Rheology Of Emulsions Research Articles

A new mesh relaxation approach and automatic time‐step control method for boundary integral simulations of a viscous drop

SummaryWe present a numerical methodology for the simulation of a viscous drop under simple shear flows by using the boundary integral method. The present work treats only a single drop in an unbounded fluid‐flow, but the results can be directly applied to studies on the rheology of dilute emulsions, in which the hydrodynamic interactions between two or more drops can be neglected. Singular and non‐singular integral representations of the velocity field are considered. Several aspects of the method are presented, including a new mesh relaxation approach and an automatic time‐step control method. The relaxation strategy is used in order to contain the distortion of the mesh and is performed by using relaxation iterations in a virtual temporal march between each physical time step of the simulation and monitoring the standard deviation of the areas of the elements. The automatic time‐step control method uses a global quantity related to the drop deformation in order to automatically set the temporal integration time step. It is carried out in a way to keep the local integration error less than a given tolerance. This strategy reduces the computational cost of the simulation by dramatically reducing the number of time steps in the temporal integration process. Copyright © 2016 John Wiley & Sons, Ltd.

Optimization of nanoemulsions processed by high-pressure homogenization to protect a bioactive extract of jackfruit (Artocarpus heterophyllus Lam)

The present work investigates the development of an eco-friendly nanoemulsion to maintain the bioactivity of a rich in carotenoids extract from jackfruit (Artocarpus heterophyllus Lam) pulp. Firstly, the influence of the sucrose monostearate (SMS) content (0.5–2%, w/w), miglyol content (5–20%, w/w) and homogenization pressure (400–800 bar) on the droplet size distribution, rheology and stability of emulsions processed by high-pressure homogenization was studied. Except two formulations containing the highest SMS content and processed at the lowest pressure, stable fluid submicron emulsions were obtained. Then, a jackfruit pulp extract was incorporated in the oily phase of the selected emulsion (5% miglyol plus 0.5% SMS processed twice in a high-pressure homogenizer at 800 bar). The antioxidant activity of the jackfruit extract loaded in the selected emulsion stored at 4 °C has exhibited a longer stability compared to the same extract only dissolved in miglyol and stored in same conditions.

Steady shear rheology of a viscous emulsion in the presence of finite inertia at moderate volume fractions: sign reversal of normal stress differences

The shear rheology of an emulsion of viscous drops in the presence of finite inertia is investigated using direct numerical simulation. In the absence of inertia, emulsions display a non-Newtonian rheology with positive first and negative second normal stress differences. However, recently it was discovered that a small amount of drop-level inertia alters their signs – the first normal stress difference becomes negative and the second one becomes positive, each in a small range of capillary numbers (Li & Sarkar,J. Rheol., vol. 49, 2005, pp. 1377–1394). Sign reversal was shown numerically and analytically, but only in the limit of a dilute emulsion where drop–drop interactions were neglected. Here, we compute the rheology of a density- and viscosity-matched emulsion, accounting for the interactions in the volume fraction range of 5 %–27 % and Reynolds number range of 0.1–10. The computed rheological properties (effective shear viscosity and first and second normal stress differences) in the Stokes limit match well with previous theoretical (Choi–Schowalter in the dilute limit) and simulated results (for concentrated systems) using the boundary element method. The two distinct components of the rheology arising from the interfacial stresses at the drop surface and the perturbative Reynolds stresses are investigated as functions of the drop Reynolds number, capillary number and volume fraction. The sign change is caused by the increasing drop inclination in the presence of inertia, which in turn directly affects the interfacial stresses. Increase of the volume fraction or capillary number increases the critical Reynolds number for sign reversals due to enhanced alignment of the drops with the flow directions. The effect of increasing the volume fraction on the rheology is explained by relating it to interactions and specifically to the contact pair-distribution function computed from the simulation. The excess stresses are seen to show an approximately linear behaviour with the Reynolds number in the range of 0.1–5, while with the capillary number and volume fraction, the variation is weakly quadratic.

