Emulsion Droplet Size Distribution Research Articles

Estimating droplet size distribution of emulsions using turbidity measurements: A soft sensor based on artificial neural network

Ability to characterise droplet size distribution (DSD) of emulsions in real-time is essential for on-demand production of customised emulsions. In this work, for the first time, we demonstrate a possibility of estimating full DSD of oil in water emulsions from turbidity measurements using a single wavelength light source. We used recently published data of DSD and turbidity measurements of rapeseed oil in water emulsions (oil volume fractions of 0.15, 0.3 and 0.45) produced with vortex based hydrodynamic cavitation device. Measured DSDs are represented by weighted sum of three log-normal distributions. We developed an approach and a methodology based on artificial neural network (ANN) to estimate DSD from a single measurement of turbidity. A mathematical model is developed to simulate measured turbidity profiles using the known DSDs. The validated model was then used to generate simulated data of turbidity and oil volume fraction pairs (105 pairs). This synthetic data was used to train ANN which used turbidity and volume fraction as input and eight parameters of DSD as output. The developed ANN was able to capture the experimentally measured characteristic diameters and DSDs very well for three oil volume fractions and four different number of passes. The presented methodology and results will be useful for developing an in-line soft sensor based on turbidity measurements for real time estimation of full DSDs of emulsions.

Droplet Size Distribution in Emulsions.

The droplet size in emulsions is known to affect the rheological properties and plays a crucial role in many applications of emulsions. Despite its importance, the underlying mechanisms governing droplet size in emulsification remain poorly understood. We investigate the average drop size and size distribution upon emulsification with a high-shear mixer for model oil-in-water emulsions stabilized by a surfactant. The size distribution is found to be a log-normal distribution resulting from the repetitive random breakup of drops. High-shear emulsification, the usual way of making emulsions, is therefore found to be very different from turbulent emulsification given by the Kolmogorov-Hinze theory, for which power-law distributions of the drop size are expected. In agreement with this, the mean droplet size does not follow a scaling with the Reynolds number of the emulsification flow but rather a capillary number scaling based on the viscosity of the continuous phase.

Design of vortex-based cavitation devices/reactors: Influence of aspect ratio, number of inlets and shape

Vortex-based hydrodynamic cavitation devices are being used in a wide range of applications. However, adequate information on the design of such devices is not available. In this work, we have computationally investigated the influence of key design parameters such as the aspect ratio of the vortex chamber, the number of tangential inlets and the shape of the device on resulting flow characteristics and cavitation. Experiments were carried out to validate key findings from the computational studies. These investigations revealed that the aspect ratio of the vortex chamber as six may be considered as optimum. The performance of single and multiple inlet devices was found to be comparable at the same pressure drop (that is at same energy consumption per m3). Scale-up with a geometric similarity led to a reduction in the extent of cavitation for same energy consumption per m3. For facilitating scale-out option, an attempt was made to simplify the configuration of the vortex-based cavitation device. Computational results indicated that the cavitation performance of simplified configuration was not significantly inferior. A case of the formation of liquid–liquid emulsion was taken as a test case for evaluation of a modified cavitation device based on the present investigations. The droplet size distributions of emulsions generated by both the devices indicate that the proposed simplified configuration, which may facilitate fabrication and offer integrated scale-out options, performs almost at par with a complex configuration. The presented results will be useful for optimising designs of vortex-based hydrodynamic cavitation devices/ reactors.

Effect of ionic types on the characteristics of Pickering emulsions stabilized by myofibrillar proteins from hairtail (Trichiurus lepturus)

Ion is an important factor to affect the characteristics of protein-based Pickering emulsions. However, the effect of ionic types on the characteristics of Pickering emulsions prepared by myofibrillar proteins (MPs) from hairtail (Trichiurus lepturus) is still unclear. Therefore, the characteristics of Pickering emulsions stabilized by MPs (MPPEs) at different metal ions (Na+, K+, Mg2+, Ca2+) were investigated. MPPEs at Na+ and K+ possessed high absolute values of Zeta potential, small particle size and uniform distribution of emulsion droplets compared to that at Mg2+ and Ca2+. After heat treatment, the particle size of MPPEs at Na+ and K+ had no significant change with high stability compared to that at Mg2+ and Ca2+. MPPEs at Na+ and K+ exhibited gel-like behavior and relatively stable compared with those at bivalent ions (Mg2+ and Ca2+). This study may be helpful for the high-value utilization of fish proteins in constructing emulsion systems.

