Surfactant-free Emulsions Research Articles

An Anchored Fe-Cu LDH onto a Polyvinylidene Fluoride Membrane with Strong Peroxymonosulfate Activation-Induced Degradation of Methylene Blue and Self-Cleaning Property of Oil/Water Separation.

Developing a strong catalytic antifouling membrane to achieve efficient sewage purification has great potential for alleviating water crisis. In this work, we designed and prepared an Fe/Cu-layered double hydroxide (Fe-Cu LDH)-coated polyvinylidene fluoride (PVDF) composite membrane (PVDF/Fe-Cu LDHs) with strong antifouling and activating peroxymonosulfate (PMS) catalytic degradation performance through polydopamine-coordination anchoring and hydrothermal reaction. The results showed that abundant hydroxyl groups of the LDH surface endowed the superhydrophilicity (water contact angle <10°) and underwater superoleophobicity (underwater-oil contact angle >150°) of the membrane surface, which displayed outstanding resistance to crude oil adhesion. With assistance of the LDH surface-bound sulfate radical of the peroxymonosulfate system, the PVDF/Fe-Cu LDH membrane demonstrated robust catalytic degradation performance for the methylene blue (MB) in the dark; the degradation rate constant (k, min-1) reached 0.96. Meanwhile, facing the oily wastewater, the selective wettability and charge effect of LDH of the surface made the PVDF/Fe-Cu LDH membrane realize the separation for the various surfactant-free and surfactant-stabilized emulsions. Importantly, the PMS-activation catalytic produced the ROS (•SO4-,•OH, •O2-, and 1O2), which enhanced the regeneration of the fouled PVDF/Fe-Cu LDH membrane and obtained a high flux recovery ratio in the dark (94.7%) after 10 cycles of separation experiments. Hence, we believed that the PVDF/Fe-Cu LDH membrane can provide inspiration for the development and further practical application of antifouling membranes.

Engineering surfactant-free pickering double emulsions gels with different structures as low-calorie fat analogues: Tunable oral perception, inhibiting lipid digestion, and potent co-delivery for lycopene and epigallocatechin gallate

Structural design has been as a transformative strategy to create clean-label and well-nourished fat-based foods. Herin, surfactant-free, plant-based oil-in-water-in-oil (O/W/O) and water-in-oil-in-water (W/O/W) emulsions gels (EGs) were designed using protein microgels and fat crystals formed in situ, which achieved dual-interface Pickering stabilization. The suitability and difference of O/W/O and W/O/W EGs as fat analogues in maintaining fat texture, inhibiting lipid digestion, target release and bioactivity of co-loading epigallocatechin gallate (EGCG) and lycopene were examined. O/W/O and W/O/W EGs displayed own unique characteristics, and could be tailored to optimize their performance. O/W/O EGs provided smoother oral perception similar to butter. The multi-structure and interface modulation for double EGs achieved inhibiting lipid digestion, fat phase position mainly controlled the digestive process. Co-delivery systems exhibited synchronous release profiles, allowing a more obvious in-time sustained release of lycopene in O/W/O and EGCG in W/O/W EGs. Both co-delivery O/W/O and W/O/W showed anti-inflammatory bioactivity.

Research on optimizing focused ultrasonic parameters for Surfactant-Free nanoemulsion with prolonged stability

Stable-state emulsions with no phase separation and dispersed-particle aggregation can be utilized in various fields, such as cosmetics, pharmaceuticals, food, and drug delivery. However, the physicochemical properties and stability of emulsions are significantly affected by factors such as concentration, mixing method, droplet size, and temperature. Surfactants (emulsifiers), which are used to form stable emulsions, adversely affect the human body and environment and influence the properties of emulsions, thereby limiting their development. This study manufactured stable emulsions without a surfactant using ultrasonic equipment. The oil particle size distributions, zeta potentials, microscopic observations, and emulsion stabilities of six emulsions (with an oil content of 1 %) prepared using different frequencies (250–1000 kHz) and output powers (50–150 W) were analyzed, immediately after preparation at 25 °C and 3 d thereafter. Finally, it was possible to manufacture a stable emulsion without particle size change or phase separation with a particle size in the 100 nm range and a surface charge value of −40 mV or more under conditions of 400 kHz and 150 W. This study proposed a method (with the optimum conditions) for manufacturing surfactant-free emulsions by analyzing the stability of emulsions manufactured under various frequencies and output-power conditions. The proposed method could open new frontiers in emulsion development and applications.