Influence of Nanoparticles and Drop Size Distributions on the Rheology of w/o Pickering Emulsions

AbstractThe rheological behavior of particle/oil suspensions and w/o Pickering emulsions consisting of water, 1‐dodecene and different fumed silica nanoparticles was investigated. The particles varied in hydrophobicity and specific surface area. The influence of particle concentration and water content on rheology was determined and the emulsion drop size distributions were examined. Emulsions with different drop sizes were created by either varying the particle concentration or the water content. It was found that the particles in the continuous oil phase and not the drop size distribution seem to be the major influencing factor on the Pickering emulsion rheology.

The role and interaction of superplasticizer and emulsifier in fresh cement asphalt emulsion paste through rheology study

The workability and mechanical properties of cement asphalt emulsion (CA) mortar are unstable due to the complex interaction between cement and asphalt emulsion. To reveal the interaction between cement and asphalt emulsion, the effect of emulsifier and superplasticizer on the rheology of cement paste and asphalt emulsion is investigated, respectively, and the effect of the interaction between emulsifier and superplasticizer on the rheology of cement paste is studied in this paper as well. Results show that the apparent viscosity and yield stress of asphalt emulsion increase with superplasticizer and emulsifier dosage. Emulsifier can change the yield stress and apparent viscosity of cement paste, and its effect on cement paste differs greatly with the type and dosage of emulsifier. Some emulsifiers can increase the yield stress of cement paste, but some emulsifiers can decrease the yield stress of cement paste. Emulsifier has interaction with superplasticizer, thus affecting the reducing water effect of superplasticizer on cement paste. There is a competition relationship between emulsifier and superplasticizer when they are adsorbed by cement particles. The mixing method, in which superplasticizer is mixed with cement before emulsifier added, is beneficial to obtain a lower apparent viscosity of cement paste for all tested emulsifiers.

Bulk and interfacial rheology of emulsions stabilized with clay particles

This contribution aims to investigate the stabilizing effect of clay particles on oil-in-water emulsions using bulk and interfacial rheological measurements. Depending on the surface properties of clay particles, the emulsion showed different rheological responses as a result of different stabilization behavior. Hydrophilic clays (natural montmorillonite (NMt)) stabilized the emulsion via an interfacial layer with distinguished interfacial modulus (G*interface), while hydrophobic clays (organically modified montmorillonite (OMt)) stabilized the emulsion by increasing the bulk modulus of the oil phase (G*oil). In composite systems, when NMt is present together with cationic surfactant or OMt, complex formation at the oil-water interface significantly influenced the rheological response and emulsion stability. The high interfacial modulus (G*interface) of the composite interface stabilized the flocculated droplets more than the repulsive interaction between droplets. As a consequence, the bulk modulus of the emulsion (G*emulsion) also increases. Finally it could be shown that with increasing interfacial area (oil-to-water ratio), microscopic and macroscopic stabilization of emulsions could be improved. Rheological study provided structural information of the complex interface and defined the role of clay particles for the stabilization.

Dual modification of starch nanocrystals via crosslinking and esterification for enhancing their hydrophobicity

The aim of this study was to enhance the hydrophobicity of starch nanocrystals (SNCs) and improve their dispersibility in non-polar solvents through dual modifications. The dual modifications were carried out by crosslinking first and then followed esterification. The results of characterizations showed that the dual modifications resulted in a higher degree of substitution of SNCs than single esterification modification. The SNCs with the dual modifications possessed lower polarity and showed stronger hydrophobicity than the SNCs with single crosslinking or esterification modification and therefore could be dispersed in non-polar solvents such as chloroform, dichloromethane and toluene. In addition, the crosslinking protected the crystalline structure of SNCs being disrupted in the followed esterifications. The modified SNCs can be used as reinforcements for nanocomposites with hydrophobic polymer matrices or emulsion stabilizers and rheology modifiers.

Experimental study on high-pressure rheology of water/crude oil emulsion in the presence of methane

ABSTRACTThe crude oil is in most cases accompanied with water and natural gas. For this reason, it is important to understand the rheology of the oil emulsion. There are already many works relating to rheology of the oil/water emulsion. However, studies on high-pressure rheology of water/crude oil emulsion in the presence of CH4 are rare. In this work, light crude oil with characteristics of high wax content, which is typical in Northwest China, was studied. The rheology of water/crude oil emulsion in the presence of CH4 under various conditions were fully studied. The results show that the crude oil emulsion showed obvious characteristics of non-Newtonian fluid at a lower temperature. Before water fraction reached a certain limit, the viscosity increases with the increase of water fraction, when water fraction reaches and exceeds the limit the emulsion viscosity drops with the increase of water fraction. The shear stress–shear rate curves become similar as the increase of temperature, indicating the decreasing effect of temperature on the relation between shear stress and shear rate. When the pressure reaches 8 MPa, the shear stress measured with CH4 in the system surpasses that measured without CH4. At higher pressure, CH4 shows obvious influence on the rheology.