Cinnamon essential oil Pickering emulsions: Stabilization by bacterial cellulose nanofibrils and applications for active packaging films

Pickering emulsions are emulsions stabilized by solid particles with a wide range of potential applications as they typically provide more stable systems than surface-stabilized emulsions. Among the various solid stabilizers, bacterial cellulose (BC) may open up new opportunities for future Pickering emulsions due to its unique nano-size, amphiphilicity and other excellent properties. In this study, BC, TEMPO-oxidized BC (TOBC) and dialdehyde cellulose (DAC) were used as emulsifiers to stabilize cinnamon essential oil (CEO) Pickering emulsions. The microstructure, oil droplet size distribution, storage and loss moduli of the Pickering emulsions were affected by the type of emulsifier used. Compared to BC and DAC nanofibers, TOBC nanofibers exhibited better emulsifying capacity. TOBC (1%)-stabilized Pickering emulsion showed smaller droplet size, narrower size distributions, better stability and sustained release ability. Moreover, the Pickering emulsions showed high antibacterial activities against Gram-positive bacteria S. aureus and Gram-negative bacteria E. coli. Active gelatin composite films containing TOBC (1%)-stabilized CEO Pickering emulsions were successfully fabricated and showed good antibacterial and antioxidant properties, which make them suitable for food packaging application.

EVOLUTION OF THE DISTRIBUTION FUNCTION OF DROPS IN AN OIL EMULSION

Oil emulsions are polydisperse media and have a droplet size in the macro and micro range. Macro and microemulsions can be found in both water-in-oil emulsion types and oil-in-water emulsion types. Taking into account the size distribution of water-oil emulsion droplets has a great influence on the accuracy of calculations when modeling the process of oil dehydration. Droplet size and droplet size distribution are important for the stability and viscosity properties of the emulsion. In the article, based on the rate of coalescence and fragmentation of particles, an expression is proposed for the rate of change in the number and size of particles per unit volume. On the basis of the Fokker-Planck equation, an expression for the distribution function of water droplets in an oil emulsion is found and, on its basis, an estimate of the distribution is investigated

Design of vitamin-loaded emulsions in agar hydrogel matrix dispersed with plant surfactants

Polysaccharide colloids and gels supplemented with bioactive compounds are very common in the food industry, although hydrophobic substances can significantly affect the structure and physicochemical properties of hydrogels. In the present study, the impact of natural surfactants, saponins, on agar hydrogels containing vitamins A and E was evaluated. The study started with the research of droplet size distribution of vitamin-loaded aqueous emulsions, stabilized by saponins. A composition containing vitamins at a concentration of 2 mg mL−1 and Sapindus mukorossi saponins at a concentration of 0.1 mg mL−1 was used for further analysis. The second stage of our studies includes the introduction of the emulsion into a hydrogel matrix based on agar. The vitamin-containing hydrogel systems obtained were studied to verify how the vitamin, saponin, and agar concentration affect the mechanical and swelling properties of the materials, as well as their color and transparency. An important aspect was to indicate how the presence of vitamins affects the activity of water molecules measured by low-field NMR. The collected results indicated that, as a result of the use of saponins, stable emulsions that can be incorporated into hydrogels can be obtained while the size and properties of the droplets are maintained without changing their physicochemical properties.

