Spontaneous Emulsification Process Research Articles

The influence of electrolyte on the emulsified layer at the water/hexadecane interface

This study quantifies the impact of electrolytes on the emulsifier’s diffusivity within an intermediate layer at a liquid-liquid interface during the spontaneous emulsification process. In this new technique, the mass transfer coefficient of the non-ionic amphiphilic molecules through the layer was investigated experimentally using a single oil droplet monitored photographically. The flux of the spontaneous emulsification process of hexadecane was measured with the presence of an emulsifier, Triton X-100, dissolved in either the aqueous or oil phase. The obtained data was employed to quantify the influence of electrolytes (NaCl, KCl, CaCl2 and MgCl2) on the diffusivity of surfactant molecules within the intermediate layer. The result shows that the diffusivity of the surfactant is proportional to the electrolyte concentration due to the increased packing of diffusing molecules. The influences of electrolytes on the diffusivity follow the order of NaCl > MgCl2 > KCl > CaCl2. Quantifying the mass transfer coefficient of surfactant molecules through the intermediate layer provides a mathematical framework to predict the overall emulsification kinetics. The modelling framework can be expanded to different emulsification systems which are controlled by the interaction between electrolytes and non-ionic surfactants.

Airborne Ouzo: Evaporation-induced emulsification and phase separation dynamics of ternary droplets in acoustic levitation

We experimentally investigated the evaporation dynamics of acoustically levitated Ouzo droplets (a mixture of ethanol, water, and anise oil). Acoustic levitation has gained significant attention in various fields owing to its potential to create a lab-in-a-drop. Although evaporation is a key process in nature and industry, many studies have focused on single and binary components, and ternary droplets in acoustic levitation have rarely been experimentally investigated. In this study, the evaporation-induced spontaneous emulsification (the Ouzo effect) and phase separation process at 40–90 vol. % ethanol were visualized. We estimated the concentration change by evaporation of each component in the levitated ternary droplets based on an evaporation model to determine the experimental results. Our experimental results revealed four distinct stages of evaporation in levitated Ouzo droplets: (1) preferential evaporation of the volatile component (ethanol), (2) spontaneous emulsification (myriad micro-oil droplets generation), (3) phase separation forming a core–shell droplet, and (4) water evaporation completion resulting in the remaining oil droplets. Finally, we analyzed the emulsification process using a spacetime diagram. These findings suggest that acoustic levitation is suitable for physicochemical manipulation in mid-air.

Self-Assembly and In Situ Quaternization of Triblock Bottlebrush Block Copolymers via Organized Spontaneous Emulsification for Effective Loading of DNA.

Microspheres bearing large pores are useful in the capture and separation of biomolecules. However, pore size is typically poorly controlled, leading to disordered porous structures with limited performances. Herein, ordered porous spheres with a layer of cations on the internal surface of the nanopores are facilely fabricated in a single step for effective loading of DNA bearing negative charges. Triblock bottlebrush copolymers (BBCPs), (polynorbornene-g-polystyrene)-b-(polynorbornene-g-polyethylene oxide)-b-(polynorbornene-g-bromoethane) (PNPS-b-PNPEO-b-PNBr), are designed and synthesized for fabrication of the positively charged porous spheres through self-assembly and in situ quaternization during an organized spontaneous emulsification (OSE) process. Pore diameter as well as charge density increase with the increase of PNBr content, resulting in a significant increase of loading density from 4.79 to 22.5ngµg-1 within the spheres. This work provides a general strategy for efficient loading and encapsulation of DNA, which may be extended to a variety of different areas for different real applications.

Quantifying the spontaneous emulsification of a heavy hydrocarbon with the presence of a strong surfactant

The rate of spontaneous emulsification phenomenon of heavy hydrocarbon in a non-ionic surfactant solution was studied experimentally. The size of a diminishing oil droplet was monitored photographically with the presence of an electrolyte. The obtained data were analysed using Axisymmetric Drop Shape Analysis (ADSA) software to measure the flux of emulsion droplets formed spontaneously. In contrast to all previous reports, a stable layer confined between the oil and aqueous solution was observed with a relatively constant thickness, ∼ 100 µm. The result shows that the rate of emulsification is reduced with the presence of electrolytes and is inversely correlated to its concentration. Considerable variation of the influence of electrolyte type on the kinetic of the spontaneous emulsification process for a given condition has been observed. Consequently, a new diffusion-control mechanism has been proposed, creating an extendable model to describe the process theoretically. The experimental data of emulsifying hexadecane in Triton X-100 micellar solution with the presence of potassium chloride and sodium chloride was well fitted to the proposed model. The results have important implications for surfactant-based cleaning processes.