Pickering emulsions of zein nanoparticles co-stabilized by Tween 20: An effective strategy to stabilize citral in low pH environment

The demand for surfactant-free emulsions is growing significantly in food industry. Herein, we report the fabrication of zein nanoparticles, modified their surface hydrophobicity with Tween 20, and used them to stabilize various formulations of Pickering emulsions designated as ZT0 %, ZT5 %, ZT10 %, ZT15 %, ZT20 %, and ZT25 %, for preventing the acid-catalysed degradation of citral at 25 °C. Our results suggest that, as the concentration of Tween 20 increases, the droplet size of the emulsions first increases and then decreases, whereas the mechanical strength continuously increases. Citral encapsulated in ZT25 % shows maximum physicochemical stabilization as determined by visual, olfactory and HPLC analysis, and when released in saline shows maximum antioxidant activity due to the favorable charge characteristics on Pickering emulsifiers, and the existence of hydrophobic ⇋ electrostatic interaction. As compared to prior literature, our work represents a significant advancement in fabrication of zein nanoparticles (ZNPs), their stabilization using Tween 20 and the formation of appropriate Pickering emulsions stabilized by Tween 20 modified ZNPs appropriate for modifying the interfacial characteristics of the emulsion for enhanced physicochemical stability, excellent aroma profile, controlled release rate, and improved antioxidant activity of encapsulated citral under harsh acidic conditions. Moreover, the novel Chemical Kinetic Method has been applied to analyze and interpret the citral stability as a function of interfacial parameters. The study, therefore presents a novel particle-surfactant complex interface, having great potential for the encapsulation, protection, and release of citral from the acidic food/pharmaceutical formulations.

Early stages of covalent organic framework formation imaged in operando

Covalent organic frameworks (COFs) are a functional material class able to harness, convert and store energy. However, after almost 20 years of research, there are no coherent prediction rules for their synthesis conditions. This is partly because of an incomplete picture of nucleation and growth at the early stages of formation. Here we use the optical technique interferometric scattering microscopy (iSCAT)1–3 for in operando studies of COF polymerization and framework formation. We observe liquid–liquid phase separation, pointing to the existence of structured solvents in the form of surfactant-free (micro)emulsions in conventional COF synthesis. Our findings show that the role of solvents extends beyond solubility to being kinetic modulators by compartmentation of reactants and catalyst. Taking advantage of these observations, we develop a synthesis protocol for COFs using room temperature instead of elevated temperatures. This work connects framework synthesis with liquid phase diagrams and thereby enables an active design of the reaction environment, emphasizing that visualization of chemical reactions by means of light-scattering-based techniques can be a powerful approach for advancing rational materials synthesis.

In situ growth of ZIF-8 on nanofibrous membrane for long-term ultra-high flux coalescence separation of oil-in-water emulsion

The presence of oil-in-water (O/W) emulsions poses a serious threat to the equilibrium of aquatic ecosystems, contaminates potable water resources, and disrupts the structure of soil layers. Consequently, there is an urgent need for effective and economically viable methods for removing emulsified oil droplets from water. The coalescence method has been proposed as an effective means of separating O/W emulsions. In this study, we developed an in situ growth strategy to decorate zeolitic imidazolate framework-8 (ZIF-8) on electrospun polyacrylonitrile (PAN) nanofibers for coalescence separation. The in situ growth process commenced with pretreatment to activate the PAN membrane, creating anchor sites for zinc ions, which was followed by immersion in precursors of ZIF-8 particles. The incorporation of ZIF-8 enhanced amphiphilicity, and roughness, and imparted a positive charge to the membrane, which was anticipated to effectively demulsify and coalesce oil droplets with a negative charge. The ZIF-8/PAN nanofiber membrane obtained a separation ratio exceeding 99.9 % for surfactant-free emulsions and 97.1 % for surfactant-stabilized emulsions. It also demonstrated an ultra-high permeation flux of 21,177 L m−2 h−1 and 14,118 L m−2 h−1, respectively, in a long-term continuous separation process.