Emulsification mechanism in an ultrasonic microreactor: Influence of surface roughness and ultrasound frequency

An ultrasonic microreactor with rough microchannels is presented in this study for oil-in-water (O/W) emulsion generation. Previous accounts have shown that surface pits or imperfections localize and enhance cavitation activity. In this study cavitation bubbles are localized on the rough microchannels of a borosilicate glass microreactor. The cavitation bubbles in the microchannel are primarily responsible for emulsification in the ultrasonic microreactor. We investigate the emulsification mechanism in the rough microchannels employing high-speed imaging to reveal the different emulsification modes influenced by the size and oscillation intensity of the cavitation bubbles. The effect of emulsification modes on the O/W emulsion droplet size distribution for different surface roughness and frequency is demonstrated. The positive effect of the frequency on minimizing the droplet size utilizing a reactor with large pits is presented. We also demonstrate microreactor systems for a successful generation of miniemulsions with high dispersed phase volume fractions up to 20%. The observed emulsification mechanism in the rough microchannel offers new insights into the utility and scale-up of ultrasonic microreactors for emulsification.

Experimental Study and Numerical Simulation of W/O Emulsion in Developing Heavy Oil Reservoirs

In the process of waterflooding development of heavy oil, W/O emulsion has a strong ability to improve the mobility ratio and block the high-permeability layer, which can effectively improve the sweep coefficient and enhance oil recovery. In this paper, the stability and droplet size distribution of emulsions under different conditions were studied by taking heavy oil and formation water from Jimusar Oilfield in Xinjiang as samples. On this basis, double-pipe core flooding experiments were carried out to study the shut-off ability and oil displacement efficiency of W/O emulsion, and then a numerical simulation was carried out. The results show that oil and water can be completely emulsified when the stirring speed is higher than 4000 r/min. A stable emulsion can be formed when the experimental temperature is lower than 60 °C. A lower water cut results in a more stable emulsion. The emulsion is difficult to stabilize after the salinity exceeds 10,000 mg/L. When the pH value is about 7, the stability of the emulsion is the worst. With the increase in stirring speed, the increase in temperature, and the decrease in water content and salinity, the emulsion droplet size range is relatively concentrated, and the average particle size is smaller. In heterogeneous reservoirs, the permeability of different percolation channels is quite different, such that the displacement fluid only percolates along the high-permeability channel and cannot drive oil effectively. The results of displacement experiments show that the emulsion with a water cut of 60% has high viscosity and obvious sweep ability, but its stability is very poor; the effect is opposite when the water cut is less than 40%. The shut-off ability of W/O emulsion disappears gradually when the permeability contrast is more than 5.92. The research results are of great significance for improving oil recovery in heterogeneous heavy oil reservoirs.

Cellulose nanofiber from pomelo spongy tissue as a novel particle stabilizer for Pickering emulsion

For the high-value utilization of agricultural wastes to promote sustainable development, in this work, pomelo spongy tissue cellulose nanofibers (PCNFs) with lengths >3 μm and widths 33–64 nm were prepared by high pressure homogenization (HPH). The PCNFs were used to stabilized Pickering emulsion, and the emulsion with oil phase fraction in the range of 10 % to 50 % (w/w) exhibited outstanding stability. The increase in PCNFs concentration also enhanced the three-dimensional network structure, resulting in higher stability of the emulsion. Moreover, the droplet size distribution of emulsion would be greatly improved by moderate heating. No creaming was observed in emulsions over a wide range of ionic strengths (20–200 mM) after storage for 30 d. And the excellent emulsifying properties of the PCNFs were mainly attributed to their adsorption at the oil-water interface and the formation of a three-dimensional network structure. All the results indicated that the PCNF would be a promising novel stabilizer for Pickering emulsions.

