Oil Microdroplets Research Articles

Surface Cleaning of Oil Contaminants Using Bulk Nanobubbles.

The removal of oil from solid surfaces, such as textiles and plates, remains a challenge due to the strong binding affinity of the oil. Conventional methods for surface cleaning often require surfactants and mechanical abrasion to enhance the cleaning process. However, in excess, these can pose adverse effects on the environment and to the material. This study investigated how bulk nanobubble water can clean oil microdroplets deposited on surfaces like glass coverslips and dishes. Microscopy imaging and further image analysis clearly revealed that these microdroplets detached from both hydrophobic and hydrophilic surfaces when washed with bulk nanobubble water within a fluidic microchannel. Oil contaminant cleaning was also conducted in water as mobile phase to mimic the circumstances that occur in a dishwasher and washing machine. Cleaning on a larger scale also proved very successful in the removal of oil from a porcelain bowl. These results indicate that nanobubble water can easily remove oil contaminants from glass and porcelain surfaces without the assistance of surfactants. This is in stark contrast to negligible results obtained with a control solution without nanobubbles. This study indicates that nanobubble technology is an innovative, low-cost, eco-friendly approach for oil removal, demonstrating its potential for broad practical applications.

Deformable microlaser force sensing

Mechanical forces are key regulators of cellular behavior and function, affecting many fundamental biological processes such as cell migration, embryogenesis, immunological responses, and pathological states. Specialized force sensors and imaging techniques have been developed to quantify these otherwise invisible forces in single cells and in vivo. However, current techniques rely heavily on high-resolution microscopy and do not allow interrogation of optically dense tissue, reducing their application to 2D cell cultures and highly transparent biological tissue. Here, we introduce DEFORM, deformable microlaser force sensing, a spectroscopic technique that detects sub-nanonewton forces with unprecedented spatio-temporal resolution. DEFORM is based on the spectral analysis of laser emission from dye-doped oil microdroplets and uses the force-induced lifting of laser mode degeneracy in these droplets to detect nanometer deformations. Following validation by atomic force microscopy and development of a model that links changes in laser spectrum to applied force, DEFORM is used to measure forces in 3D and at depths of hundreds of microns within tumor spheroids and late-stage Drosophila larva. We furthermore show continuous force sensing with single-cell spatial and millisecond temporal resolution, thus paving the way for non-invasive studies of biomechanical forces in advanced stages of embryogenesis, tissue remodeling, and tumor invasion.

Shaping a Surface Microdroplet by Marangoni Forces along a Moving Contact Line of Four Immiscible Phases

AbstractThe ability to transfer microdroplets between fluid phases offers numerous advantages in various fields. This study focuses on the stability and morphology of a sessile oil microdropletduring the transfer from underwater to air. A distinct transition in microdroplet dynamics is observed, characterized by a shift from a scenario dominated by Marangoni forces to one dominated by capillary forces. In the former regime, the oil microdroplets spread in response to the contact between the water‐air interface and the water‐oil interface. The spreading distance follows a power law relationship of t3/4, reflecting the balance between Marangoni forces and viscous forces. On the other hand, in the capillarity‐dominated regime, the oil microdroplets remain stable at the contact line and after being transferred into the air. The crossover between these two regimes is identified in the parameter space defined by three factors: the approaching velocity of the solid‐water‐air contact line (vcl), the radius of the oil microdroplet (ro), and the radius of the water drop (rw). Furthermore, how to use the four‐phase contact line for shaping oil microdroplets is demonstrated using a full liquid process by the contact line lithography.