Unique Crystallization Characteristics of Pickering High Internal Phase Emulsion Templated Porous Constructs.

To study the crystallization behavior of polymeric chains under the influence of porosity, the thermal properties of various nonporous and porous poly(ε-caprolactone) (PCL) based constructs were investigated. Porous cross-linked PCL nanocomposite constructs were fabricated utilizing in situ polymerization of CL-based surfactant-free Pickering high internal phase emulsions (HIPEs), stabilized using modified fumed silica nanoparticles (mSiNP) at a minimal concentration of 0.6 wt %. The corresponding nanocomposite constructs exhibited polyhedral pore morphology with significant pore roughness due to the presence of mSiNP. DSC thermograms of nonporous constructs illustrated diminished crystallization temperature and kinetics upon cross-linking and inclusion of mSiNP which confirmed suppressed mobility of polymer chains. Further introduction of porosity led to substantial supercooling, resulting in crystallization temperatures as low as -24 °C. Changes in the crystal structure of various nonporous and porous constructs were also studied using XRD. The crystallization behavior of porous constructs was finally evaluated using Jeziorny, Ozawa, and Mo theories under nonisothermal conditions. Significant deviation from the theoretical model, as observed in the case of porous constructs, implied a complex crystallization mechanism that eventually was not only controlled by the chain immobility due to cross-linking but also heterogeneity present in the wall thickness of the constructs. The unique melting-crystallization phenomenon observed in such constructs may further be expanded to other systems of high heat capacity for utilization as energy storage materials.

Future Created by Surfactant-free Emulsions ～Switching to Emulsification in the Absence of Surfactants～

Future Created by Surfactant-free Emulsions ～Switching to Emulsification in the Absence of Surfactants～

Comprehensive evaluation of non-conventional lanthanum phosphate nanospheres inside water-in-oil microemulsion scaffolds and their utilization in the assessment of surfactant-free TiO2-based Pickering emulsion formulations

A comprehensive evaluation is performed of lanthanum phosphate nanospheres in water-in-oil (W/O) microemulsion scaffolds and their utilization in the formulation of surfactant-free TiO2-based stable Pickering emulsions.

Ionically crosslinked cellulose nanocrystals by metal nitrates for the preparation of stable emulsions with tunable interface properties

Biologically extracted cellulose nanocrystals (CNCs) are rod-like and amphiphilic materials with surface-exposed (hydrophilic sites) and hidden (hydrophobic sites) hydroxyl groups. These physicochemical characteristics make CNCs suitable for use as emulsifying agents to stabilize emulsions. Stable oil-in-water emulsions, using sulfated (i.e., –SO3-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\ ext{SO}}}_{3}^{-}$$\\end{document}) CNCs that were ionically crosslinked with alkaline-earth (i.e., Mg2+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\ ext{Mg}}}^{2+}$$\\end{document}) or transition-d-block (i.e., Zn2+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\ ext{Zn}}}^{2+}$$\\end{document}) metal cations, were developed without the use of any synthetic surfactants or prior functionalization of pure CNCs with hydrophobic molecules. Various emulsion surface properties such as interfacial tension, surface charge, surface chemistry, as well as rheology were characterized. Ionically crosslinked CNCs (iCNCs) adsorbed at the interface of an oil and water and fortified the emulsion droplets (5–30 µm) against coalescence by lowering the interfacial tension from 65 mN/m (i.e., pure CNC mixture with oil) to 25 mN/m (i.e., iCNC mixture with oil) and reducing zeta potential with surface charge values (–30 mV to –10 mV), ideal to maintain droplet layer assembly at the water–oil interface. This study provided an alternative approach to achieve particle-stabilized and surfactant-free emulsions by using divalent metal nitrates to develop “clean” emulsion-based technologies for applications in many industries from agriculture to food to pharmaceuticals.

