Rheology Of Emulsions Research Articles

Microfluidic rheology of the multiple-emulsion globule transiting in a contraction tube through a boundary element method

Through a lately developed boundary element method, this paper investigates the rheology of the multiple-emulsion globule with various internal structures in a contraction tube. As fine templates to prepare microcapsules for targeted drug delivery, multiple emulsions (ME) with complex structures have been generated through microfluidics. The deformation and breakup of multiple emulsions in a microchannel are critical to the transport and release of their inclusion. However, the numerical investigation of the rheology of multiple emulsions in a contraction tube is only limited to a simple case, i.e., core-shell double emulsions (CSDE), currently. In this paper, the boundary element method is employed to investigate the deformation and displacement of 2-dimensional globules of three types of multiple emulsions, i.e., concentric ME with multiple layers, double emulsions containing multiple inner droplets and ME with asymmetric internal structures, in a contraction tube. Comparing to those of CSDE, the complication of internal structures and the collision among inner droplets will subject the globule to flows with higher pressure drops when the volume flow rates are fixed.

Light beam reflectance measurement of droplets diameter distribution in crude oil emulsions

Stable oil field emulsions create challenging conditions in the petroleum production industry. One important characteristic affecting the stability and rheology of emulsions is the Droplet Diameter Distribution (DDD). A few techniques are available to determine the DDD in clear and dark liquid/liquid mixtures. Most of them, like the traditional light scattering techniques, require sampling and dilution. Dilution can affect the droplets coalescence rate, and consequently, change the DDD by altering the solubility state of components responsible for emulsion interface properties. Moreover, the samples obtained may not be representative of the actual process conditions once depressurized to ambient for observation.Focused Beam Reflectance Measurements (FBRMs) were conducted on suspensions mimicking the optical properties of emulsion systems, with the goal of optimizing the instrumental settings. Then, the same technique was applied to water-in-crude oil and crude oil-in-water emulsions to evaluate its accuracy.An algorithm was developed to compute the diameter distribution in populations of spherical droplets from the chord length distributions measurement data.The greatest advantage of this technique is the ability to perform a real-time, in situ measurement of DDD at actual process conditions. The method is capable of repeatable measurements of droplet diameter distributions; however, the measurements are limited within a range of droplet sizes, and the results are sensitive to the relative optical properties of the continuous and dispersed phases, making the calibration step a fundamental phase of the measurement protocol.

Determination of the Real Influence of the Addition of Four Thickening Agents in Creams Using Rheological Measurements

This study aimed to characterize different emulsions obtained by the addition of four thickening agents, using rheological measurements, beyond analyzing the emulsions by polarized light microscopy looking for liquid crystals on them. The addition of these four thickening agents did not modify the base emulsion rheology, only an improvement in the sensory of the formulation was verified. The polarized light microscopy showed the formation of liquid crystalline structures in all the formulations, thus, the thickening agents did not influence in this parameter too. However, the emulsions could be considered appropriated for cosmetic purposes, probably being highly physically stable.

Emulsions stabilized with solid nanoparticles: Pickering emulsions

Pickering emulsions are attractive formulations because they are simple and bear strong similarities with the well-known surfactant-based emulsions. Pickering emulsions have been largely ignored since their early disclosure in 1907 and arouse a renewed interest quite recently. Since this unintelligible time gap raises suspicion, the first aim of the present review is giving the simple fundamental rules as an introduction for newcomers in the topic. The basic physical chemistry of Pickering emulsions is explained and the ways to control the parameters of higher relevance with respect to development of applications are given. This first part covers the choice of the solid nanoparticles used as stabilizers and their surface properties, the control of emulsion type, droplet size, and rheology. A second part gives examples of some applications in drug delivery and manufacturing of porous nanomaterials as illustrations of the potential of such emulsions.