Effect of emulsifier type on physicochemical properties of water‐in‐oil emulsions for confectionery applications

SummaryIn a first step of designing tailored confectionery masses using water‐in‐oil emulsions, a parameter screening on emulsion rheology and stability was carried out. The experimental set‐up included cocoa butter as continuous phase and the variation of the disperse phase (water, or 50% sucrose in water), two volume fraction levels and the type of emulsifier (lecithin, polyglycerol polyricinoleate (PGPR), ammonium phosphatide (YN) and blends of lecithin or YN with PGPR). Emulsions were characterised by microscopy, laser diffraction, analytical centrifugation and shear rheology. Results show multimodal droplet size distributions in lecithin‐ or YN‐stabilised emulsions, and droplets which tend to form aggregates and an internal network responsible for shear thinning. PGPR emulsions are characterised by monomodal droplet size distributions and smaller droplets without networking tendency. They exhibit Newtonian flow behaviour and a much higher stability against phase separation. In emulsifier blends, PGPR is mainly responsible for the modulation of physical properties of the emulsions.

Influence of Cement on Rheology and Stability of Rosin Emulsified Anionic Bitumen Emulsion

AbstractOrdinary portland cement (OPC) has been extensively used in cold recycling asphalt and cold-mix asphalt as an additive in order to improve the early age performances of these mixtures. The main purpose of its application is that cement hydration benefits the strength development by consuming water and by accelerating the bitumen emulsion breaking. The aim of this study is to investigate the influence of cement on the rheology and stability of rosin-emulsified anionic bitumen emulsions. With this purpose, an anionic bitumen emulsion blended with various amounts of cement and limestone filler was studied by means of a Brookfield viscometer. Optical microscopy was used to investigate the breaking process of the bitumen emulsion and the morphology of bitumen droplets in the presence of cement and filler. In addition, the stability of anionic bitumen emulsions was studied in dependence of the pH and the calcium ion concentration. The results indicate that, unlike limestone filler, which has no signific...

Effect of rheology of dense emulsions on the flow structure in agitated systems

In manufacturing and applying emulsions it is often necessary to predict or control their flow and adjust their viscosity. A new method is presented for including the effect of the droplet size distribution on the rheological behaviour of dense oil-in-water emulsions of noncolloidal droplets. The method is based on extension of the advanced model for the relative viscosity of the concentrated monodisperse emulsion to account for polydispersity effects. The model includes effects of volume fraction of the dispersed phase, droplet size distribution, interfacial tension and shear rate on the relative emulsion viscosity. The model has universal character and can be combined with the population balance equation and CFD. Examples of modelling are presented for laminar and turbulent flows of dense emulsions. In the case of laminar flow the Couette flow and the Taylor–Couette flow are considered. In the case of turbulent flow it is shown how dispersion of droplets in the high-shear rotor-stator mixer affects the flow pattern and rheology of the emulsion product.

Development and rheological properties of ecological emulsions formulated with a biosolvent and two microbial polysaccharides

The influence of gum concentration and rhamsan/welan gum ratio on rheological properties, droplet size distribution and physical stability of eco-friendly O/W emulsions stabilized by an ecological surfactant were studied in the present work. The emulsions were prepared with 30wt% α-pinene, a terpenic solvent and an ecological alternative for current volatile organic compounds. Rheological properties of emulsions showed an important dependence on the two studied variables. Flow curves were fitted to the Cross model and no synergistic effect between rhamsan and welan gums was demonstrated. Emulsions with submicron mean diameters were obtained regardless of the gum concentration or the rhamsan/welan ratio used. Multiple light scattering illustrated that creaming was practically eliminated by the incorporation of polysaccharides. The use of rhamsan and welan gums as stabilizers lead to apparent enhancements in emulsion rheology and physical stability.