Micropatterning of biologically derived surfaces with functional clay nanotubes

ABSTRACT Micropatterning of biological surfaces performed via assembly of nano-blocks is an efficient design method for functional materials with complex organic–inorganic architecture. Halloysite clay nanotubes with high aspect ratios and empty lumens have attracted widespread interest for aligned biocompatible composite production. Here, we give our vision of advances in interfacial self-assembly techniques for these natural nanotubes. Highly ordered micropatterns of halloysite, such as coffee rings, regular strips, and concentric circles, can be obtained through high-temperature evaporation-induced self-assembly in a confined space and shear-force brush-induced orientation. Assembly of these clay nanotubes on biological surfaces, including the coating of human or animal hair, wool, and cotton, was generalized with the indication of common features. Halloysite-coated microfibers promise new approaches in cotton and hair dyeing, medical hemostasis, and flame-retardant tissue applications. An interfacial halloysite assembly on oil microdroplets (Pickering emulsion) and its core–shell structure (functionalization with quantum dots) was described in comparison with microfiber nanoclay coatings. In addition to being abundantly available in nature, halloysite is also biosafe, which makes its spontaneous surface micropatterning prospective for high-performance materials, and it is a promising technique with potential for an industrial scale-up.

Oil droplet fouling on lesser sandeel (Ammodytes marinus) eggshells does not enhance the crude oil induced developmental toxicity

The oil industry's expansion and increased operational activity at older installations, along with their demolition, contribute to rising cumulative pollution and a heightened risk of accidental oil spills. The lesser sandeel (Ammodytes marinus) is a keystone prey species in the North Sea and coastal systems. Their eggs adhere to the seabed substrate making them particularly vulnerable to oil exposure during embryonic development. We evaluated the sensitivity of sandeel embryos to crude oil in a laboratory by exposing them to dispersed oil at concentrations of 0, 15, 50, and 150 µg/L oil between 2 and 16 days post-fertilization. We assessed water and tissue concentrations of THC and tPAH, cyp1a expression, lipid distribution in the eyes, head and trunk, and morphological and functional deformities. Oil droplets accumulated on the eggshell in all oil treatment groups, to which the embryo responded by a dose-dependent rise in cyp1a expression. The oil exposure led to only minor sublethal deformities in the upper jaw and otic vesicle. The findings suggest that lesser sandeel embryos are resilient to crude oil exposure. The lowest observed effect level documented in this study was 36 µg THC/L and 3 µg tPAH/L. The inclusion of these species-specific data in risk assessment models will enhance the precision of risk evaluations for the North Atlantic ecosystems.

High efficiency of biosurfactants in stabilizing oil micro-droplets within the aging time scale of milliseconds: a microfluidic study.

Rapid adsorption of surfactants onto a freshly formed interface is vital for emulsification because emulsification is a competitive process occurring between the very short time span of interface formation and surfactant mass transport. The biosurfactant surfactin has been previously reported to reach adsorption equilibrium at the hydrophobic/hydrophilic interface within hundreds of milliseconds and rapidly reduce the interfacial tension compared to chemically synthesized surfactants. According to a prior study, surfactin is expected to exhibit good performance in stabilizing micro-droplets of oil within the aging time scale of milliseconds. Herein, the stabilities of micro-droplets of n-hexadecane in the presence of a biosurfactant, surfactin (C15-SFT), and a chemically synthesized surfactant, sodium cetyl benzene sulfonate (8-SCBS), were investigated using a microfluidic method. The coalescence frequency of micro-droplets, the evolution of micro-droplet size, and the coalescence time of micro-droplets were evaluated. The results indicated that C15-SFT exhibited superiority over 8-SCBS in stabilizing the micro-droplets of n-hexadecane. Biosurfactant C15-SFT effectively reduced the fusion probability between oil droplets and elongated the coalescence time compared to 8-SCBS, and these phenomena were obvious at a shorter aging time (150 ms) and lower surfactant concentration (0.1 × critical micelle concentration). The stabilities of micro-droplets increased with aging time and the bulk concentration of surfactants. Stable micro-droplets of n-hexadecane were formed in 1 × 10-4 mol L-1 C15-SFT solution at 600 ms aging time, and the bulk concentration was 1 × 10-3 mol L-1 in the case of 8-SCBS. The micro-droplets rarely coalesced in the presence of 1 × 10-4 mol L-1 C15-SFT after 600 ms aging time, but the micro-droplets in 1 × 10-4 mol L-1 8-SCBS coalesced frequently in the midstream and downstream of the coalescence chamber, and big droplets were dominant in the emulsion. The coalescence time of micro-droplets stabilized by C15-SFT was obviously longer than that of those stabilized by 8-SCBS under the same condition, indicating that the interfacial film formed by C15-SFT has much strength to resist coalescence during collisions. This work is helpful for understanding the activity of lipopeptides in the very short early stage of the emulsification process, laying the foundation for biosurfactant research in the fields of enhanced oil recovery, bioremediation of contaminated water or soil, etc.

