Coalescence Of Oil Droplets Research Articles

Stable and Temperature‐Responsive Surfactant‐Free Foamulsions with High Oil‐Volume Fraction

There is more than foam: Optical microscopy images (with false colouring, see picture) depicting quick destabilization (within minutes) of foamulsions due to the coalescence of densely-packed oil droplets when heated at higher temperatures (65 °C).

Electrostatic Enhancement of Coalescence of Oil Droplets (in Nanometer Scale) in Water Emulsion

Oil droplets in nanometer scale which are dispersed in water cannot be separated easily. An attractive technique is carried out by electrical phenomena to demulsify oil in water emulsion. In this research, non-uniform electric field or dielectrophoresis (DEP) is applied to remove sunflower oil (which is dispersed in the water). Effects of temperature, time and voltage (using AC-electric field) were considered to get the highest DEP-force (Fdi) and the best results. The oil particles sizes with average of approximately 76 nm have been shown using a ZetaSizer Nano ZS, Model ZEN 1600 (Malvern Instrument Ltd.). The maximum separation efficiency of 85% is obtained at the optimum temperature of 38°C and voltage of 3000 V.

Coalescence of oil droplets in plasticized starch matrix in simple shear flow

The formation of oil droplets in plasticized starch matrices is studied by using well-defined conditions similar to extrusion. A method based on double staining and confocal scanning microscopy was developed to investigate the role of coalescence during droplet formation. The results indicate that coalescence takes place at all process conditions studied. The apparent critical capillary number was used to quantify the coalescence intensity and to separate the influence of interdependent process parameters on the coalescence. The intensity of coalescence increased with shear rate and oil content whereas an increase in blend viscosity reduced the extent of coalescence. Besides, the results showed that the critical dispersed phase concentration (Φc), below which no coalescence takes place, depends on applied shear rate and decreases with increasing shear rate.

Physical properties of emulsion-based hydroxypropyl methylcellulose films: Effect of their microstructure

The initial characteristics of emulsions and the rearrangement of the oil droplets in the film matrix during film drying, which defines its microstructure, has an important role in the physical properties of the emulsion-based films. The objective of this work was to study the effect of the microstructure (two droplet size distributions) and stability (with or without surfactant) of HPMC oil-in-water emulsions over physical properties of HPMC emulsion-based edible films. HPMC was used to prepare sunflower oil-in-water emulsions containing 0.3 or 1.0% (w/w) of oil with or without SDS, as surfactant, using an ultrasonic homogenizer. Microstructure, rheological properties and stability of emulsions (creaming) were measured. In addition, microstructure, coalescence of oil droplets, surface free energy, optical and mechanical properties and water vapor transfer of HPMC films were evaluated. Image analysis did not show differences among droplet size distributions of emulsions prepared at different oil contents; however, by using SDS the droplet size distributions were shifted to lower values. Volume mean diameters were 3.79 and 3.77μm for emulsions containing 0.3 and 1.0% without surfactant, respectively, and 2.72 and 2.71μm for emulsions with SDS. Emulsions formulated with 1.0% of oil presented higher stability, with almost no change during 5 and 3 days of storage, for emulsions with and without SDS, respectively. Internal and surface microstructure of emulsion-based films was influenced by the degree of coalescence and creaming of the oil droplets. No effect of microstructure over the surface free energy of films was found. The incorporation of oil impaired the optical properties of films due to light scattering of light. Addition of oil and SDS decreased the stress at break of the emulsion-based films. The replace of HPMC by oil and SDS produce a lower “amount” of network structure in the films, leading to a weakening of their structure. The oil content and SDS addition had an effect over the microstructure and physical properties of HPMC-based emulsions which lead to different microstructures during film formation. The way that oil droplets were structured into the film had an enormous influence over the physical properties of HPMC films.