Interfacial Self-Assembly of Amphiphilic Core-Shell Bottlebrush Block Copolymers Toward Responsive Photonic Balls Bearing Ionic Channels.

Photonic balls can be facilely obtained through interfacial self-assembly of amphiphilic bottlebrush block polymers (BBCPs) within a water-in-oil-in-water (w/o/w) multiple emulsion system, and polystyrene (PS) has been employed as the skeleton of the balls showing no responsive properties. Here, the design and synthesis of core-shell BBCPs are demonstrated with a poly(tert-butyl acrylate)-block-polystyrene (PtBA-b-PS) block copolymer as the hydrophobic side chains and poly(ethylene glycol) as the hydrophilic block. Interfacial self-assembly of the core-shell BBCPs within shrinking droplets produces porous microspheres with full-spectrum structural colors through an organized spontaneous emulsification process. The PtBA core wrapped by PS in the skeleton of the balls can be converted into polyacrylic acid (PAA) forming an ionic channel responsive to pH variations. Consequently, the hydrolyzed photonic balls show different colors under different pH conditions dependent on varying degrees of ionization and hydration of the PAA channel. Reflected colors can be verified using an optical spectrometer, providing an effective strategy for precise pH indication.

Propylene Glycol Caprylate-Based Nanoemulsion Formulation of Plumbagin: Development and Characterization of Anticancer Activity.

Plumbagin, a bioactive naphthoquinone, has demonstrated potent antitumor potential. However, plumbagin is a sparingly water-soluble compound; therefore, clinical translation requires and will be facilitated by the development of a new pharmaceutical formulation. We have generated an oil-in-water nanoemulsion formulation of plumbagin using a low-energy spontaneous emulsification process with propylene glycol caprylate (Capryol 90) as an oil phase and Labrasol/Kolliphor RH40 as surfactant and cosurfactant excipients. Formulation studies using Capryol 90/Labrasol/Kolliphor RH40 components, based on pseudoternary diagram and analysis of particle size distribution and polydispersity determined by dynamic light scattering (DLS), identified an optimized composition of excipients for nanoparticle formulation. The nanoemulsion loaded with plumbagin as an active pharmaceutical ingredient had an average hydrodynamic diameter of 30.9 nm with narrow polydispersity. The nanoemulsion exhibited long-term stability, as well as good retention of particle size in simulated physiological environments. Furthermore, plumbagin-loaded nanoemulsion showed an augmented cytotoxicity against prostate cancer cells PTEN-P2 in comparison to free drug. In conclusion, we generated a formulation of plumbagin with high loading drug capacity, robust stability, and scalable production. Novel Capryol 90-based nanoemulsion formulation of plumbagin demonstrated antiproliferative activity against prostate cancer cells, warranting thus further pharmaceutical development.

Water-in-Oil Nano-Emulsions Prepared by Spontaneous Emulsification: New Insights on the Formulation Process.

Nano-emulsions consist of stable suspensions of nano-scaled droplets that have huge loading capacities and are formulated with safe compounds. For these reasons, a large number of studies have described the potential uses of nano-emulsions, focusing on various aspects such as formulation processes, loading capabilities, and surface modifications. These studies typically concern direct nano-emulsions (i.e., oil-in-water), whereas studies on reverse nano-emulsions (i.e., water-in-oil) remain anecdotal. However, reverse nano-emulsion technology is very promising (e.g., as an alternative to liposome technology) for the development of drug delivery systems that encapsulate hydrophilic compounds within double droplets. The spontaneous emulsification process has the added advantages of optimization of the energetic yield, potential for industrial scale-up, improved loading capabilities, and preservation of fragile compounds targeted for encapsulation. In this study, we propose a detailed investigation of the processes and formulation parameters involved in the spontaneous nano-emulsification that produces water-in-oil nano-emulsions. The following details were addressed: (i) the order of mixing of the different compounds (method A and method B), (ii) mixing rates, (iii) amount of surfactants, (iv) type and mixture of surfactants, (v) amount of dispersed phase, and (vi) influence of the nature of the oil. The results emphasized the effects of the formulation parameters (e.g., the volume fraction of the dispersed phase, nature or concentration of surfactant, or nature of the oil) on the nature and properties of the nano-emulsions formed.