Rheology of unstable mineral emulsions

In this paper, the rheology of mineral oils and their unstable water emulsion were investigated. The oil samples were domestic crude oil UA, its fractions UA1, UA4 and blend semi-product UP1, while the concentration of oil in water emulsions was in the range from 1 up to 30%. The results were analyzed based on shear stress. The oil samples UA, UA1 and UP1 are Newtonian fluids, while UA4 is pseudoplastic fluid. The samples UA and UA4 show higher value of shear stress (83.75 Pa, 297 Pa), then other two samples UA1 and UP1 (18.41 Pa, 17.52 Pa). Rheology of investigated oils due to its complex chemical composition should be analyzed as a simultaneous effect of all their components. Therefore, structural composition of the oils was determined, namely content of paraffins, naphthenes, aromatics and asphaltenes. All samples contain paraffins, naphthenes and aromatics but only oils UA and UA4 contain asphaltenes as well. All investigated emulsions except 30% EUA4 are Newtonian fluids. The EUA4 30% emulsion shows pseudoplastic behaviour, and it is the only 30% emulsion among investigated ones that achieves lower shear stress then its oil. The characteristics of oil samples that could have an influence on their properties and their emulsion rheology, were determined. These characteristics are: neutralization number, interfacial tension, dielectric constant, and emulsivity. Oil samples UA and UA4 have significantly higher values of neutralization number, dielectric constants, and emulsivity. The sample UA has the lowest value of interface tension and the greatest emulsivity, indicating that this oil, among all investigated, has the highest preference for building emulsion. This could be the reason why 20% and 30% emulsions of the oil UA achieve the highest shear stress among all investigated emulsions.

Stable emulsions with thermally responsive microstructure and rheology using poly(ethylene oxide) star polymers as emulsifiers

Poly(ethylene oxide) star polymers (PEO stars) were prepared by atom transfer radical polymerization of 2000 molecular weight PEO methacrylate macromonomer with divinylbenzene as a crosslinking co-monomer. With an average of 460arms per star, these PEO stars had a 12nm radius of gyration that is consistent with a dense polymer core surrounded by an extended PEO corona. The PEO stars were extremely efficient emulsifiers, stabilizing cyclohexane-in-water or xylene-in-water emulsions against coalescence for several months at aqueous phase concentrations as low as 0.008wt% or 0.01wt%, respectively. Consistent with their emulsifying performance, PEO star adsorption decreased interfacial tension by approximately 22mN/m and imparted significant dilatational elasticity to the xylene/water interface. PEO stars were thermally responsive, displaying a cloud point upon heating in water that was tuned by addition of kosmotropic electrolytes, and they in turn produced xylene-in-water emulsions that were thermally responsive in terms of the dispersion state of the emulsion droplets and the emulsion rheology. Emulsions prepared at room temperature mainly had non-flocculated droplets. Heating such an emulsion above the cloud point temperature triggered droplet flocculation, but not coalescence, that in turn was associated with increased viscous and elastic moduli of the emulsion measured after cooling back to room temperature. Emulsions that initially were homogenized above the cloud point temperature and then cooled showed neither droplet flocculation nor rheological thickening relative to emulsions that were prepared and held at room temperature. A mechanism based on the bridging behavior of PEO stars adsorbed at the droplet/water interface is postulated to explain this thermal response of the emulsion microstructure.

The effect of interfacial slip on the rheology of a dilute emulsion of drops for small capillary numbers

We present the constitutive equation for the volume-averaged hydrodynamic stress for a dilute emulsion in a linear ambient flow, when there is slip at the liquid-liquid interface between the Newtonian drop and the suspending fluids. Slip is modeled using a simple Navier slip boundary condition. We provide analytical solutions in the limit of small capillary numbers for the shape deformation, viscosity, and normal stresses. Slip moderates these quantities, with changes from the no-slip case being more pronounced for large viscosity ratios of the drop relative to the suspending fluid. It has been suggested in the past that slip can explain the anomalously low viscosities of certain polymeric blends. Our analysis indicates that slip can only partially account for these deviations, and that other mechanisms should be explored to explain the residual discrepancy.

Stability of water-in-crude oil emulsions: Effect of cocamide diethanolamine (DEA) and Span83

Water-in-oil emulsions are important in the petroleum industry in production operations, where the water content of the emulsion can be as high as 60% in volume. An environmentally friendly, nonionic emulsifying agent for crude oil emulsions Cocamide diethanolamine (Cocamide DEA) is introduced in the present work. The emulsion formation, rheology, stability and water separation performance of the DEA emulsifier was tested and compared with the commercially known Span83 non-ionic emulsifier. Water content (30, 40 and 50 vol.%), emulsifier molecular weight, emulsifier concentration (0.5, 1.0 and 1.5 vol.%) were the major variables investigated. The formulated emulsions viscosities and shear stress were measured at different operating temperatures (28 to 90°C) and different spindle rotation speeds (50 to 200). The experimental results showed that, for all the emulsion formed, the viscosity of the emulsion increases by increasing the water content and emulsifier concentration and decreases by increasing the rotation speed. The viscosity measurements were not constant with the spindle speed which confirms the non-Newtonian nature of the formulated emulsions. Finally, the experimental results showed that the emulsions formulated using the DEA emulsifier were more stable than the Span83 emulsions where the water separation time was longer and the water separation percentage was lower. Key words: Water in oil (w/o) emulsions, stability, surfactants, crude oil, diethanolamine (DEA).