Emulsion rheology for steady and oscillatory shear flows at moderate and high viscosity ratio

A numerical simulation scheme based on a three-dimensional boundary integral method is used for the purpose of estimating the macroscopic flow from the microscale drop deformation for emulsions of high viscosity ratio under steady, oscillatory shear, and extensional flows. The effects of drop deformation and shear rate are examined for moderate and high viscosity ratio. The accuracy and convergence of the numerical simulations is illustrated by comparing drop deformation and rheology with experimental observations and an asymptotic theory based on a second-order small deformation theory also developed in this work. We also examine an emulsion undergoing a pure extensional flow and an extensional viscosity of the emulsion is computed by the theory and the numerical simulations. In addition, we also explore regimes of linear and nonlinear viscoelasticity when the emulsion is subjected to oscillatory shear for different viscosity ratio. Emulsion Fourier modes are examined for two different viscosity ratio. For a more concentrate emulsion with an unit viscosity ratio, a static shear elastic modulus is computed as a function of drop volume fraction and compared with experimental data. The numerical simulation results are validated against theory and experimental observation of drops in shear and extensional flows. A very good agreement is observed for moderate and high viscosity ratio. The regime of emulsions with relatively high viscosity ratios has not been much explored in the current theoretical and experimental literature. The boundary integral numerical simulations developed in this work has the ability to predict what we expect on the behavior of emulsion with moderate and high viscosity ratio.

Influences of Ulva fasciata polysaccharide on the rheology and stabilization of cinnamaldehyde emulsions

Emulsifying properties of water soluble polysaccharides from Ulva fasciata (UFP) were evaluated in cinnamaldehyde/water emulsions in terms of droplet size distribution, rheological properties, visual phase separation, and zeta-potential. The cinnamaldehyde/water (10%, wt/wt) emulsions were formulated and stabilized by different concentrations of UFP (0.1–4%, wt/wt). The obtained emulsions showed monomodal droplet size distributions with average droplet size (D[3,2]) below 1.0μm, when 3% (wt/wt) UFP was added as the emulsifying agent under a homogenization pressure of 75MPa. The rheological properties and zeta-potential of the emulsions appeared to be dependent on the UFP concentration. Furthermore, the UFP exhibited better emulsifying and stabilizing properties in the investigated system when compared to other commercial polysaccharides of gum Arabic and gum Ghatti. The results also suggested that the emulsifying and stabilizing mechanism of the UFP may not only be ascribed to its surface-active protein moiety, but also to the hydrophobicity of the polysaccharide itself. These findings provided a theoretical basis for potential utilization of UFP as a novel hydrocolloid emulsifying agent.

Investigation of synergy between nanoparticle and surfactant in stabilizing oil-in-water emulsions for improved heavy oil recovery

This study presents an experimental study, including phase behavior tests, rheology studies, core flooding and microscopic visualization tests for investigating the synergistic effect of nanoparticles and surfactants in stabilizing oil-in-water (O/W) emulsions for improved heavy oil recovery. The emulsion stability and rheology studies show that the addition of nanoparticles can not only improve the stability of the emulsion, but also greatly increase the bulk viscosity of emulsion. The core flooding conducted with the nanoparticle-surfactant stabilized emulsion show a marked improvement in oil recovery over the surfactant-stabilized emulsions. The tertiary oil recovery can reach over 40% of the initial oil in place (IOIP) for crude oil with the viscosity of 350 mPa s at 50 °C. The micromodel tests indicate that the nanoparticles can thicken the emulsion to the desirable mobility, which can damp the viscous fingering phenomena to dramatically improve sweep efficiency. In addition, the heavy oil can be emulsified into the water phase to form oil-in-water emulsions with the aid of the surfactant. These results demonstrate that the nanoparticle-surfactant stabilized emulsion has a great potential for enhanced oil recovery in waterflooded heavy oil reservoirs.