Do oil droplets and chemical dispersants contribute to uptake of oil compounds and toxicity of crude oil dispersions in cold-water copepods?

ABSTRACT Accidental crude oil spills to the marine environment cause dispersion of oil into the water column through the actions of breaking waves, a process that can be facilitated using chemical dispersants. Oil dispersions contain dispersed micron-sized oil droplets and dissolved oil components, and the toxicity of oil dispersions has been assumed to be associated primarily with the latter. However, most hydrophobic, bioaccumulative and toxic crude oil components are retained within the droplets which may interact with marine filter-feeders. We here summarize the findings of 15 years of research using a unique methodology to generate controlled concentrations and droplet size distributions of dispersed crude oil to study effects on the filter-feeding cold-water copepod Calanus finmarchicus. We focus primarily on the contribution of chemical dispersants and micron-sized oil droplets to uptake and toxicity of oil compounds. Oil dispersion exposures cause PAH uptake and oil droplet accumulation on copepod body surfaces and inside their gastrointestinal tract, and exposures to high exposure (mg/L range) reduce feeding activity, causes reproductive impairments and mortality. These effects were slightly higher in the presence of chemical dispersants, possibly due to higher filtration of chemically dispersed droplets. For C. finmarchicus, dispersions containing oil droplets caused more severe toxic effects than filtered dispersions, thus, oil droplets contribute to the observed toxicity. The methodology for generating crude oil dispersion is a valuable tool to isolate impacts of crude oil microdroplets and can facilitate future research on oil dispersion toxicity and produce data to improve oil spill models.

Efficient Collection of Oil Microdroplets by Hyperbranched, Space‐Filling Open Microfluidic Channels

AbstractOpen microfluidic channels, which capture and transport liquid on flat substrate surfaces through wettability contrast, offer a promising platform for the analysis, mixing, separation, etc. of small‐volume liquid samples. This study focuses on the development of open microfluidic channels featuring oleophilic/oleophobic micropatterning in a hyperbranched, space‐filling structure, thereby creating high‐density channels. These newly designed channels allow for the swift collection of microdroplets with low surface tension within less than 10 s through hierarchical transport and merging of the microdroplets within the channel. The collection efficiency reaches 66% in the channel with the optimized channel geometry. These results underscore the effectiveness of this method for the collection of low surface tension microdroplets, paving the way for the advancement in the domain of open microfluidics of oil, a field that has yet to be fully explored.

Vat photopolymerization 3D printing of oil filled cyanate ester for one-step fabricating self-lubricating parts

High-performance polymers incorporating liquid lubricants can be exploited to fabricate sundry solid-liquid composites for self-lubricating parts in the frontier industries, while the limitations of traditional polymer processing methods generally result in shortcomings including the complex manufacturing process, high cost, and/or low comprehensive properties. In this paper, combining with the unique characteristics of vat photopolymerization three-dimensional (3D) printing, a novel strategy for one-step fabricating self-lubricating parts with microdroplets of oil filled in polymer, namely the vat photopolymerization 3D printing of microemulsion (microemulsion-3DP), is proposed, which realizes the incorporation of oil-droplets into the cyanate ester in a solo step. The self-lubricating properties investigated by friction tests reveal that the average coefficient of friction (COF) of the 3D printed cyanate eater with the lubricant PAO-40 one-step incorporated is decreased to ca. 0.069 from ca. 0.404 of the one without lubricant, 10 times folded nearly. As demonstrated, this innovative method of microemulsion-3DP readily achieves various self-lubricating parts, indicating the promising feasibility of fabricating parts with structures that are difficult to manufacture with traditional processing methods, which will enable a wide range of applications in aerospace, automobile manufacturing, and other cutting-edge fields.

