Volume Fraction Of Dispersed Phase Research Articles

Extent and mechanism of coalescence in rotor-stator mixer food-emulsion emulsification

Food-emulsions often have high volume fractions of dispersed phase and are thus expected to show coalescence during emulsification, however, food-emulsion coalescence is difficult to measure in homogenizer equipment. This study experimentally estimates the rates of fragmentation and coalescence in a high viscosity and high volume fraction model emulsion subjected to pilot-scale rotor-stator mixing in order to quantify the relative effect of coalescence and discuss the mechanism of coalescence during batch processing of high-fat emulsion foods. Rate constants of both processes are estimated using a previously suggested method relying on parameter fitting from the dynamic evolution of the total number of emulsion drops (Hounslow and Ni, 2004). The results show substantial coalescence taking place. Scaling of rates with respect to rotor tip speed suggests coalescence and fragmentation controlled by a turbulent viscous mechanism.

Gelation of oil-in-water emulsions stabilized by whey protein

The effects of heat treatment and high-pressure homogenization on whey protein (WP) emulsion properties were evaluated. Only emulsion containing non-heated WP was stable, presenting low viscosity, small droplets and higher adsorbed protein content by increasing homogenization pressure. In addition, the influence of high-pressure homogenization and pH on cold-set gel formation by acidification of emulsion (emulsion gel) or emulsion dispersed in heat-treated WP solution (emulsion-filled gel) was studied. Only emulsion-filled gels were self-supported. Stronger gels were observed at pH near WP isoelectric point due to lower acidification rate and electrostatic repulsion that promoted more intense protein aggregation. Varying emulsion homogenization pressure resulted in different gel network strength caused by changing dispersed phase volume fraction and adsorbed protein content. Therefore, depending on process conditions cold-set gel of emulsion can be produced and it shows a great potential to be used in food formulations as texturizing agent and/or as a carrier for heat-labile ingredients.

Development of microfluidization methods for efficient production of concentrated nanoemulsions: Comparison of single- and dual-channel microfluidizers

Nanoemulsions are being increasingly utilized within the pharmaceutical, food, personal care, and chemical industries because of their unique physicochemical properties and functional performances: high optical clarity; prolonged stability; enhanced bioavailability; and novel rheology. For commercial applications, it is important to be able to produce nanoemulsions containing small droplets using efficient homogenization processes. In this study, we compared two microfluidization methods for fabricating nanoemulsions: (i) single-channel microfluidization and (ii) dual-channel microfluidization. The influence of emulsifier concentration, homogenization pressure, disperse phase volume fraction, and initial emulsifier location (oil versus water phase) on particle size was examined. For both devices, the mean particle diameter decreased with increasing emulsifier concentration and homogenization pressure, and there was a linear log–log relationship between mean particle diameter and homogenization pressure. At a similar emulsifier level and homogenization pressure, dual-channel microfluidization produced smaller droplets and narrower distributions than single-channel microfluidization. This effect was attributed to a higher droplet disruption efficiency and/or lower droplet recoalescence rate for the dual-channel system. The dual-channel method could successfully produce nanoemulsions even at high oil concentrations (50%), whereas the single-channel method was only effective at producing nanoemulsions at relatively low oil concentrations (10%). This study demonstrates that dual-channel microfluidization is an efficient means of producing fine nanoemulsions with high oil loading levels, which may be advantageous for many commercial applications.

Effective rates of coalescence in oil–water dispersions under constant shear

We report destabilization of highly stable oil–water emulsion under shear. Prior studies on shear induced coalescence are restricted to lower volume fraction (up to 20%) of dispersed phase. In this contribution, the effect of shear induced coalescence in a larger range of volume fractions of dispersed phase, and shear rates, is presented. The experimental ranges have practical relevance in the context of industrial coalescers which exploit low shear to coalesce oil–water emulsions. For our work, a synthetic emulsion mimicking the properties of medium-heavy crude is subjected to simple shear. In summary, the studies reveal the effect of shear rate, volume fraction of dispersed phase and viscosity ratio on the evolving drop size distributions of oil phase. For low shear rates and volume fractions, the evolving drop size distributions show a bimodal distribution, while a multimodal nature of drop size population was observed for higher dispersed phase volume fraction (40%), something which has never been reported thus far. Finally, a population balance model employing diameter based coalescence kernel is used to rationalize the time evolution of droplet size distributions.