Nanoemulsion boosts anesthetic activity and reduces the side effects of Nectandra grandiflora Nees essential oil in fish

Nectandra grandiflora essential oil has become an alternative to synthetic anesthetics and sedation in fish. However, essential oil volatility, light sensitivity, and low water-solubility may limit its use in the fish farm. To overcome these drawbacks, we developed a new nanoemulsion product that may be applied as an anesthetic. We evaluated the anesthetic property and safety of free essential oil (FEO) and its nanoemulsion (NEN) for Nile tilapia (Oreochromis niloticus). Formulations were made using the spontaneous emulsification process, and stability was tested for NEN and FEO at 4, 25, and 40 °C for 90 days. The NEN contained 95% of FEO, the major compounds remained stable up to 60 days, and the NEN protected the active substances at all temperatures. Fish behavior was observed during a bath with FEO and NEN 3–300 mg/L concentrations for 30 min. The difference between sedated and anesthetized fish was detected by their swimming behavior and response to stimuli on the caudal peduncle. Behavior score, survival, or adverse effects were accessed with 10 and 30 mg/L concentrations of FEO and NEN during 24 h exposure and 72 h recovery. Only 100 mg/L of NEN induced anesthesia without side effects. Long-term exposure tests confirmed the 30 mg/L NEN safety, with a 100% survival rate for fish exposed to NEN and a 25.5% survival rate for fish exposed to surfactants. Therefore, this poorly water-soluble essential oil was converted into a novel sedative and anesthetic for fish through nanoemulsion. Thus, nanoemulsion protects the essential oil and improves the pharmacological activity, with the suggested use of 30 mg/L during 24 h, for sedation, and 100 mg/L, for anesthesia.

Dynamics of acoustically levitated drops with Ouzo effect

Ouzo effect represents a typical spontaneous emulsification process, which is widely used in many fields such as chemical industry, biomedicine and fabrication of novel materials. This work attempts to clarify the influence of sound field and container-free conditions on Ouzo effect by combining Ouzo transition with the action of sound field. We compare the dynamic process by performing experiments on a glass slide and in an acoustic levitator, respectively, through triggering Ouzo effect via evaporation and droplet coalescence. We observe the evaporation-induced Ouzo transition, and the growth of emerged oil droplet satisfies the Fick’s law suggesting the droplet growth is dominated by diffusion. Under acoustic levitation, the Ouzo effect driven by droplet evaporation produces small droplets of divinylbenzene that rapidly diffuse with convection in the droplet and distribute uniformly throughout the droplet until only continuous droplet remains. Droplet coalescence could result in Ouzo transition and lead to the abnormal shape of levitated drop, which contains micron-sized oil droplets under acoustic levitation. By decreasing the intensity of sound field, the Ouzo droplet returns to an axisymmetrical shape and then recovers to its initial shape upon enhancing the sound intensity, indicating that the flow field in the droplet plays an important role in maintaining the irregular shape of Ouzo droplet. The abnormal shape of droplet is caused by both the internal flows and the acoustic radiation pressure exerted on the drop surface. This study may shed light on the developing of new techniques for micro-emulsification and fabrication of related materials.