Lactobionic acid as antioxidant and moisturizing active in alkyl polyglucoside‐based topical emulsions: the colloidal structure, stability and efficacy evaluation

Cosmeceutical antioxidants may protect the skin against oxidative injury, involved in the pathogenesis of many skin disorders. However, an unsuitable topical delivery system with compromising safety profile can affect the efficacy of an antioxidant active. This study investigated the antioxidant potential of lactobionic acid (LA), a newer cosmeceutical active, per se (in solution) and incorporated into natural alkyl polyglucoside (APG) emulsifier-based system using 1,1-diphenyl-2-picrylhydrazyl free radical scavenging and lipid peroxidation inhibition assays. The α-tocopherol was used as a reference compound. The physical stability (using rheology, polarization microscopy, pH and conductivity measurements) of an Alkyl glucoside-based emulsion was evaluated with and without the active (LA); colloidal structure was assessed using polarization and transmission electron microscopy, rheology, thermal and texture analysis. Additionally, the safety profile and moisturizing potential were investigated using the methods of skin bioengineering. Good physical stability and applicative characteristics were obtained although LA strongly influenced the colloidal structure of the vehicle. LA per se and in APG-based emulsion showed satisfying antioxidant activity that promotes it as mild multifunctional cosmeceutical efficient in the treatment and prevention of the photoaged skin. Employed assays were shown as suitable for the antioxidant activity evaluation of LA in APG-based emulsions, but not for α-tocopherol in the same vehicle.

Formulation, Rheology, and Hypolepidemic Activity of Vegetable Oil-Based Eggless and Low-Fat Food Emulsions

Common edible oils such as almond, safflower, soybean, and mustard oil were formulated in the form of eggless and low-fat oil-in-water emulsions using a blend of nonionic emulsifier Glycerol monostearate and amphoteric emulsifier soy lecithin. The emulsion parameters such as vegetable oil, emulsifier, additive content and hydrophilic-lipophilic balance number of emulsifier were optimized. The storage stability of formulated emulsions was monitored under accelerated storage stability conditions for six months. Rheological characterization of stable emulsion revealed pseudoplastic flow behavior. In vivo hypolepidemic activity of formulated emulsions in rats showed considerable reduction in total cholesterol and triglyceride level after 14 days as compared with the marketed product. The almond oil emulsion is found superior than safflower oil emulsion.

Prediction and Experimental Measurements of Water-in-Oil Emulsion Viscosities During Alkaline/Surfactant Injections

Summary Oil production is generally a complicated multiphase flow inside pipelines, with possible water-in-oil (W/O) emulsions present with other usual phases such as free water and free oil. The W/O emulsions formed can present significant hurdles in production facilities for pumping fluids and during pipeline transport. It is well known that high shear rates provided by pumps, chokes, or valves result in stable emulsion behavior for a field in primary production. Several field tests are under way to test the potential of surfactant flooding as a tertiary-recovery mechanism. The effect of addition of surfactants on the emulsion rheology of production fluids, as in alkaline/surfactant/polymer (ASP) flooding, is not very well understood. This understanding of W/O-emulsion rheology in ASP-injection oil recovery is essential for design of pumps and pipelines as well as for handling flow-assurance issues. In this paper, we report results from experiments as well as modeling of W/O-emulsion rheology that can form during ASP injections. We focus here only on the alkaline/surfactant (AS) part of these injections in order to clearly understand the impact of surfactants, removing the uncertainities that come with large rheology changes with polymer addition. The effect of surfactants on the rheology of W/O emulsions was studied by making two different types of emulsions: (1) native-brine W/O emulsions without surfactants to provide a baseline and (2) brine W/O emulsions with surfactants used in ASP injections. This way, the impact of ASP injections on emulsion rheology can easily be quantified. A new correlation is developed, based on in-house historical experimental data, to describe rheology of emulsions without surfactants. This correlation should assist in managing the uncertainties that come from extrapolating emulsion rheology measured in the laboratory to actual field conditions. Further, to understand the effect of ASP injections, new experimental measurements were made by adding surfactants to brine solutions. The addition of surfactants resulted in different rheology as compared with emulsions formed by brine solutions. These differences have been attributed to the W/O interfacial tension (IFT), and IFT was added to modify the original correlation. To our knowledge, this is the first study that explicitly relates emulsion rheology with IFT.