Rheology of Water-in-Oil Emulsions with Different Drop Sizes

Systemic experiments have been conducted to investigate the effect of drop sizes on the rheology of water-in-oil (W/O) emulsions. Three sets of emulsions with different average drop sizes were first prepared and then the corresponding rheologies were determined using a concentric viscometer. Results indicated that the flow behavior of concentrated emulsions changes qualitatively from Newtonian flow to non-Newtonian flow with shear rates. In Newtonian flow regime, a smaller drop size leads to a higher viscosity, and the increments are more pronounced at high dispersed phase volume fractions. Two local remarkable increases of the emulsion viscosity with dispersed phase volume fractions correspond to the percolation and glass-transition, respectively. In non-Newtonian flow regime, emulsions show shear-thinning behavior and can be fitted well by the power law model. For emulsions with volume fractions between 0.132 and 0.325, the flow index and consistency constant show power law relationship with the water content. Furthermore, the shear-thinning effect becomes stronger in the emulsions with smaller drop sizes. A correlation has been successfully developed for determining the clusters’ sizes in W/O emulsions and shows excellent agreement with the experimental data. As a consequence, a microscopic understanding (cluster level) was presented for the shear-thinning behavior of the emulsions in this study.

Shape memory effect and superelasticity in single crystals of iron-based alloys

It was demonstrated that in single crystals of disordered iron-based (Fe-28%Ni- 17%Co-11.5%Al-2.5%X (at. %) (X = Ti, Ta, Ti + Ta) alloys, which undergoing γ-α' thermoelastic martensitic transformation (γ - fcc - face-centered cubic lattice, α' - bct - body- centered tetragonal lattice), the precipitation of ordered γ'-phase particles at aged at 973 K for 0.5 h and 7 h results in the shape memory effect and superelasticity. It was experimentally discovered, that the both mechanical and functional properties - the shape memory effect and superelasticity - can be controlled by changing the chemical composition, the size and the volume fraction of dispersed particles of γ'-phase.

Effect of Temperature on the Shear-Thickening Behavior of Fumed Silica Suspensions.

Shear-thickening fluids (STFs) can be subjected to a significant temperature variation in many applications. Polymeric or oligomeric fluids are commonly used as suspending media for STFs. Because the viscosities of polymeric fluids are strongly temperature-dependent, large temperature changes can profoundly affect the shear-thickening responses. Here, the effect of temperature on the shear-thickening behavior of four low-molecular-weight polymeric glycols/fumed silica suspensions is reported. The dispersed-phase volume fraction, its surface chemistry, and the chemical compositions of the suspending media were varied. These factors influence the viscosity and the interactions between the suspended particles and the suspending media. Fumed silica particles with two different silanol-group surface densities were suspended in the polymeric glycols, where these silanol surface groups formed hydrogen bonds with the suspending media's glycols and internal oxygen atoms. Steady-shear experiments were performed over a temperature range spanning approximately 100 °C. The critical shear rate for the onset of shear thickening decreased with decreasing temperature. The critical shear rates were inversely proportional to the viscosity of the pure suspending media over these same temperature ranges. The response of STFs to varying both the temperature and shear rate investigated here will help to design application-specific STFs. Mitigation of a hypervelocity (6.81 km/s) impact on an aluminum facesheet sandwich composite filled with one of these STFs was demonstrated.