Extensional and shear flows, and general rheology of concentrated emulsions of deformable drops

The rheology of highly concentrated monodisperse emulsions is studied by rigorous multidrop numerical simulations for three types of steady macroscopic flow, (i) simple shear ($\dot{{\it\gamma}}x_{2}$, 0 0), (ii) planar extension (PE) ($\dot{{\it\Gamma}}x_{1},-\dot{{\it\Gamma}}x_{2},0$) and (iii) mixed ($\dot{{\it\gamma}}x_{2}$, $\dot{{\it\gamma}}{\it\chi}x_{1}$, 0), where $\dot{{\it\gamma}}$ and $\dot{{\it\Gamma}}$ are the deformation rates, and ${\it\chi}\in (-1,1)$ is the flow parameter, in order to construct and validate a general constitutive model for emulsion flows with arbitrary kinematics. The algorithm is a development of the multipole-accelerated boundary-integral (BI) code of Zinchenko & Davis (J. Fluid Mech., vol. 455, 2002, pp. 21–62). It additionally incorporates periodic boundary conditions for (ii) and (iii) (based on the reproducible lattice dynamics of Kraynik–Reinelt for PE), control of surface overlapping, much more robust controllable surface triangulations for long-time simulations, and more efficient acceleration. The emulsion steady-state viscometric functions (shear viscosity and normal stress differences) for (i) and extensiometric functions (extensional viscosity and stress cross-difference) for (ii) are studied in the range of drop volume fractions $c=0.45{-}0.55$, drop-to-medium viscosity ratios ${\it\lambda}=0.25{-}10$ and various capillary numbers $\mathit{Ca}$, with 100–400 drops in a periodic cell and 2000–4000 boundary elements per drop. High surface resolution is important for all three flows at small $\mathit{Ca}$. Large system size and strains $\dot{{\it\gamma}}t$ of up to several thousand are imperative in some shear-flow simulations to identify the onset of phase transition to a partially ordered state, and evaluate (although still not precisely) the viscometric functions in this state. Below the phase transition point, the shear viscosity versus $\mathit{Ca}$ shows a kinked behaviour, with the local minimum most pronounced at ${\it\lambda}=1$ and $c=0.55$. The ${\it\lambda}=0.25$ emulsions flow in a partially ordered manner in a wide range of $\mathit{Ca}$ even when $c=0.45$. Increase of ${\it\lambda}$ to 3–10 shifts the onset of ordering to much smaller $\mathit{Ca}$, often outside the simulation range. In contrast to simple shear, phase transition is never observed in PE or mixed flow. A generalized five-parameter Oldroyd model with variable coefficients is fitted to our extensiometric and viscometric functions at arbitrary flow intensities (but outside the phase transition range). The model predictions compare very well with precise simulation results for strong mixed flows, ${\it\chi}=0.25$. Time-dependent PE flow is also considered. Ways to overcome the phase transition and drop breakup limitations on constitutive modelling are discussed.

Influence of the ratio of amphiphilic copolymers used as emulsifiers on the microstructure, physical stability and rheology of α-pinene emulsions stabilized with gellan gum

α-Pinene is a terpenic solvent whose use in the formulation of emulsions entails a double benefit from the environmental point of view since it is a green solvent, easily biodegradable, which also has certain antimicrobial properties.In this work a combination of Atlas™ G-5000 and Atlox™ 4913 amphiphilic copolymers was used to obtain O/W emulsions formulated with α-pinene and gellan gum. These emulsions may find applications related to the design of complex biotechnological systems with different uses.In order to investigate the microstructure and the physical stability of these emulsions, a combination of different techniques such as rheology, microscopy, laser diffraction and multiple light scattering turn out to be a useful methodology.The results demonstrated the need to include a minimum amount of Atlas™ G-5000 copolymer in the formulation of these emulsions to improve their stability. These results were supported by the information revealed by optical micrographs, according to which Atlas™ G-5000 is directed to the continuous medium to structure water (this surfactant is particularly effective at forming hydrogen bonds with water). On the other hand Atlox™ 4913 is preferentially adsorbed at the α-pinene–water interface, such that a high Atlox™ 4913/Atlas™ G-5000 mass ratio slows down the kinetics of coalescence as shown by multiple light scattering. However, a very low relative concentration of Atlas™ G-5000 causes creaming to become the dominant destabilization mechanism. Increasing the Atlas™ G-5000/Atlox™ 4913 mass ratio yields emulsions with enhanced viscosity and viscoelasticity.