Modulation of emulsion rheology through electrostatic heteroaggregation of oppositely charged lipid droplets: Influence of particle size and emulsifier content

The influence of electrostatically-induced heteroaggregation of oppositely charged lipid droplets on the rheology and stability of emulsions has been studied. 20wt.% oil-in-water emulsions (pH 6) containing oppositely charged droplets were fabricated by mixing cationic lactoferrin-coated lipid droplets with anionic β-lactoglobulin-coated lipid droplets. Emulsions containing mixtures of droplets with different charges (positive or negative) and sizes (large or small) were prepared, and then their overall particle characteristics (ζ-potential and size) and rheology were measured. Emulsions formed by mixing positive droplets and negative droplets that were both relatively small (d43≈0.3μm) exhibited extensive flocculation and had paste-like properties at intermediate positive-to-negative particle ratios. On the other hand, emulsions formed by mixing positive droplets and negative droplets that were both relatively large (d43≈3μm) exhibited little aggregation and had relatively low viscosities at all particle ratios. Emulsions with small negative droplets and large positive droplets (or vice versa), exhibited some aggregation and viscosity enhancement at intermediate particle ratios. The presence of relatively high levels of protein in the aqueous phase of mixed emulsions reduced the level of droplet aggregation and viscosity enhancement observed, which was attributed to the ability of protein molecules to bind to droplet surfaces and neutralize their charges. Electrostatically-induced heteroaggregation of lipid droplets may be a useful means of controlling the physicochemical properties of emulsion-based products in the food, personal care, pharmaceutical and cosmetic industries.

Direct numerical simulation of surfactant-stabilized emulsions

A 3D lattice Boltzmann model for two-phase flow with amphiphilic surfactant was used to investigate the evolution of emulsion morphology and shear stress in starting shear flow. The interfacial contributions were analyzed for low and high volume fractions and varying surfactant activity. A transient viscoelastic contribution to the emulsion rheology under constant strain rate conditions was attributed to the interfacial stress. For droplet volume fractions below 0.3 and an average capillary number of about 0.25, highly elliptical droplets formed. Consistent with affine deformation models, gradual elongation of the droplets increased the shear stress at early times and reduced it at later times. Lower interfacial tension with increased surfactant activity counterbalanced the effect of increased interfacial area, and the net shear stress did not change significantly. For higher volume fractions, co-continuous phases with a complex topology were formed. The surfactant decreased the interfacial shear stress due mainly to advection of surfactant to higher curvature areas. Our results are in qualitative agreement with experimental data for polymer blends in terms of transient interfacial stresses and limited enhancement of the emulsion viscosity at larger volume fractions where the phases are co-continuous.

Rheology and Microstructure of Lecithin-Stabilized Tuna Oil Emulsions Containing Chitosan of Varying Concentration and Molecular Size

The purpose of these experiments was to determine the influence of chitosan concentration (0–0.25 wt.%) and molecular weight (120, 250 and 342.5 kDa) on the rheological properties and microstructure of lecithin-stabilized tuna oil emulsions. The apparent viscosity of the emulsions significantly increased with increasing chitosan concentration and molecular weight (P ≤ 0.05). However, the studied chitosan chain lengths did not play a major role in determining the flow characteristics of the emulsions. The emulsions containing 0.1–0.25 wt.% chitosan were stable to droplet aggregation. All of these emulsions showed Newtonian flow with a flow behavior index of approximately 1. In the contrary, the 0.05 wt.% chitosan emulsions showed highly unstable droplet aggregation and a shear thinning behavior. The emulsion microstructure visualized using a confocal laser scanning microscope was consistent with the rheological data. These results have important implications for the utilization of tuna oil emulsions stabilized by lecithin-chitosan membranes in emulsion based food products.

Rheology and Structure of Emulsions and Suspensions

This article contains the results of experimental investigation of the rheological characteristics and structures of emulsions and suspensions. The emulsions had the oil volume fraction in the range from 0.1 to 0.4. The suspensions with nanoparticles are represented by suspensions of silica with concentrations from 1 to 4%. Paprika and coffee suspensions with concentrations of 5, 10, and 20% were studied. The material was subjected to rheological measurements using a concentric cylinder viscometer in the shear rate range of 16.2 to 1326s−1. A lot of food products are either in the form of emulsions or suspensions whose rheological and interfacial properties are important to achieve stability of the products. The rheology and structure analysis is very important from the point of view of flow, friction factors and Reynolds number for non-Newtonian fluids and food production processes. To characterize emulsions and suspensions, first the particle size distributions were made. The experiments presented have shown that the rheological characteristics of composite systems (emulsions and suspensions) depend on concentration and properties of dispersed phase. Concentration of dispersed phase has an effect on the character of the fluid. The fluid can have Newtonian character at low concentrations of dispersed phase. Above certain concentrations the nature of non-Newtonian fluid will appear. Emulsions have a polydisperse character. Emulsions with ϕ up to 0.4 show approximately linear increase of emulsion viscosity on the oil concentration. Silica represents suspension with aggregates, agglomerates or network formed. The increase in shear rate causes gradual destruction of the structure. The rheological behaviors confirm these processes. The paprika and coffee suspensions have non-Newtonian rheological properties. The suspensions have more and more non-Newtonian characteristics increasing particles concentration. The solid particles do not form structures. The correlation equation for rheological properties of systems studied has been shown. The results may be used for example to verify numerical models or comparisons with respect to similar fluids.