Fabrication of porous polyurethane monoliths on strengthening interface of concentrated emulsion polymerization

A method for preparing porous polyurethane (PU) monoliths through a step polymerization in concentrated emulsion template was proposed. The concentrated emulsion was constructed by using tolylene diisocyanate (TDI), butylenes glycol and a surfactant as the continuous phase, and deionized water as the dispersed phase. Polyglycerol polyricinoleate (PGPR) was selected as the surfactant because it was an amphiphilic oligomer containing reactive hydroxyl groups. It could react with TDI firstly and thus built up a solid interface to maintain the stability of the concentrated emulsion. As a result, polyurethane porous monolith was obtained by the curing reaction between TDI and –OH containing species and thereafter the removal of water phase. When colloidal silica particles were introduced into aqueous phase, a more uniform and finer porous structure could be achieved from the more strengthened interface. The effects of the composition, the surfactant, the volume fraction of dispersed phase, and the content of colloidal silica on the morphology of porous PU were investigated.

Modulus prediction of binary phase polymeric blends using symmetrical approximation systems as a new approach

In this study, a symmetrical approximation system (SAS) is proposed in order to predict Young’s modulus of polymer blend based on new geometrical approaches. The dominant morphologies of the blend (droplet-matrix and co-continuous) were simulated using comprehensive geometrical structures across the volume fraction range of dispersed phase. These morphologies were considered to be the dominant internal structures of the blend under percolation threshold and phase inversion point, respectively. However, between phase inversion point and percolation threshold a combination of both morphologies was assumed to form the dominant internal structure. This assumption led to dividing the volume fraction range of dispersed phase into four intervals and one phase inversion point. The co-continuous structure representative parameter (r) was calculated using R(D) factor which indicated the portion of co-continuous morphology in the blend structure resulted by increasing the volume fraction of dispersed phase after percolation threshold. Model parameter R representing droplet-matrix structure was evaluated using two different approaches to represent the best calculation procedure with best prediction of Young’s modulus. The geometrical structures of SAS model were designed to represent the most acceptable simulation of a blend system. Unlike other proposed models, SAS model provided the most compatible hypothetical structures with blend morphologies using appropriate and comprehensive geometrical foundations. Samples based on isotactic polypropylene and polyamide 6 were prepared in order to check the accuracy of SAS model. Furthermore, direct and independent approximation model and some other elicited data were also used in order to investigate the validity of SAS model.

Stabilization of highly concentrated emulsions with oversaturated dispersed phase: Effect of surfactant/particle ratio

Currently, there is considerable interest in highly concentrated emulsions (HCE) due to both the variety of rheological effects that are observed in their deformation and flow and to their practical application in the mining, pharmaceutical, cosmetics and food industries. The material investigated is highly concentrated water-in-oil emulsion with a dispersed phase volume fraction of approximately 90%. The dispersed phase is a super-cooled solution of inorganic salts. Instability of such emulsions arises either from crystallization of the dispersed phase in the system during ageing or under high shear conditions. Here, we report a new approach to stabilize this highly concentrated water-in-oil emulsion by adding colloidal particles in combination with short amphiphilic molecules. A series of five fumed silica nanoparticles, each with a different hydrophobicity index (HI) in the ranges 0.60–1.34 and >3, were mixed with sorbitan monooleate (SMO) into the oil phase prior to emulsification. The refinement time, rheological properties and stability of the resulting emulsions were investigated for varying SMO/particle ratios. At low surfactant-to-particle ratio, the silica content controls emulsion stability, but above some critical level (transitional point) SMO dominates over particles. The relationship between shear modulus and SMO-to-particle ratio shows the same transition point related to the same SMO-to-particle ratio found with the refinement time. Interestingly, for each HI, the emulsions are most stable in terms of both shelf life and under high shear when prepared with a SMO-to-particle ratio equaling exactly the value at this transitional point. Using the relationship between the zero modulus of particle dispersions in oil and the SMO-to-particle ratio, we show that the most stable emulsions are formed from dispersions having maximum particle flocculation, induced by SMO reverse micelles, in line with the SMO-to-particle ratio transitional point.