A fungal cellulose nanocrystals-based approach to improve the stability of triterpenes loaded Pickering emulsion

Depolysaccharide residues of edible fungus Pleurotus eryngii (dePSR-Pe), a mushroom industry waste, have abundant cellulose. In this study, the cellulose nanocrystals of P. eryngii (PeCNs) were extracted by hydrochloric acid. Results showed that the length of PeCNs is 469 ± 76.41 nm with a high aspect ratio of 40–100 and needle morphology. The structural characterization revealed that PeCNs had good thermal stability (approach 300 °C) and high crystallinity (84.2 %). An O/W Pickering emulsion stabilized with PeCNs was prepared to inhibit lipid oxidation and improve the loading capacity of triterpenes of P. coco. Unimodal size distribution of emulsion droplets was obtained under an optimized aqueous-phase condition to form a metastable emulsion, regardless of varying oil-water volume ratio <50/50. In vitro digestion study suggested that triterpenes-loaded Pickering emulsion had 1–3 times higher drug stability than bulk oil. These metastable Pickering emulsions call for fewer nanoparticles and provide a new strategy for the industry application of cellulose nanocrystals at less cost.

Optimization of Pea Protein Isolate-Stabilized Oil-in-Water Ultra-Nanoemulsions by Response Surface Methodology and the Effect of Electrolytes on Optimized Nanoemulsions

Nanoemulsions are optically transparent and offer good stability, bioavailability, and control over the targeted delivery and release of lipophilic active components. In this study, pea protein isolate (PPI)-stabilized O/W nanoemulsions were evaluated using response surface methodology to obtain optimized ultra-nanoemulsions of Sauter mean diameter (D3,2) &lt; 100 nm using a high-pressure homogenizer (HPH). Furthermore, the effect of food matrix electrolytes, i.e., the pH and ionic strength, on the emulsion (prepared at optimized conditions) was investigated. The results revealed that the droplet size distribution of emulsions was mainly influenced by the PPI concentration and the interaction of oil concentration and HPH pressure. Moreover, a non-significant increase in droplet size was observed when the nanoemulsions (having an initial D3,2 &lt; 100 nm) were stored at 4 °C for 7 days. Based on the current experimental design, nanoemulsions with a droplet size &lt; 100 nm can effectively be prepared with a high PPI concentration (6.35%), with less oil (1.95%), and at high HPH pressure (46.82 MPa). Such emulsions were capable of maintaining a droplet size below 100 nm even at ionic conditions of up to 400 mM NaCl and at acidic pH.

Factors Influencing the Droplet Size of Asphalt Emulsion during Fabrication

The size distribution of asphalt droplets greatly affects the overall technical properties of asphalt emulsion, while it did not obtain much concern previously. In order to fabricate a good-quality asphalt emulsion with a small droplet size distribution, the effect of preparation parameters on the asphalt droplet size distribution, such as emulsifier dosage, asphalt temperature, shear time, pH value, and soap solution temperature, were systematically studied. All preparation parameters can affect the droplet size distribution of asphalt emulsion as well as the representative droplet diameters for the 10th, 50th and 90th cumulative volume percentile (D10, D50, and D90). The order of preparation parameters are ranked as: emulsifier dosage &gt; temperature of soap solution &gt; pH of soap solution &gt; shear time &gt; asphalt temperature. Therefore, the emulsifier dosage, the temperature and pH of the soap solution should be carefully controlled to obtain asphalt emulsion with good droplet size distribution during fabrication. Compared to D10, the D50 and D90 are more easily affected by the fluctuant preparation parameters, which are recommended to be utilized to evaluate the emulsifying effect of asphalt emulsion and judge the asphalt droplet size distribution.

A study of alkali-silica nanoparticle-polymer (ANP) flooding for enhancing heavy oil recovery