A new classification of a preovulatory oocyte maturation stage suitable for the synchronization of ovulation in controlled reproduction of Eurasian perch, Perca fluviatilis L

To improve controlled reproduction of Eurasian perch Perca fluviatilis, the criteria for the evaluation of final oocyte maturation stages were revised. The new classification covers six preovulatory maturational stages (I -VI) from the end of vitellogenesis to germinal vesicle breakdown (GVBD) and was based on macroscopic changes of preovulatory oocytes (position of the germinal vesicle, GVBD, oil droplets coalescence). The observation was performed during out-of-season artificial reproduction with the use of a single hCG injection (500 IU/kg). The classification was subsequently verified with the controlled reproduction of wild female perch with the use of hormonal stimulation (500 IU hCG/kg of body weight at 12°C). The females were at different maturational stages and constituted respective experimental groups (I-VI). During the experiment, ovulation appeared to be considerably synchronized within particular groups. Statistical differences in latency time (time between hormonal treatment and ovulation) were found between experimental groups (mean latency time: 110, 92, 68, 49, 29 and 18 h in groups representing VI, V, IV, III, II and I stage of the proposed classification, respectively). The proposed classification and the results presented in the study allowed for effective synchronisation of ovulation. The use of our new oocyte maturation classification may positively influence the effectiveness of Eurasian perch production.

Pore-scale investigation of immiscible displacement process in porous media under high-frequency sound waves

Although experimental and theoretical studies have been performed to identify the effects of elastic waves on multi-phase flow in porous structures, the literature lacks finely tuned experiments at the micro-scale. This paper reports observations and critical analysis of immiscible displacement in micro-scale porous media under ultrasonic energy. A number of experiments are performed on homogeneous and heterogeneous micromodels for varying wave frequency and power, initial water saturation, wettability and injection rates. We show that ultrasonic radiation influences the displacement pattern and yields lower residual non-wetting phase (oil) behind when low injection rates are applied. Higher wave frequency results in faster recovery of oil, but the ultimate recovery is controlled mainly by wave intensity. The presence of initial water saturation has a positive effect on the displacement, especially in an oil-wet medium. Of the possible mechanisms suggested for recovery enhancement under ultrasonic radiation, deformation of pore walls and change in fluid properties due to heating are not an issue in these experiments but other mechanisms including coalescence of oil droplets under oscillation, reduction of wetting films, adherence to grains and the peristaltic movement of fluids due to mechanical vibration were observed to be effective and are discussed in the analysis of the visual observations.

A new classification of pre-ovulatory oocyte maturation stages in pikeperch, Sander lucioperca (L.), and its application during artificial reproduction

This study aimed at improving the reproduction effectiveness and synchronization of ovulation in the pikeperch, Sander lucioperca (L.), during induced spawning, which is one of the main bottlenecks in the aquaculture of this species. For this purpose, a new categorization of maturation stages in pre-ovulatory oocytes was applied. It is generally based on two morphological indicators: germinal vesicle migration or its breakdown (GVBD) and different oil droplet coalescence rates. This categorization covered seven stages (from I to VII) – from the end of vitellogenesis to ovulation. The categorization was verified by controlled reproduction with the use of hormonal stimulation (500 IU of hCG per kg of female body weight) and low spawning temperature (12 °C), which extended the latency time. In addition, some morphological indicators (pseudo-gonadosomatic index, Fulton's condition coefficient) of females were calculated in order to determine their usability in determining the maturation stage. However, these indicators proved to be ineffective for this purpose, further highlighting the need to determine the maturational stages in pre-ovulatory oocytes to synchronize ovulation in pikeperch. During the experiment, ovulation seemed to be synchronized among the experimental treatments. Statistical differences were found in terms of latency time between experimental groups at different maturity stages (II – 78–98 h; III – 57–78 h; IV – 48–58 h; V – 32–49 h; VI – 5–30 h) according to the proposed classification. This classification and the results presented in the study significantly improved the synchronization of ovulation, which may positively affect the effectiveness of pikeperch production under controlled conditions.