A scalable method toward robust underwater superoleophobic surfaces with microstructure arrays on 304 stainless steel substrates

Underwater superoleophobic surfaces have huge application prospects due to their multiple functions such as antifouling, self-cleaning, manipulation of oil microdroplets, and oil − water separation. However, efficient and low-damage methods for the scalable fabrication of robust underwater superoleophobic surfaces on stainless steel substrates are still lacking. Here, a maskless electrochemical machining technology was developed to fabricate robust underwater superoleophobic surfaces on 304 stainless steel substrates. The square micro pit array was obtained on the surface, and the surface showed excellent superoleophobicity with a contact angle of 154.93 ± 1.42° when submerged in water. In addition, the fabricated underwater superoleophobic surface with the square micro pit array showed good chemical stability, mechanical stability, and anti-friction performance. The friction coefficient of the fabricated underwater superoleophobic surface was 0.0748, which was 60.7% lower than the friction coefficient of a smooth surface. Compared with traditional methods, the proposed technology will promote the practical applications of underwater superoleophobic surfaces in complex underwater environments.

Supercharged Protein Nanosheets for Cell Expansion on Bioemulsions.

Cell culture at liquid-liquid interfaces, for example, at the surface of oil microdroplets, is an attractive strategy to scale up adherent cell manufacturing while replacing the use of microplastics. Such a process requires the adhesion of cells at interfaces stabilized and reinforced by protein nanosheets displaying not only high elasticity but also presenting cell adhesive ligands able to bind integrin receptors. In this report, supercharged albumins are found to form strong elastic protein nanosheets when co-assembling with the co-surfactant pentafluorobenzoyl chloride (PFBC) and mediate extracellular matrix (ECM) protein adsorption and cell adhesion. The interfacial mechanical properties and elasticity of supercharged nanosheets are characterized by interfacial rheology, and behaviors are compared to those of native bovine serum albumin, human serum albumin, and α-lactalbumin. The impact of PFBC on such assembly is investigated. ECM protein adsorption to resulting supercharged nanosheets is then quantified via surface plasmon resonance and fluorescence microscopy, demonstrating that the dual role supercharged albumins are proposed to play as scaffold protein structuring liquid-liquid interfaces and substrates for the capture of ECM molecules. Finally, the adhesion and proliferation of primary human epidermal stem cells are investigated, at pinned droplets, as well as on bioemulsions stabilized by corresponding supercharged nanosheets. This study demonstrates the potential of supercharged proteins for the engineering of biointerfaces for stem cell manufacturing and draws structure-property relationships that will guide further engineering of associated systems.

Carbon dot-based superhydrophobic modification of a covalent organic framework for oil-in-water emulsion separation.

A super hydrophobic composite is developed for the first time through the non-covalent self-assembly of a hydrophilic covalent organic framework (COF) and amphoteric CDs to achieve highly selective separation of dispersed micro droplets of oil from an oil/water mixture.

Surfactant-stabilized oil microdroplets extraction from oily wastewater

Surfactant-stabilized oil microdroplets extraction from oily wastewater

Inkjet-Assisted Electroformation of Magnetically Guidable Water Striders for Interfacial Microfluidic Manipulation.

Gerridae, colloquially called water striders, are a peculiar class of insects characterized by the extraordinary ability to walk on the surface of water bodies. Owing to this capacity, they constitute an ideal source of inspiration for designing untethered microdevices capable of navigating the interface between two fluids. Such steerable micrometric objects can be of great interest for various applications, ranging from the handling of floating objects to the remote control of microreactions and the manipulation of self-assembled monolayers. This paper describes the realization of artificial water striders via an inkjet-assisted electroforming approach. Inkjet deposition patterns the negative mask, which is subsequently filled with different layers of metals through electroforming. One of such layers is the magnetic alloy NiFe, which allows wireless propulsion of the striders by means of externally applied magnetic fields. The magnetic actuation tests prove good maneuverability at the water-air and silicone oil-air interfaces, with superior control over the speed and position of the devices. The surface of the devices is modified to tune its superficial energy in order to maximize buoyancy on these different combinations of fluids. A magnetic field-controlled strider manipulates a droplet and demonstrates collecting oil microdroplets and synthesizing platinum nanoparticles by chemical microreactions. Finally, the remotely operated microrobot could be employed in laboratories as a real avatar of chemists.