The method of nanofluid flooding to enhance heavy oil recovery has attracted much attention in oilfields. An EOR technology named alkali-silica nanoparticle-polymer (ANP) flooding was designed to enhance heavy oil recovery. The performance of the ANP flood system on reducing interfacial tension (IFT), altering the wettability of rock surface, emulsifying and displacing heavy oil were compared with that of polymer (P), alkali-polymer (AP) and nanoparticle-polymer (NP) flood systems. Visual flooding test was conducted to investigate the displacement mechanisms of different flood systems in porous media. ANP nanofluid could remain stable over 30 days without sedimentation of nanoparticles. The emulsifying ability of the four flood systems for heavy oil followed the order: P < NP < AP < ANP. Based on the analysis of droplet size distribution of emulsion and changes of IFT value with alkali concentration, the best formula of ANP system to emulsify heavy oil was 0.3% [w/v] Na2CO3 + 0.1% [w/v] silica nanoparticle + 1000 mg L−1 polymer. Electrostatic repulsion between silica nanoparticles and oil droplets played a dominated role on stabling ANP emulsion. ANP flood system could change the wettability of rock surface to a more water-wet state (contact angle varied from 85.4° to 35.6°). Core and visual flooding tests proved that ANP flood system had a better sweep and displacement efficiency for heavy oil than other three flood systems (P, AP and NP), which could enhance heavy oil recovery by 21.19% after water flooding in a sandstone core. Emulsification is the main mechanism for ANP flooding to enhance heavy oil recovery.

Microscopy-Assisted Digital Image Analysis with Trainable Weka Segmentation (TWS) for Emulsion Droplet Size Determination

The size distribution of droplets in emulsions is very important for adjusting the effects of many indices on their quality. In addition to other methods for the determination of the size distribution of droplets, the usage of machine learning during microscopic analyses can enhance the reliability of the measurements and decrease the measurement cost at the same time. Considering its role in emulsion characteristics, in this study, the droplet size distributions of emulsions prepared with different oil/water phase ratios and homogenization times were measured with both a microscopy-assisted digital image analysis technique and a well-known laser diffraction method. The relationships between the droplet size and the physical properties of emulsions (turbidity and viscosity) were also investigated. The results showed that microscopic measurements yielded slightly higher values for the D(90), D[3,2], and D[4,3] of emulsions compared to the laser diffraction method for all oil/water phase ratios. When using this method, the droplet size had a meaningful correlation with the turbidity and viscosity values of emulsions at different oil/water phase ratios. From this point of view, the usage of the optical microscopy method with machine learning can be useful for the determination of the size distribution in emulsions.

Influence of the droplet trajectory on the resulting droplet deformation and droplet size distribution in high‐pressure homogenizer orifices

AbstractHigh‐pressure homogenization is a commonly used process to produce emulsions with a droplet size of less than 1 μm. During the process, a pre‐emulsion is pumped with a pressure of several mega Pascal through a disruption unit, where the droplets are deformed and subsequently broken up in the turbulent area of the disruption unit. The scope of this investigation is to determine the influence of the droplet trajectory on the droplet size distribution of emulsions of different viscosity ratios or interfacial tension. Measurements of the droplet deformation prior to the droplet breakup using image‐processing tools complemented the observations. In addition, computational fluid dynamics simulations were performed to determine the stress history on the droplet trajectories. It was found that droplets on a trajectory close to the wall are more deformed when leaving the disruption unit compared to droplets on the centreline. The deformation of droplets at the edge of the jet increases downstream the disruption unit until it is finally disrupted. The simulation results support the experimental data, as it can be shown that shear and strain stresses on the trajectories close to the wall significantly exceed the stresses on the trajectories on the centreline. For an emulsion with a viscosity ratio greater than 3, droplets on a trajectory close to the wall resulted in smaller droplets and narrower droplet size distribution, while no significant influence was found for smaller viscosity ratios. Lowering the interfacial tension results in a stronger deformation, which was more pronounced for lower viscosity ratios (λ ≈ 3).

Oil Droplet Coalescence in W/O/W Double Emulsions Examined in Models from Micrometer- to Millimeter-Sized Droplets

Water-in-oil-in-water (W1/O/W2) double emulsions must resist W1–W1, O–O and W1–W2 coalescence to be suitable for applications. This work isolates the stability of the oil droplets in a double emulsion, focusing on the impact of the concentration of the hydrophilic surfactant. The stability against coalescence was measured on droplets ranging in size from millimeters to micrometers, evaluating three different measurement methods. The time between the contact and coalescence of millimeter-sized droplets at a planar interface was compared to the number of coalescence events in a microfluidic emulsion and to the change in the droplet size distributions of micrometer-sized single and double emulsions. For the examined formulations, the same stability trends were found in all three droplet sizes. When the concentration of the hydrophilic surfactant is reduced drastically, lipophilic surfactants can help to increase the oil droplets’ stability against coalescence. This article also provides recommendations as to which purpose each of the model experiments is suited and discusses advantages and limitations compared to previous research carried out directly on double emulsions.