Utilizing superhydrophilic materials to manipulate oil droplets arbitrarily in water

A facile method utilizing superhydrophilic materials to manipulate oil droplets freely in water is provided in this study. Due to the hydrophilic property and hierarchical structures of frosted glass plates, water was trapped in the interstices of glass microstructures. Trapped water served as supporting points to effectively prevent the penetration of oil droplets, yielding superoleophobic and low-adhesive surfaces in water. Then, oil droplets, whether heavier or lighter than water, could be manipulated arbitrarily by a pair of tweezers consisting of superoleophobic glass surfaces on the tips. This study successfully overcame adhesive problems in conventional oil droplet manipulation techniques. Besides freely on-demand manipulation of oil droplets, the coalescence of oil droplets containing different reagents led to miniature organic reactions happening inside such an oil-droplet-based miniature reactor. Most importantly, reaction products inside coalesced droplets could be collected effectively due to the ultra-low adhesive property of superoleophobic pedestals, which will be beneficial for harvesting valuable products in limited amounts. These results proposed a novel, fluoride-free and low-cost strategy for on-demand manipulation of oil droplets, which might provoke new ideas for controllable droplet motion and the design of miniature reactors.

The influence of interfacial ageing and temperature on the coalescence of oil droplets in water

Understanding the coalescence behaviour of two single droplets of industrial kerosene oil is an important precursor for predicting the stability of a concentrated kerosene emulsion system. In taking such an approach, distinct differences in the dynamic coalescence of fresh and aged binary droplets of analytical and technical grade kerosene was observed which we believe to be important with regard to the stability of concentrated systems. It was shown from induction time measurements (the time from first contact to rupture of the thin film separating the droplets) that the analytical grade kerosene binary droplets are considerable more stable than the technical grade at higher temperature (up to 65°C) but the analytical grade shows a gradual decrease in stability up to 65°C. At 75°C, both grades of kerosene droplets remained stable to coalescence. After this initial rupture, coalescence proceeded as a series of dynamic oscillations and further insight into the fusion behaviour could be obtained by analysis of the change in the surface area of the aggregated droplets as a function of time. The longer induction times correlated with the more vigorous post rupture oscillations (less damping resulting from an increase in interfacial elasticity) which were recorded during the drop fusion. These experiments reveal preliminary steps in the coalescence of oil droplets where measurements from first contact to final damped equilibrium are quantified. This aspect of coalescence has not been well represented in the earlier literature.

Effect of Electric Double Layer Repulsion on Oil Droplet Coalescence Process

AbstractFilm drainage between two droplets approaching each other at constant velocity under the influence of electric double layer repulsion is studied systematically. Based on the lubrication equations, a mathematical model is given to govern the evolution of film drainage between two oil droplets. This model consists of three coupled fourth‐order nonlinear parabolic partial differential equations describing the dynamic evolution of the film thickness, film pressure and surfactant interfacial concentration. The numerical method used is the finite element method. The main objective of this research work is to modify the film pressure equation by considering the electric double layer repulsion. The effects of electric double layer repulsion and viscosity ratio on film drainage are investigated theoretically.

Aggregation and Coalescence of Oil Droplets in Water via Electrohydrodynamic Flows

Electrohydrodynamic (EHD) flows are known to cause rigid colloids to aggregate near electrodes. Here we report that EHD flows also induce immiscible oil droplets to aggregate and, for sufficiently strong field strengths, to coalesce. We measure the aggregation and coalescence rates of micrometer-scale oil droplets in water, and we find that the most effective way to induce coalescence is by suddenly decreasing the applied frequency. We interpret the results in terms of a balance between EHD flow and colloidal forces, and we discuss the implications for using EHD flows to separate trace oils from solution.

Nano-emulsions prepared by the phase inversion composition method: Preparation variables and scale up

The aim of this work is to study, through experimental design, the effect of vessel geometry and scale-up in the properties of nano-emulsions prepared through the phase inversion composition method (PIC). Results show that a proper mixing is crucial for small droplet-sized nano-emulsions, especially when remaining free oil is found together with the key liquid crystal phase formed during the emulsification process. In these cases, mixing must be near the perfect mixed model. Proper geometries must be selected to promote a good mixture. Small addition rates V ad and high mixing rates ω promote the necessary mixing level. However, results indicate that, if free oil remains together with liquid crystal formed during emulsification, a too high ω could promote coalescence of oil droplets. When a cubic liquid crystal phase Pm3n is formed instead during emulsification, without free oil, coalescence is not promoted, probably due to the extremely high viscosity. For the system where Pm3n is formed during emulsification, scale-up cannot be done, as it would be expected, maintaining adimensional variables – Reynolds, Re, and adimensional time. A perfect correspondence between scales is observed when the total addition time and the lineal mixing rate are maintained between scales instead. Re, i.e. the ratio between inertial and viscous forces, does not seem adequate to describe the system, as inertial forces are worthless due to the extremely high viscosity.