Investigating the effect of MnCl2 salt concentration on the droplet size and stability in a microfluidics droplets generation system

In the realm of droplet-based microfluidic systems, achieving optimal droplet size, shape, and distribution is crucial for efficient mass transfer and reaction performance. Traditionally, surfactants have been employed to modify interfacial properties and control droplet characteristics; however, they can impact reaction environments. A novel approach gaining traction is the creation of surfactant-free droplets, where additives are minimized to preserve the liquids' inherent properties. This study aims to investigate the creation of surfactant-free emulsions using divalent ions derived from Manganese(II) chloride (MnCl2) solutions. Emulsions play a vital role in various industries, but their stability often relies on surfactants. To address this, the research examines the influence of MnCl2 concentrations (ranging from 0.2 M to 1.0 M) on droplet dynamics within an oil phase using microfluidic analysis. Notably, a distinctive non-linear correlation between ion concentration and droplet size emerges, challenging conventional assumptions. This observation highlights the intricate and nuanced interfacial interactions governing surfactant-free emulsions, showcasing potential opportunities for designing stable emulsions without traditional surfactants. For instance, droplet sizes decreased from 171 µm to 138 µm as MnCl2 concentration increased from 0.2 M to 0.4 M, demonstrating this non-linear trend. However, further increases in MnCl2 concentration to 0.8 M and 1.0 M resulted in minimal changes in droplet size.

Surfactant-free gelatin-stabilised biodegradable polymerised high internal phase emulsions with macroporous structures.

High internal phase emulsion (HIPE) templating is a well-established method for the generation of polymeric materials with high porosity (>74%) and degree of interconnectivity. The porosity and pore size can be altered by adjusting parameters during emulsification, which affects the properties of the resulting porous structure. However, there remain challenges for the fabrication of polyHIPEs, including typically small pore sizes (∼20-50μm) and the use of surfactants, which can limit their use in biological applications. Here, we present the use of gelatin, a natural polymer, during the formation of polyHIPE structures, through the use of two biodegradable polymers, polycaprolactone-methacrylate (PCL-M) and polyglycerol sebacate-methacrylate (PGS-M). When gelatin is used as the internal phase, it is capable of stabilising emulsions without the need for an additional surfactant. Furthermore, by changing the concentration of gelatin within the internal phase, the pore size of the resulting polyHIPE can be tuned. 5% gelatin solution resulted in the largest mean pore size, increasing from 53μm to 80μm and 28μm to 94µm for PCL-M and PGS-M respectively. In addition, the inclusion of gelatin further increased the mechanical properties of the polyHIPEs and increased the period an emulsion could be stored before polymerisation. Our results demonstrate the potential to use gelatin for the fabrication of surfactant-free polyHIPEs with macroporous structures, with potential applications in tissue engineering, environmental and agricultural industries.

Ultrastable Emulsion Stabilized by the Konjac Glucomannan-Xanthan Gum Complex.

Surfactant-free emulsions are currently gaining increased interest due to their technofunctional, health-promoting, economic, biocompatible, and sustainable characteristics. Herein, we report an ultrastable, surfactant-free emulsion stabilized by the konjac glucomannan (KGM)-xanthan gum (XG) complex. The results suggested that KGM-XG tended to adsorb onto the oil/water interface, causing a reduction in interfacial tension. The emulsion droplets were less than 1 μm in diameter and had a narrow size distribution. Using laser confocal microscopy and cryo-SEM, it was observed that KGM-XG generated a compact film on the surface of emulsion droplets while simultaneously constructing a three-dimensional network in the continuous phase. Both of these factors contributed to the stability of the emulsion. The present study presents a straightforward approach for producing highly stable emulsions stabilized by polysaccharides. These emulsions can be effectively utilized to enhance the water resistance of cellulose paper, which is extensively employed in the packaging industry.

Constructing superwetting membranes by sodium lignosulfonate-modified carbon nanotube for highly efficient crude oil-in-water emulsions separations

For the past few years, superwetting materials had been developed to enhance the treatment process of oily wastewater. Membranes are improved through the combination of surface topography and chemical modifications to achieve superwetting properties for treating oily wastewater effectively. In this work, we prepared an eco-friendly membrane by depositing sodium lignosulfonate (SLS)-modified carbon nanotube (CNT) on a cellulose acetate membrane via vacuum filtration without employing any organic solvents. The SLS@CNT membrane shows superhydrophilicity and underwater superoleophobicity with high stability. Furthermore, the SLS@CNT membrane exhibits outstanding antifouling and self-cleaning properties against crude oil of high viscosity. Most importantly, our SLS@CNT membrane exhibits outstanding oil-in-water emulsions separation performances including crude oil-in-water emulsions. For the surfactant-free and surfactant-stabilized emulsions, fluxes were revealed to reach up to 27,800 L m−2 h−1 bar−1 and 13,800 L m−2 h−1 bar−1, respectively, with very high separation efficiency (>99.97 % and 99.79 %, respectively). The distinguished performance of our SLS@CNT membrane, and its eco-friendly, low-energy consumption, and cost-effective preparation, demonstrate practical applicability.