Effect of water chemistry on the stability of water-in-crude oil emulsion: Role of aqueous ions and underlying mechanisms

Recent studies have shown that although low salinity waterflooding leads to promising EOR impacts, it is to blame for the formation of unwanted water-in-oil emulsions. Thus, this study aims to explore the effect of water chemistry, namely ionic strength and ion types on the stability of natural water-in-oil (W/O) emulsions at the reservoir temperature of 80 °C. To this end, seawater and its dilutions with different concentrations of potential determining ions (PDIs) were used as the aqueous phase. The experimental study was performed by tracking the emulsion droplet size distribution, phase separation study and also IFT measurements. Results showed that the higher the ionic strength of the aqueous phase, the lower the W/O emulsion stability, which could be explained based on the salting-out mechanism. It was found that the IFT parameter did not significantly contribute to the emulsion stability. Regarding the effect of ion types on the stability of emulsions prepared by eight-time diluted seawater with different PDIs, the trend was Mg2+≥ Ca2+> SO42−. These observations were described in the light of the higher tendency of divalent cations to bond with crude oil polar components. As to the phase separation study, the amount of expelled water in the presence of Mg2+ was 15 vol% of the initial water, compared to 24 vol% for Ca2+ and almost half for SO42− after one-day aging. It was also found that the co-existence of sulfate with divalent cations improved the emulsion stability, while the less stable emulsions were obtained by the sulfate-rich brine. This was further supported by the droplet size distribution profile in which a more uniform profile was obtained for emulsions with the co-existence of sulfate and divalent cations as compared to the sulfate-rich samples. Results of this study addressed that the ionic strength of the aqueous phase coupled with its ionic content regulates the emulsion stability, such that there exists a specific range of salinity and ion concentration beyond that the emulsion stability may impair.

Towards an accurate size distribution of emulsion droplets by merging distributions estimated from different measuring methods

It is well known that the use of different methods for measuring particle size distributions may lead to very different results. This is completely understood in the case of solid particles which may differ in several other aspects beyond their size (e.g. shape). However, the explanation is more difficult for the case of small size emulsion droplets where the shape of all droplets is spherical. Here, the idea that the error distribution with respect to droplet size is the origin of different results from different measuring method, is proposed. Each measuring method relies on a physical principle and so the error is relatively uniformly distributed through the values of the variable related to this physical principle. Any attempt to transform this variable leads to severe error maldistribution. The present work not only explains the reason of deviations of droplet size distribution between measuring methods but also suggests the compilation of information from two measuring methods to find a particle size distribution (PSD) with increased accuracy compared to the two individual methods. Several approaches in this direction are proposed and tested.

Determination of the pH- and thermal stability mechanism of lipophilic protein–hydroxypropyl methylcellulose oil-in-water emulsion

The aim of this study is to investigate the mechanism through which hydroxypropyl methylcellulose (HPMC) addition improves the stability of soybean lipoprotein (LP) under acidic conditions and the thermal stability of LP-HPMC emulsions. Results of SDS-PAGE, Raman spectroscopy, and X-ray diffraction studies reveal that the active sites of the LP-HPMC complexes varied with a change in pH and the amide III bands and the polarity of the microenvironment decrease with increasing HPMC content. The LP-HPMC complex does not form new subunits or crystals, but forms non-covalent bonds exploiting electrostatic and hydrophobic interactions. The addition of HPMC results in a change in the microstructure and droplet size distribution of LP-HPMC emulsions and an increase in the LP denaturation temperature; thus, the thermal stability of the emulsion decreases. This study can help develop non-heated emulsion delivery systems that remain stable in the gastric environment and promote the targeted release in the intestines.