Controlling water transport between micelles and aqueous microdroplets during sample enrichment

Droplet microfluidics technologies have advanced rapidly, but enrichment in droplets has still been difficult. To deterministically control the droplet enrichment, the water transport from an aqueous microdroplet in organic continuous phase containing span 80 micelles was investigated. Organic phase containing Span-80-micelles contacted a NaCl aqueous solution to control hydration degree of the micelles, prior to being used in the microfluidic device. Then, the organic phase was continuously applied to the microdroplets trappled in microwells. Here, water was transported from the microdroplet to the organic phase micelles. This spontaneous emulsification process induced the droplet shrinkage and stopped when the microdroplet reached a certain diameter. The micelle hydration degree correlated well with the final water activity of droplets. The enrichment factor can be determined by the initial microdroplet salt concentration and by the micelle hydration degree. As a proof-of-concept experiment, enrichment of fluorescent nanoparticles and dye was demonstrated, and fluorescent resonance energy transfer was observed as expected. Another demonstration of bound-free separation was performed utilizing the avidin-biotin system. This technique has the potential to be a powerful pretreatment method for bioassays in droplet microfluidics.

Effects of hydrophobic/hydrophilic blocks ratio on PS-b-PAA self-assembly in solutions, in emulsions, and at the interfaces

Composite organized molecular assemblies of amphiphilic block copolymers exhibit various properties and functionalities and have attracted much attention recently. Many research studies have focused on adjusting these properties by varying the fabrication approach and by controlling the morphology of the aggregates. This work involved an investigation of the self-assembly behavior of a series of polystyrene-b-polyacrylic acid (PS-b-PAA) homologues with different block ratios in water-in-oil (W/O) and oil-in-water (O/W) emulsions. These emulsions simultaneously formed via a spontaneous emulsification process across the liquid/liquid interface. A variety of aggregates of the polymers with metal ions were obtained, including microcapsules, spherical micelles, rod-like and disc-like micelles, vesicles, and interior microphase-separated particles. These structures formed either in the emulsion droplets or in the continuous phase, and then proceeded to adsorb at the air/liquid interface or the planar liquid/liquid interface to form thin films. The influence of the molecular structure, the concentration of the metal ions, and the nature of the metal ion on the self-assembly behavior of the polymer molecules and the aggregate morphologies is discussed. In addition, these composite structures are shown to exhibit higher catalytic activity and good stability for the hydrogenation of nitroarenes in aqueous solutions.

Spontaneous ethanol–water emulsification as a precursor for porous particle formation: Understanding the role of dissolved carbohydrates

Quiescent mixing of aqueous lactose solution with ethanol by gentle pouring allowed controlled observation of a transient, spontaneous emulsification process between ethanol and water. This phenomenon contrasts with the conventional stable phase-separation process for ethanol–water systems with other solutes. The presence of lactose in the dissolved state was deduced to be the key factor causing spontaneous emulsification. This explains the transitional behavior of the phenomenon. Further experiments with aqueous maltodextrin solution, using the same experimental technique, confirmed this phenomenon. The mechanisms determined in this work will form the basis of porous-particle synthesis via the antisolvent vapor-precipitation technique.

Hydrophobin-stabilized nanoemulsion produced by a low-energy emulsification process: A promising carrier for nutraceuticals

Hydrophobin II (HFBII) is an amphiphilic biopolymer that could be explored to stabilize oil-in-water nanoemulsions as nutraceutical delivery systems. This study reports the production of HFBII-stabilized nanoemulsions by a spontaneous emulsification process using copaiba oil as a bioactive lipid. HFBII was isolated from a wild-type Trichoderma reesei and characterized. A 23 full factorial design with three central points was used to obtain an optimal nanoemulsion system, whose physical-chemical properties were studied under different ionic strength and pH. The peptide similarity search allowed the identification of a series of 6 ion fragments from the isolated fraction, which can be attributed to the amino acid sequences of the HFBII database. The optimal nanoemulsion system presented a nanoscale droplet size (<200 nm), a narrow size distribution (PDI <0.2) and a negative zeta potential of ≈ −30 mV, which was stable at low salt content and pH values close to the neutrality. These results demonstrated the feasibility of using HFBII as a biopolymer to stabilize nanoemulsion systems. Furthermore, the HFBII-stabilized nanoemulsion is a promising carrier for nutraceuticals in food technology applications.

Pickering emulsion stabilized by cashew gum- poly-l-lactide copolymer nanoparticles: Synthesis, characterization and amphotericin B encapsulation.