Underwater superoleophobic HKUST-1/PDA@SM membrane with excellent stability and anti-fouling performance for oil-in-water emulsion separation

Owing to having small particle size, complex system and high degree of emulsification, traditional separation methods have shown difficulties to achieve good separation effect of oil-water emulsion system. Despite this truth, the rapid development of membrane separation technology has indicated an excellent separation performance. However, the membrane stability and membrane fouling are still prominent problems, and the research on demulsification-separation process is not in-depth, which restricts the further development of membrane separation technology for practical industrial applications. Therefore, in present work, an underwater superoleophobic HKUST-1/PDA@SM membrane was prepared via the combination of step-by-step deposition and secondary growth method. The as-prepared membrane showed an excellent anti-fouling performance with flux recovery ratio of over 95%. The HKUST-1/PDA@SM membrane could accomplish the selective separation of surfactant-free and surfactant-stabilized emulsions under gravity-driven condition. Further, the as-prepared membrane presented an excellent mechanical stability, chemical stability, thermal stability, and recyclability. More importantly, the analysis of membrane fouling mechanism disclosed that the most fundamental reason for membrane fouling was the blockage of membrane pores. Furthermore, we firstly proposed the assumption of the migration-transformation of emulsifier in the emulsion separation process, and then it was verified that most of emulsifier entered into the filtrate. Finally, the membrane demulsification-separation mechanism was discussed precisely. Overall, HKUST-1/PDA@SM membrane with excellent stability and anti-fouling performance has a broad practical application prospect for oil-water emulsion separation.

Stabilization of a Pickering Emulsion by Nanoparticles of Eudragit RSPO and Pol-epsilon Caprolactone: Contact Angle Measurement and Surface Tension Studies

The use of colloidal particles to prepare and stabilize emulsions, known as "Pickering emulsions “, has aroused growing interest in recent years. Pickering and Ramsden demonstrated at the beginning of the last century the feasibility of surfactant-free emulsions, in presence of these emulsions is called "Pickering Emulsions". This concept of emulsions stabilized by solid particles is experiencing renewed interest nowadays given the many advantages it offers good stability, environmental protection, user safety, and particle varieties.&#x0D; The first part is devoted to the synthesis of Eudragit RSPO and pol epsilon-caprolactone nanoparticles and their characterization. The characterization of the nanoparticles is performed by dynamic light scattering and geometry. The understanding of the interfacial behavior of these nanoparticles and their associated stabilization mechanisms for emulsions was carried out. The second part of the study investigated the formulation and stabilization of the emulsion using the washed suspension containing the nanoparticles as the only stabilizer. The objective of this part is to stabilize and characterize the formulated emulsions. Droplet size determination and microscopy were performed using a Zeiss optical microscope. The direction of the formulated emulsions was determined by conductimetry. In conclusion, Pickering emulsions stabilized solely by Eudragit RSPO and Poly-epsilon Caprolactone nanoparticles appear to be highly effective innovative drug carriers, opening new doors as potential drug delivery systems.

O/W Pickering emulsion stabilized by magnesium carbonate particles for drug delivery systems