Photo-Phytotherapeutic Gel Composed of Copaifera reticulata, Chlorophylls, and k-Carrageenan: A New Perspective for Topical Healing.

Chronic wound healing represents an impactful financial burden on healthcare systems. In this context, the use of natural products as an alternative therapy reduces costs and maintains effectiveness. Phytotherapeutic gels applied in photodynamic therapy (PDT) have been developed to act as topical healing medicines and antibiotics. The bioactive system is composed of Spirulina sp. (source of chlorophylls) and Copaifera reticulata oil microdroplets, both incorporated into a polymeric blend constituted by kappa-carrageenan (k-car) and F127 copolymer, constituting a system in which all components are bioactive agents. The flow behavior and viscoelasticity of the formulations were investigated. The photodynamic activity was accessed from studies of the inactivation of Staphylococcus aureus bacteria, the main pathogen of hospital relevance. Furthermore, in vivo studies were conducted using eighteen rabbits with dermatitis (grade III and IV) in both paws. The gels showed significant antibiotic potential in vitro, eliminating up to 100% of S. aureus colonies in the presence or absence of light. The k-car reduced 41% of the viable cells; however, its benefits were enhanced by adding chlorophyll and copaiba oil. The animals treated with the phytotherapeutic medicine showed a reduction in lesion size, with healing and re-epithelialization verified in the histological analyses. The animals submitted to PDT displayed noticeable improvement, indicating this therapy's viability for ulcerative and infected wounds. This behavior was not observed in the iodine control treatment, which worsened the animals' condition. Therefore, gel formulations were a viable alternative for future pharmaceutical applications, aiming at topical healing.

The Combined Effects of the Membrane and Flow Channel Development on the Performance and Energy Footprint of Oil/Water Emulsion Filtration.

Membrane filtration is a promising technology for oil/water emulsion filtration due to its excellent removal efficiency of microdroplets of oil in water. However, its performance is highly limited due to the fouling-prone nature of oil droplets on hydrophobic membranes. Membrane filtration typically suffers from a low flux and high pumping energy. This study reports a combined approach to tackling the membrane fouling challenge in oil/water emulsion filtration via a membrane and a flow channel development. Two polysulfone (PSF)-based lab-made membranes, namely PSF- PSF-Nonsolvent induced phase separation (NIPS) and PSF-Vapor-induced phase separation (VIPS), were selected, and the flow channel was modified into a wavy path. They were assessed for the filtration of a synthetic oil/water emulsion. The results showed that the combined membrane and flow channel developments enhanced the clean water permeability with a combined increment of 105%, of which 34% was attributed to the increased effective filtration area due to the wavy flow channel. When evaluated for the filtration of an oil/water emulsion, a 355% permeability increment was achieved from 43 for the PSF-NIPS in the straight flow channel to 198 L m-2 h-1 bar-1 for the PSF-VIPS in the wavy flow channel. This remarkable performance increment was achieved thanks to the antifouling attribute of the developed membrane and enhanced local mixing by the wavy flow channel to limit the membrane fouling. The increase in the filtration performance was translated into up to 78.4% (0.00133 vs. 0.00615 kWh m-3) lower in pumping energy. The overall findings demonstrate a significant improvement by adopting multi-pronged approaches in tackling the challenge of membrane fouling for oil/water emulsion filtration, suggesting the potential of this approach to be applied for other feeds.

Performance and mechanism study on surfactant-stabilized oil microdroplets extraction from oily wastewater