In this work, we provide proof-of-concept of formation, physical characteristics and potential use as a drug delivery formulation of Pickering emulsions (PE) obtained by a novel method that combines nanoprecipitation with subsequent spontaneous emulsification process. To this end, pre-formed ultra-small (d.∼10 nm) nanoprecipitated nanoparticles of hydrophobic derivatives of cashew tree gum grafted with polylactide (CGPLAP), were conceived to stabilize Pickering emulsions obtained by spontaneous emulsification. These were also loaded with Amphotericin B (AmB), a drug of low oral bioavailability used in the therapy of neglected diseases such as leishmaniasis. The graft reaction was performed in two CG/PLA molar ratio conditions (1:1 and 1:10). Emulsions were prepared by adding the organic phase (Miglyol 812®) in the aqueous phase (nanoprecipitated CGPLAP), resulting the immediate emulsion formation. The isolation by centrifugation does not destabilize or separate the nanoparticles from oil droplets of the PE emulsion. Emulsions with CGPLAP 1:1 presented unimodal distributions at different CGPLA concentration, lower values in size and PDI and the best stability over time. The AmB was incorporated in the emulsions with a process efficiency of 21-47%, as determined by UV-vis. AmB in CGPLAP emulsions is in less aggregated state than observed in commercial AmB formulation.

Alpha tocopherol loaded chitosan oleate nanoemulsions for wound healing. Evaluation on cell lines and ex vivo human biopsies, and stabilization in spray dried Trojan microparticles

An amphiphilic chitosan salt, chitosan oleate (CS-OA), was previously proposed for the physical stabilization of lemongrass antimicrobial nanoemulsions (NE) through a mild spontaneous emulsification process. As both chitosan and oleic acid are described in the literature for their positive effects in wound healing, in the present study CS-OA has been proposed to encapsulate alpha tocopherol (αTph) in NEs aimed to skin wounds. A NE formulation was developed showing about 220 nm dimensions, 36% drug loading, and αTph concentration up to 1 mg/ml.Both CS-OA and αTph NE stimulated cell proliferation on keratinocytes and fibroblast cell cultures, and in ex vivo skin biopsies, suggesting the suitability of CS-OA and of the antioxidant agent for topical application in wound healing.αTph stability was further improved with respect of encapsulation, by spray drying the NE into a powder (up to about 90% αTph residual after 3 months). The spray drying process was optimized, to improve powder yield and αTph recovery, by a design of experiments approach. The powder obtained was easily re-suspended to deliver the NE and resulted able to completely release αTph.

A novel ionic amphiphilic chitosan derivative as a stabilizer of nanoemulsions: Improvement of antimicrobial activity of Cymbopogon citratus essential oil

Amphiphilic chitosans have been recently proposed to improve delivery of poorly soluble drugs. In the present paper a derivative obtained by ionic interaction between chitosan and oleic acid was for the first time studied to physically stabilize o/w nanoemulsions of an antimicrobial essential oil, Cymbopogon citratus (Lemongrass), in a low energy and mild conditions emulsification process.The novel combination of spontaneous emulsification process with chitosan oleate amphiphilic properties resulted in a stable dispersion of a few hundred nanometer droplets. Positive zeta potential confirmed the presence of a chitosan shell around the oil droplets, which is responsible for the nanoemulsion physical stabilization and for the maintenance of chitosan bioactive properties, such as mucoadhesion. Cytotoxicity test was performed on four different cell lines (HEp-2, Caco-2, WKD and McCoy cells) showing biocompatibility of the system. The maintenance and in some cases even a clear improvement in the essential oil antimicrobial activity towards nine bacterial and ten fungal strains, all of clinical relevance was verified for Lemongrass nanoemulsion.