This study investigates the formulation of surfactant-free Pickering emulsions that release a drug at a specific pH to improve its oral bioavailability. The stabilizing particles composed of magnesium carbonate particles. Pickering oil-in-water emulsions stabilized with magnesium carbonate particles and encapsulating a hydrophobic drug model (ibuprofen) were formulated using a high-energy process with rotor-stator turbo mixer (IKA® T25 digital ultra-Turrax). The experimental approach explored the impact of all formulation parameters, dispersed phase and amount of magnesium carbonate particles on the physicochemical properties of Pickering emulsions. The O/W Pickering emulsion was characterized by a methylene blue test, pH and conductivity measurements, and droplet size determination. In addition, Pickering emulsions stabilized by magnesium carbonate particles have the advantage of being destabilized in acidic medium leading to the release of the active principle via the droplets. The acidic medium release study (pH equal to 1.2) showed ibuprofen release as a function of initial droplet loading and saturation concentration. In the simulated intestinal medium at pH equal to 6.8, we found a better release of ibuprofen from emulsions that already had saturation in an acid medium. Thus, the interest of these Pickering emulsions lies on the fact that their non-toxicity and magnesium carbonate particles allow destabilization of the emulsions and release of the drug. These emulsions not only protect patients from the side effects of acid-based drugs, but also contribute to increase the bioavailability of these acidic drugs.&#x0D; Keywords: emulsion -Pickering-magnesium carbonate- ibuprofen-oral bioavailability

Stability and Application Properties of Surfactant-Free Cosmetic Emulsions: An Instrumental Approach to Evaluate Their Potential

Technological innovation in the cosmetic field must necessarily consider not only the safety and efficacy requirements but also the growing attention to environmental issues and the need for sensory pleasure during application to satisfy the consumers’ expectations. This work aimed to formulate an oil-in-water fluid emulsion stabilized by the combination of organic and inorganic powders, namely Zea mays starch and zinc oxide associated at different ratios in presence of a polysaccharidic rheological modifier. After verifying the physical stability of the prototypes with a mechanical stress test in a centrifuge, the rheological analyses were conducted in continuous and oscillatory flow conditions, and the immersion/de-immersion test, conducted using a texture analyzer, allowed identifying the system with the viscoelastic characteristics and the parameters of textures, such as firmness, consistency, and adhesiveness, more suitable for the formulation of skin-care products with low viscosity and high spreadability. Finally, we studied the compatibility of the powders with sunscreen filters and pigments, to optimize the systems and assess their potential use in finished products.

Shedding light on the formation and stability of mesostructures in ternary “Ouzo” mixtures

Hypothesis: Ternary systems made of water, a water-miscible solvent, and hydrophobic solutes spontaneously produce metastable particles by the “Ouzo effect” and thermodynamically stable “Surfactant-Free Micro Emulsions” (SFME). However, the use of different analyses has led to a variability in the criteria to determine the boundaries of the Ouzo domain. We hypothesized that this could be clarified by investigating the stability and the physical state of the particles.Experiments: We investigate four systems using both solid and liquid solutes and two different solvents, and achieved a careful investigation of their phase diagrams, using DLS, Nanoparticle Tracking Analysis, NMR, Multiple Light Scattering, electrophoretic mobility, and fluorescence analysis.Findings: Our results evidence that the transition from the monophasic to the Ouzo domains does not coincide with the cloudiness curve, and that compositions in the Ouzo domain can look fully transparent, in contrast to what is often considered. This transition is best determined by stability analysis. The cloudiness curve corresponds to the formation of particles with a large size dispersity. In the Ouzo domain, we observed an exchange of solute between the continuous phase and solute particles swollen with solvent. In addition, the particles are stabilized against coalescence by their high negative charge.

Controllable emulsification by dissolved gas in water: Formation and stability of surfactant-free oil nanodroplets

Surfactant-free emulsions represent the ideal system to investigate properties like droplet size, surface potentials, and colloidal stability which are mainly driven by oil-water interactions. The dissolved gases in solution, which are often neglected due to low solubility, have been found to pose significant impacts in the dispersion process. So far, the role of dissolved gases in the emulsions system remains unclear. Here, we systematically studied the effect of different concentrations of dissolved gases in water on the formation and stability of surfactant-free oil nanodroplets. By increasing the dissolved gas in water, more concentrated and smaller nanodroplets were produced by ultrasonication but with a lowered growth rate. While the removal of dissolved gas severely restricted the emulsification process and only a few nanodroplets were produced. The growth pattern of nanodroplets in different gas-saturated water is similar, first increasing rapidly and reaching equilibrium eventually. The stability of nanodroplets is found to be largely independent of the dissolved gas in water. The growth mechanisms for surfactant-free nanodroplets in gas-oversaturated water possibly combine Ostwald ripening, coalescence, and creaming. Our study will offer valuable insights into the production of nanoemulsions, oil-water separation, and constraints on ultrasonication.