Chickpea protein isolates obtained by wet extraction as emulsifying agents

Wet extraction of protein from defatted chickpea (variety Thiva (T), Greece) flour, at alkaline or slightly acidic pH, followed by isoelectric precipitation (pI) or ultrafiltration (UF) to recover the protein, was employed to obtain a number of chickpea protein isolates, enriched either in protein constituents belonging to the globulin (TpI, TUF, TUFG) or to the albumin fraction (TUFA). The interfacial activity and film-forming ability of the isolate protein constituents as well as their emulsifying properties were evaluated. The method applied for chickpea protein isolate preparation influenced to an appreciable extent their composition, adsorption behaviour to oil-water interfaces and emulsion formation and stabilization characteristics, especially with respect to oil droplet flocculation and coalescence. The isolates also differed in their ability to stabilize emulsions subjected to thermal processing or following storage under freezing conditions. The results are discussed in terms of compositional and, possibly, structural differences existing between the protein constituents of the chickpea isolates that may influence their functional behaviour in emulsion systems. The method applied for isolate preparation influenced to an appreciable extent the ability of proteins to adsorb to the oil-water interface and stabilize emulsions during long-time ageing or following heat treatment or freezing.

Macroporous Polymer from Core−Shell Particle-Stabilized Pickering Emulsions

Poly(styrene-co-N-isopropylacrylamide) (PS-co-PNIPAM) core-shell particles were synthesized and used as particulate emulsifiers in the preparation of particle-stabilized (Pickering) emulsions. Highly concentrated oil-in-water emulsions with an internal phase up to 80 vol % can be produced using PS-co-PNIPAM core-shell particles along as the emulsifiers in emulsions. The core-shell particles are adsorbed at the liquid interface, acting as a barrier against oil droplet coalescence. In addition, it is likely that excess particles simultaneously form a gel in the continuous phase to trap oil droplets in the gel matrix, in turn inhibiting creaming and phase inversion. Evaporation in air of such a core-shell particle-stabilized emulsion directly leads to porous membranes in the absence of chemical reactions. The pore walls of the final structures are densely packed with layers of the core-shell particles. This provides great flexibility to prepare functionalized porous materials for opening up new applications.

Mechanisms of Aqueous Extraction of Soybean Oil

Aqueous extraction processing (AEP) of soy is a promising green alternative to hexane extraction processing. To improve AEP oil yields, experiments were conducted to probe the mechanisms of oil release. Microscopy of extruded soy before and after extraction with and without protease indicated that unextracted oil is sequestered in an insoluble matrix of denatured protein and is released by proteolytic digestion of this matrix. In flour from flake, unextracted oil is contained as intact oil bodies in undisrupted cells, or as coalesced oil droplets too large to pass out of the disrupted cellular matrix. Our results suggest that emulsification is an important extraction mechanism that reduces the size of these droplets and increases yield. Protease and SDS were both successful in increasing extraction yields. We propose that this is because they disrupt a viscoelastic protein film at the droplet interface, facilitating droplet disruption. An extraction model based on oil droplet coalescence and the formation of a viscoelastic film was able to fit kinetic extraction data well.

Application of thermal treatments to enhance gel strength and stability of highly concentrated crayfish-based emulsions