Comparison of 2 strategies to enhance pyridoclax solubility: Nanoemulsion delivery system versus salt synthesis

Pyridoclax is an original oligopyridine lead, very promising in treatment of chemoresistant cancers. However, from solubility measurement and permeability evaluation, it appeared that this compound can be considered as a BCS II drug, with a poor water solubility. To overcome this unfavorable property, two strategies were proposed and compared: pyridoclax di-hydrochloride salt synthesis and formulation of pyridoclax-loaded nanoemulsions (PNEs) efficiently performed by transposing the spontaneous emulsification process previously developed by our team. Whereas the salt improved the thermodynamic solubility of the drug by a factor 4, the apparent solubility of the encapsulated pyridoclax was 1000-fold higher. Their stability was assessed upon dilution in various complex biomimetic media relevant for oral administration (SGF, FaSSIF-V2, FeSSIF-V2) or for the intravenous route (PBS). The solubility of the salt was affected by the nature of the medium, indicating that it could precipitate after administration, negatively impacting its bioavailability and its efficiency in vivo. On the contrary, in all media, PNEs remained stable in terms of granulometric properties (determined by DLS), ζ-potential and encapsulation efficiency (measured by HPLC). Thus, such nanomedicines appear as a valuable option to perform preclinical studies on the promising pyridoclax.

Ferulic Acid Lecithin-Based Nano-Emulsions Prepared by Using Spontaneous Emulsification Process

Ferulic acid (4-hydroxy-3-methoxycinnamic acid), an effective component of medical plant, is a phenolic acid with low toxicity that can be absorbed and easily metabolized in the human body. The solubility of Ferulic Acid (FA) is very low in aqueous solutions which can cause problem in preparation of pharmaceutical products, but it can easily be dissolved in oil/water interface of nano-emulsions. In the present work, a kind of ferulic acid nano-emulsion was prepared using the spontaneous emulsification method which occurs when an organic phase and an aqueous phase are mixed. A chemometrics approach has been used to optimize the size of FA nanoemulsions.�The experiments were performed according to a Box-behenken experimental design, one of the most suitable experimental design for modeling studies. The effect of three experimental parameters on droplet size was studied using multivariate analysis. The factors studied and the related levels were the concentration of lecithin (0.7-2 % w/w, in aqueous phase), the concentration of tween-80 (2-8 % w/w, in aqueous phase) and sounication time (10-45 minutes). In all the experiments, the water phase was added to the organic phase including lecithin, tween-80 and FA in ethanol solvent. Then experimental droplet sizes were fitted to the polynomial model. Good descriptive and predictive ability of the model was verified as high values of the statistics R 2 (0.996) and F (112.5) were obtained for the linear relationship between predicted and experimental values of the dependent variable.

An experimental study on particle formation in emulsifier-free emulsion polymerization of styrene

Particle formation in polymerization of styrene induced within two stratified layers of a monomer and water containing an initiator was studied in the absence of emulsifiers and stirring. A polymerization-induced decrease of interfacial surface tension was observed. The particle size distribution was characterized by dynamic light scattering during polymerization. The results confirm particle nucleation through spontaneous emulsification process.

The Effect of Nanoparticles Crystallite Size on the Recovery Efficiency in Dielectric Nanofluid Flooding

Application of nanotechnology in enhanced oil recovery (EOR) has been increasing in recent years. After secondary flooding, more than 60% of the original oil in place (OOIP) remains in the reservoir due to trapping of oil in the reservoir rock pores. One of the promising EOR methods is surfactant flooding, where substantial reduction in interfacial tension between oil and water could sufficiently displace oil from the reservoir. In this research, instability at the interfaces is created by dispersing 0.05 wt% ZnO nanoparticles in aqueous sodium dodecyl sulfate (SDS) solution during the core flooding experiment. The difference in the amount of particles adsorbed at the interface creates variation in the localized interfacial tension, thus induces fluid motion to reduce the stress. Four samples of different average crystallite size were used to study the effect of particle size on the spontaneous emulsification process which would in turn determine the recovery efficiency. From the study, ZnO nanofluid which consists of larger particles size gives 145% increase in the oil recovery as compared with the smaller ZnO nanoparticles. In contrast, 63% more oil was recovered by injecting Al2O3nanofluid of smaller particles size as compared to the larger one. Formation of a cloudy solution was observed during the test which indicates the occurrence of an emulsification process. It can be concluded that ultralow Interfacial tension (IFT) value is not necessary to create spontaneous emulsification in dielectric nanofluid flooding.