% of eyes receiving ranibizumab in 1.0-mL BD polypropylene syringes or more recently glass prefilled syringes, 48.5% of eyes receiving aflibercept in 1.0-mL BD polycarbonate syringes, and 0% of eyes in controls. The differences among the 4 groups were statistically significant at P < 0.001. The severity of silicone oil microdroplets was significantly greater in eyes using BD 0.3-mL polypropylene syringes than BD 1.0-mL polypropylene syringes, BD 1.0-mL polycarbonate syringes, or controls (P < 0.001). The severity of silicone oil microdroplets in eyes using BD 1.0-mL polycarbonate syringes was significantly greater than BD 1.0-mL polypropylene syringes (P= 0.012) and controls (P < 0.001). There was no significant difference between silicone oil microdroplet severity between BD 1.0-mL polypropylene syringes and controls (P= 1.0). The BD 0.3-mL polypropylene syringes with repackaged bevacizumab and the BD 1.0-mL polycarbonate syringes with aflibercept cause a higher likelihood of silicone oil microdroplets. Intravitreal injections in eyes receiving multiple regular anti-VEGF injections should be supplied in silicone-free syringes.

Simulation studies on picolitre volume droplets generation and trapping in T-junction microchannels

In this paper, we present simulation studies on the formation of water microdroplets in mineral oil in a T-junction Microfluidics device. We have studied the droplet generation in two different regimes, viz., squeezing and squeezing to dripping transition regime. The effect of fluid flow rates, and surfactant concentration on the droplet generation has been investigated. It is seen that a rise in the concentration of surfactant by 4%, increases the frequency of droplet generation by 16% at the higher capillary number (Ca = 0.02), whereas, there is only a marginal or no change in the case of squeezing regime (Ca = 0.0028–0.008). We have also studied the trapping of the generated microdroplets in microwells. It is observed that the trapping of the droplet is highly influenced by the viscous drag force, droplet length, the surface energy of the droplet, droplet speed, depth of the Well for trapping and alignment of the two plates constituting the device. Our studies reveal that the droplets travelling faster than a critical trapping velocity do not get trapped in the Well. Addition of a surfactant to the mineral oil is seen to lead to a significant reduction in the critical velocity for the droplet trapping. Trapping of droplets travelling at velocities close to the critical velocity for trapping depends strongly on the alignment of the two plats of the Slip-Chip device.

Porous Gelatin Membranes Obtained from Pickering Emulsions Stabilized with h-BNNS: Application for Polyelectrolyte-Enhanced Ultrafiltration.

In recent years, numerous studies have been conducted to develop biopolymer-based membranes, highlighting the challenges to prepare porous structures with control porosity. In this paper an innovative method that relies on the generation of Pickering emulsions was developed to prepare porous membranes from gelatin for filtration purpose. Hexagonal boron nitride nanosheets (h-BNNS) were used to stabilize micro-droplets of castor oil in a continuous homogeneous gelatin solution. Two steps in the membrane preparation process strongly influenced the porous structure. Specifically, the duration of the drying time after emulsion casting and the duration of the cross-linking step affected membrane pore size, hydrophobicity, water swelling, and water permeability. By controlling these two steps, membranes could be designed with pore size between 0.39 and 1.60 μm and display pure water permeability between 150 and 506 L h−1 m−2 bar−1. These membranes have been tested for complexation–ultrafiltration experiments in which iron ions were removed from aqueous solutions with/without poly (acrylic acid) (PAA). Without PAA, the removal of free iron (II) ions was low (not more than 14%). The addition of PAA (200 ppm) allowed obtaining high removal rates (97%) at pH ≥ 5 with 3 bars of transmembrane pressure.

All-cellulose composite membranes for oil microdroplet collection

Oil spills on ocean waters represent a major threat to marine ecosystems. A significant part of the spilled oil is dispersed in microdroplets that are not recovered by traditional oil-removing methods. In this work, we report on the manufacture of cellulose acetate (CA) electrospun non-woven membranes, stamped with different cellulose nanocrystal (CNC) patterns. We demonstrate the use of the membranes produced as selective oil microdroplets removal from water emulsions with an efficiency up to 80%. Screenprinting was used to imprint different CNC designs on the CA surface membranes. To promote the adhesion between the CNCs and the CNCs with the CA fibers the membrane was subjected to a thermal and chemical treatments. Oil droplets were collected under water in the oleophilic CNC pattern while the water could flow through the hydrophilic CA electrospun non-woven membrane. The application of a non-woven all cellulosic composite membrane for separation of a water/oil suspension is presented. The under-water wetting behavior, of annealed cellulose nanocrystals, for oil is studied. Special consideration is given to the capability for the collection of oil micro droplets in aqueous suspension and the influence of the geometrical pattern of the cellulose nanoparticles layer in oil recovery efficiency.

Bacteria forming drag-increasing streamers on a drop implicates complementary fates of rising deep-sea oil droplets

Competing time scales involved in rapid rising micro-droplets in comparison to substantially slower biodegradation processes at oil-water interfaces highlights a perplexing question: how do biotic processes occur and alter the fates of oil micro-droplets (<500 μm) in the 400 m thick Deepwater Horizon deep-sea plume? For instance, a 200 μm droplet traverses the plume in ~48 h, while known biodegradation processes require weeks to complete. Using a microfluidic platform allowing microcosm observations of a droplet passing through a bacterial suspension at ecologically relevant length and time scales, we discover that within minutes bacteria attach onto an oil droplet and extrude polymeric streamers that rapidly bundle into an elongated aggregate, drastically increasing drag that consequently slows droplet rising velocity. Results provide a key mechanism bridging competing scales and establish a potential pathway to biodegradation and sedimentations as well as substantially alter physical transport of droplets during a deep-sea oil spill with dispersant.

Author Correction: Surface-engineered sponges for recovery of crude oil microdroplets from wastewater

Author Correction: Surface-engineered sponges for recovery of crude oil microdroplets from wastewater

Surface-engineered sponges for recovery of crude oil microdroplets from wastewater

In the United States, the oil industry produces over 15 billion barrels of wastewater contaminated with crude oil microdroplets annually. Current methods are ineffective for the removal of these microdroplets at the variable pH conditions commonly found in wastewater. Here, an innovative surface-engineered sponge (SEnS) that synergistically combines surface chemistry, charge and roughness, provides a solution to this problem. Over broad pH conditions, the SEnS rapidly adsorbed oil microdroplets with 95–99% removal efficiency, predominantly facilitated by Lifshitz–van der Waals forces. At the optimum pH, 92% of the oil was adsorbed within 10 min. The oil was subsequently recovered by solvent extraction under ambient conditions, and the cleaned SEnS was reused for oil microdroplets adsorption ten times. The combined efficacy and reusability can enable large-scale removal and recovery of crude oil microdroplets from wastewater. Current methods to remove oil microdroplets from wastewater are ineffective at the variable pH conditions commonly found in wastewater. This study presents a surface-engineered sponge that synergistically combines surface chemistry, charge and roughness, providing a solution to this problem.