Highly concentrated oil-in-water (O/W; 25:75 wt%) emulsions stabilized by crayfish flour (CF) have been subjected to thermal treatments in order to study potential enhancements on gel strength of the network structures formed among oil droplets, involving adsorbed and non-adsorbed protein segments. Application of in situ thermal treatments, monitored by Small Amplitude Oscillatory Shear (SAOS), may lead to remarkable changes in the gel strength of CF-based emulsions, depending on processing conditions. If the heating temperature is above a critical value, the exposition time being long enough, thermal energy eventually leads to coalescence of oil droplets and subsequent emulsion destabilization. This behaviour has been confirmed by Droplet Size Distribution (DSD) measurements. The pH exerts a strong influence on the evolution of viscoelastic moduli. Little changes are produced at alkaline conditions, whereas a noticeable enhancement is apparent at neutral and acid pH. Application of consecutive double thermal cycle confirms the reversibility of the reinforcement induced by the cooling stage. The results may be explained in terms of the balance between electrostatic forces (predominant at alkaline pH) and hydrophobic interactions that favour protein aggregation and crosslinking (over heating stages), as well as hydrogen bonding (at the cooling stage). In addition, the influence of gel strength enhancement on the subsequent improvement of emulsion stability has been investigated by applying thermal treatments in a thermostatic bath. A clear enhancement in emulsion stability is achieved by these thermal treatments, although its contribution is not enough to produce long-term stability and a combination with other stabilizing strategies should be developed.

Recovery of linseed oil dispersed within an oil-in-water emulsion using hydrophilic membrane by rotating disk filtration system

The purpose of this paper is to investigate a method to recover the linseed oil from oil-in-water (O/W) emulsion by a rotating disk filtration system. The influence of transmembrane pressure (TMP), disk rotating speed, and disk geometry on permeate flux and oil recovery has been studied. Hydrophilic polyvinylidene difluoride (PVDF) membranes with average pore size 0.15 μm and polyethersulfone (PES) membranes with 50 kDa molecular weight cut off (MWCO) were used. The results showed that the rotating disk module can produce high permeate fluxes. The highest permeate fluxes were obtained when using a rotating disk equipped with vanes, which generated the largest shear rates at the membrane. This study demonstrated that hydrophilic membranes were suitable for demulsification of linseed oil-in-water emulsion. The linseed oil droplets in the emulsions could be separated by concentration tests due to the coalescence of oil droplets in the concentration polarization layer. For an initial oil mass of 46.5 g, 35.2 g supernatant oil was obtained owing to oil droplets coalescence. This supernatant oil represented a recovery of 76%. The rotating disk with vanes consumed less specific energy than smooth disk in the concentration tests.

Formation and consolidation of filter cake in microfiltration of emulsion–slurry

The dynamic behaviors of unstirred dead-end microfiltration were explored under constant pressure conditions using a binary dispersion of oil-in-water (O/W) emulsion and polymethyl-methacrylate (PMMA) slurry, which is referred to as emulsion–slurry. The Ruth filtration coefficient determined from the flux decline data increased steadily during the course of filtration, and then a bilayer filter cake formed composed of the upper emulsion cake and the lower PMMA cake. Each average specific filtration resistance of the emulsion cake and the PMMA cake was well evaluated in terms of the resistance-in-series model in filtration. The PMMA cake was nearly incompressible, while the emulsion cake formed on the PMMA cake was highly compressible. Only the emulsion cake was consolidated without the cake cracking or the coalescence of oil droplets. The compressed cake of gel–emulsion had a porosity that was much lower than that of hexagonal close packing of undistorted spheres because of the remarkable deformation of oil droplets under the action of the compressive pressure. It was clearly demonstrated that the gel–emulsion cake formed in filtration of emulsion–slurry was exactly similar in nature to that formed in filtration of mono-dispersed O/W emulsion.

Heterogeneous hydrodynamic coagulator-coalescer devices

The kinetics of heterogeneous hydrodynamic coagulation and coalescence of motor oil droplets 0.4–1.5 μm in size with a concentration of 0.15–0.5 vol % is investigated in a convoluted tube, a centrifugal pump, and their combination. Kinetic parameters of the coagulation-coalescence process, which proceeds hundreds times faster than sedimentation, are determined.

A study of oil droplet coalescence

Oil droplets dispersed in water can be readily studied when they are coated with surfactants, which lower their interfacial tension and enhance their stability. Pure oil droplets are more difficult to study because of their high interfacial tension, which facilitates coalescence and the adsorption of contaminants. In this study, we have characterised the surface charging properties of a water insoluble oil, bromododecane, which has a density close to water. The small density difference allows us to study relatively large drops of this oil and to analyse its coalescence behaviour. The results obtained with this simple, surfactant-free, system suggest that an additional attractive force, such as the long range hydrophobic interaction, might be required to explain oil droplet coalescence behaviour.