Petrochemical, coal chemical, and metal smelting industries generate substantial amounts of oily wastewater. The major obstacle in treating these wastewaters is surfactant-stabilized oil microdroplets. Solvent extraction has shown significant application potential in this kind of oil microdroplet removal due to its high-efficiency, economy, and environmental friendliness. However, mechanistic study and other in-depth investigation are still needed to support the more high-performance extractant screening and process design. In this study, in terms of the surfactant-stabilized oil microdroplet extraction from oily wastewater, the mechanism was analyzed by characterizing the compositions and properties of the intermediate layer and extractant phase. It was demonstrated that, unlike conventional liquid–liquid extraction system containing molecular solutes, the extraction of surfactant-stabilized oil microdroplets is accomplished by the mass transfer of extractant from the exterior to the interior of the oil microdroplets and the rise of extractant-containing oil droplets in the aqueous phase with critical influences. This behavior of mass transfer and droplet rise is supported by the mechanism of the emulsion liquid membrane extraction technique and the Stokes’ law. In addition, we illustrated the positive or negative effects of several factors (e.g. molecular extractant type, extractant dosage, stirring time, stirring speed and so on) on extraction efficiency. This confirmed the mechanism proposed above. And multistage extraction experiments showed that this solvent extraction technology was able to treat oily wastewater to discharge standards. Finally, by combining with the feasibility analysis of extractant regeneration, non-polar extractants were considered as the more suitable extractant than polar extractant because of the realizability of regeneration, lower costs for regeneration and better extraction performance.

Partial substitution of conventional synthetic surfactant by biosurfactant enhances the stability of micro-droplets of crude oil in surfactant solution in flow state and within sub-second period

Microbial lipopeptides have been proposed to adsorb at interface rapidly and have synergistic effect with synthetic surfactant, and we assumed that stable droplets of oil would generate and oil-in-water emulsion with good stability would be obtained using the mixture of microbial lipopeptides and synthetic surfactant in short time scale. Here, the interfacial properties of the mixture of microbial lipopeptide and petroleum sulphonates has been evaluated using the coalescence frequency of the micro-droplets of crude oil in surfactant solutions in flow state and within sub-second period based on a microfluidic method. Results showed that partial substitution of petroleum sulphonates by lipopeptide enhanced the stability of micro-droplets of crude oil in surfactant solutions. To form stable micro-droplets of crude oil, less lipopeptide/petroleum sulphonates mixture (m:m=1:1) was needed than petroleum sulphonates. Moreover, higher salt tolerance, less demand of alkali, and shorter adsorption time were obtained for lipopeptide/petroleum sulphonates mixture to form stable emulsion comparing with that of individual petroleum sulphonates mixture. The present study provide novel information of lipopeptide/petroleum sulphonates mixture in generating stable crude oil-in-water emulsion at flow state.

Evaporation Dynamics of Sessile Saline Microdroplets in Oil.

The occurrence of concentration and temperature gradients in saline microdroplets evaporating directly in air makes them unsuitable for nucleation studies where homogeneous composition is required. This can be addressed by immersing the droplet in oil under regulated humidity and reducing the volume to the picoliter range. However, the evaporation dynamics of such a system is not well understood. In this work, we present evaporation models applicable for arrays of sessile microdroplets with dissolved solute submerged in a thin layer of oil. Our model accounts for the variable diffusion distance due to the presence of the oil film separating the droplet and air, the variation of the solution density and water activity due to the evolving solute concentration, and the diffusive interaction between neighboring droplets. Our model shows excellent agreement with experimental data for both pure water and NaCl solution. With this model, we demonstrate that assuming a constant evaporation rate and neglecting the diffusive interactions can lead to severe inaccuracies in the measurement of droplet concentration, particularly during nucleation experiments. Given the significance of droplet evaporation in a wide array of scientific and industrial applications, the models and insights presented herein would be of great value to many fields of interest.

Characterization of the Dissolution of Water Microdroplets in Oil

Water in oil emulsions have a wide range of applications from chemical technology to microfluidics, where the stability of water droplets is of paramount importance. Here, using an accessible and easily reproducible experimental setup we describe and characterize the dissolution of water in oil, which renders nanoliter-sized droplets unstable, resulting in their shrinkage and disappearance in a time scale of hours. This process has applicability in creating miniature reactors for crystallization. We test multiple oils and their combinations with surfactants exhibiting widely different rates of dissolution. We derived simple analytical equations to determine the product of the diffusion coefficient and the relative saturation density of water in oil from the measured dissolution data. By measuring the moisture content of mineral and silicone oils with Karl Fischer titration before and after saturating them with water, we calculated the diffusion coefficient of water in these two oils.