Cross-linking proteins by laccase: Effects on the droplet size and rheology of emulsions stabilized by sodium caseinate

The aim of this work was to evaluate the influence of laccase and ferulic acid on the characteristics of oil-in-water emulsions stabilized by sodium caseinate at different pH (3, 5 and 7). Emulsions were prepared by high pressure homogenization of soybean oil with sodium caseinate solution containing varied concentrations of laccase (0, 1 and 5mg/mL) and ferulic acid (5 and 10mM). Laccase treatment and pH exerted a strong influence on the properties with a consequent effect on stability, structure and rheology of emulsions stabilized by Na-caseinate. At pH7, O/W emulsions were kinetically stable due to the negative protein charge which enabled electrostatic repulsion between oil droplets resulting in an emulsion with small droplet size, low viscosity, pseudoplasticity and viscoelastic properties. The laccase treatment led to emulsions showing shear-thinning behavior as a result of a more structured system. O/W emulsions at pH5 and 3 showed phase separation due to the proximity to protein pI, but the laccase treatment improved their stability of emulsions especially at pH3. At pH3, the addition of ferulic acid and laccase produced emulsions with larger droplet size but with narrower droplet size distribution, increased viscosity, pseudoplasticity and viscoelastic properties (gel-like behavior). Comparing laccase treatments, the combined addition of laccase and ferulic acid generally produced emulsions with lower stability (pH5), larger droplet size (pH3, 5 and 7) and higher pseudoplasticity (pH5 and 7) than emulsion with only ferulic acid. The results suggested that the cross-linking of proteins by laccase and ferulic acid improved protein emulsifying properties by changing functional mechanisms of the protein on emulsion structure and rheology, showing that sodium caseinate can be successfully used in acid products when treated with laccase.

Chia seed oil-in-water emulsions as potential delivery systems of ω-3 fatty acids

Chia oil can be incorporated into oil-in-water (O/W) emulsions as ω-3 fatty acid delivery systems in food matrices. Chia O/W emulsions varying in sodium caseinate (NaCas) concentration (2, 5 and 10% (wt/wt)), with and without 10% (wt/wt) lactose and using different homogenization pressures (400, 600bar) were prepared, stored at 4±1°C and analyzed as a function of particle size, ζ-potential, rheological properties, backscattering profiles, peroxide and p-anisidine values. Droplet characteristics, rheology and stability of emulsions are influenced with different extent by the factors analyzed. All systems recorded negatively charged droplets and unimodal particle size distribution. Emulsions with 2 and 5% (wt/wt) NaCas presented a Newtonian fluid behavior. The former showed moderate stability to creaming, while the latter presented destabilization by flocculation and creaming few hours after preparation. Emulsions with 10% (wt/wt) NaCas showed a pseudoplastic fluid behavior and high stability by the rearrangement of the aggregates into a firm gel network. Chia O/W emulsions exhibited a good oxidative stability.

Modeling the steady-shear rheological behavior of dilute to highly concentrated oil-in-water (o/w) emulsions: Effect of temperature, oil volume fraction and anionic surfactant concentration

Oil-in-water (o/w) emulsions having different internal phase concentrations have been encountered in the petroleum industry during production, transportation and storage operations. The present study deals with the rheological behavior of o/w emulsions of varying internal phase (oil) concentrations (10–80%) at different temperatures (25–50 °C). A controlled stress rotational viscometer was used with shear rates ranging from 1 to 100 s−1. The emulsions were prepared with an anionic surfactant sodium dodecyl benzene sulfonate (SDBS) and the concentration of the surfactant was varied from 0.5 to 2 w/v %. The emulsions exhibited typical shear thinning behavior and described well by the power law relationship between shear stress and shear rate. Different viscosity models were tested and fitted with the experimental rheological data using rigorous-linear regression analysis. The emulsion viscosity and pseudoplasticity were found to increase with an increase in oil concentration and decrease with an increase in temperature. Droplet size distribution and surface tension (SFT) measurements showed that both droplet size and SFT of emulsions decreased with an increase in the oil concentration, which significantly influenced the emulsion rheology. The effect of oil concentration on the apparent viscosity of emulsions was correlated by an exponential and a polynomial model. Further, a correlation was proposed for the combined effect of volume fraction and temperature on viscosity of emulsions. At higher concentrations of SDBS, the emulsion showed yield stress to flow. The Herschel–Bulkley model described the rheological data significantly well.