Study of aggregational characteristics of emulsions on their rheological properties using the lattice Boltzmann approach

Predicting the rheological properties of emulsions is one of the most challenging and complicated problems in material and fluid sciences. Substantial complications in prediction of rheology arise due to the deformability and aggregation of emulsions. Thus a better understanding of deformation and aggregation of emulsions can lead to a better understanding of the shear thinning region of emulsions. Though numerous experimental and theoretical studies were performed to obtain rheological correlations of emulsions, their inability to visualize and understand the droplet deformation in the presence of large volume fractions has stagnated our understanding of the shear thinning behavior of emulsions. With the aid of a numerical tool, which can help in visualizing the droplet deformation and correlate it to rheological behavior of emulsions, we have made an attempt to understand the physics behind the shear thinning behavior and also predict its rheological characteristics for emulsions at different volume fractions. In this article, we try to obtain a theoretical understanding of the influence of deformation and de-aggregation of droplets on the emulsion rheology. Simulations performed in this article using a multi-component lattice Boltzmann model are used to quantify (a) relative viscosity of emulsions with change in shear rate, (b) relative viscosity of emulsions with change in time, (c) effect of deformation of droplets on the shear thinning region in emulsions, and (d) relative viscosity of emulsions with change in volume fraction.

Isolation, characterization and emulsion stabilizing properties of polysaccharides form orchid roots (salep)

Polysaccharide extracts were isolated from ground salep (dried orchid root). These were studied in terms of their composition and their capacity to affect the rheology and stability of emulsions. Successive extractions yielded three separate extracts, namely HBSS (hot buffer soluble solids, extracted at 70 °C, pH = 5.2), CHSS (chelating agent soluble solids, extracted at 70 °C, pH = 5.2), and DASS (diluted alkali soluble solids, extracted at 0 °C). HBSS comprised of negatively charged macromolecular populations sizing approximately between 600 kDa–700 kDa (d ∼ 500 nm), one at 50 kDa (d ∼ 70 nm), and a third one at 12 kDa (d ∼ 20 nm). Upon addition into Tween 20-stabilized emulsions, HBSS caused flocculation and enhanced creaming at low concentrations (0.1%), while at higher concentrations (≥0.7%) it drastically reduced creaming due to the increase of the aqueous phase viscosity.CHSS extracts contained a negatively charged polysaccharide population of approximately 50 kDa (d ∼ 140 nm). DASS extracts contained only small molecules. Addition of CHSS or DASS extracts into Tween 20-stabilized emulsions did not affect the viscosity or the creaming stability of the emulsions. Flocculation was induced at 2% CHSS. This can be predicted by a simple depletion model. The above suggest that salep hydrocolloids are highly efficient thickeners that can be extracted in a one-step process.

Rheology of attractive emulsions

We show how attractive interactions dramatically influence emulsion rheology. Unlike the repulsive case, attractive emulsions below random close packing, φ(RCP), can form soft gel-like elastic solids. However, above φ(RCP), attractive and repulsive emulsions have similar elasticities. Such compressed attractive emulsions undergo an additional shear-driven relaxation process during yielding. Our results suggest that attractive emulsions begin to yield at weak points through the breakage of bonds, and, above φ(RCP), also undergo droplet configurational rearrangements.

Rheology of Acacia-Stabelised Emulsions

Abstract The flow behaviour of emulsions of benzene and two paraffin oils in acacia solutions has been examined. The concentration of acacia had little effect on the relative viscosity, and the viscosity of the oil none. Emulsion viscosity increased with the volume fraction of oil which also led to an increased deviation from Newtonian flow. Evidence of thixotropy was not found in these emulsions. The chemical nature of the oil has a great influence on the viscosity and the differences are explained in terms of the characteristics of the interfacial film.

Proceedings: The influence of alcohol chain length on the structure and rheology of emulsions stabilized by cetomacrogol/long chain alcohols.

Proceedings: The influence of alcohol chain length on the structure and rheology of emulsions stabilized by cetomacrogol/long chain alcohols.