Characterization of stratification for an opaque highly stable magnetorheological fluid using vertical axis inductance monitoring system

A key requirement for the commercialization of various magnetorheological fluid (MRF)-based applications is sedimentation stability. In this study, a high viscosity linear polysiloxane (HVLP), which has been used for shock absorbers in heavy equipment, is proposed as a new carrier fluid in highly stable MRFs. The HVLP is known to be a thixotropic (i.e., shear thinning) fluid that shows very high viscosity at very low shear rate and low viscosity at higher shear rate. In this study, using the shear rheometer, the significant thixotropic behavior of the HVLP was experimentally confirmed. In addition, a HVLP carrier fluid-based MRF (HVLP MRF) with 26 vol. % was synthesized and its sedimentation characteristics were experimentally investigated. But, because of the opacity of the HVLP MRF, no mudline can be visually observed. Hence, a vertical axis inductance monitoring system (VAIMS) applied to a circular column of fluid was used to evaluate sedimentation behavior by correlating measured inductance with the volume fraction of dispersed particles (i.e., Fe). Using the VAIMS, Fe concentration (i.e., volume fraction) was monitored for 28 days with a measurement taken every four days, as well as one measurement after 96 days to characterize long-term sedimentation stability. Finally, the concentration of the HVLP MRF as a function of the depth in the column and time, as well as the concentration change versus the depth in the column, are presented and compared with those of a commercially available MRF (i.e., Lord MRF-126CD).

Numerical study of turbulent liquid‐liquid dispersions

A numerical approach is developed to gain fundamental insight in liquid‐liquid dispersion formation under well‐controlled turbulent conditions. The approach is based on a free energy lattice Boltzmann equation method, and relies on detailed resolution of the interaction of the dispersed and continuous phase at the microscopic level, including drop breakup and coalescence. The capability of the numerical technique to perform direct numerical simulations of turbulently agitated liquid‐liquid dispersions is assessed. Three‐dimensional simulations are carried out in fully periodic cubic domains with grids of size . The liquids are of equal density. Viscosity ratios (dispersed phase over continuous phase) are in the range 0.3–1.0. The dispersed phase volume fraction varies from 0.001 to 0.2. The process of dispersion formation is followed and visualized. The size of each drop in the dispersion is measured in‐line with no disturbance of the flow. However, the numerical method is plagued by numerical dissolution of drops that are smaller than 10 times the lattice spacing. It is shown that to mitigate this effect it is necessary to increase the resolution of the Kolmogorov scales, such as to have a minimum drop size in the range 20–30 lattice units [lu]. Four levels of Kolmogorov length scale resolution have been considered , 2.5, 5, and 10 [lu]. In addition, the numerical dissolution reduces if the concentration of the dispersed phase is increased. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2618–2633, 2015

Influence of emulsification process on the properties of Pickering emulsions stabilized by layered double hydroxide particles.

This paper reports the influence of emulsification process on the packing of layered double hydroxide (LDH) particles at the aqueous/oil phase interface and the properties of the resulting Pickering emulsions. Emulsions prepared by ultrasonication display superior long-term stability and gel-like characteristics at the dispersed phase volume fraction well below the random close packing limit, whereas emulsions with same compositions prepared by vortex mixing show some extent of sedimentation and liquid-like behaviors. Rheological measurements demonstrate that the zero-shear elastic modulus and yield stress of gel-like emulsions exhibit power-law dependences on particle concentration and independence on aqueous/oil phase ratio. The microstructural origin of this behavior is investigated by optical microscopy, revealing the droplets become strongly adhesive and a heterogeneous percolating network is formed among neighboring droplets. Fluorescent confocal microscopy measurements further confirm that the droplet adhesion is due to particle layers bridging opposite interfaces. In contrast, homogeneous, isolated, and densely packed droplets are present in emulsions prepared by vortex mixing, which results in these systems being dominantly viscous like the suspending fluid. This study shows that the emulsification process can be used as a trigger to modify long-term stability and rheology of solid-stabilized multiphase mixtures, which greatly expands their potential technological applications.

Experimental study on the dispersed phase macro-mixing in an immiscible liquid–liquid stirred reactor

The spatial nonuniformity of solute concentration in the dispersed phase of immiscible liquid–liquid dispersion is smeared out by coalescence and breakup of drops, which has a very significant effect on the productivity of relevant chemical processes. Novel experiments have been designed to visualize and quantify accurately the macro-mixing within the dispersed phase using the planar laser induced fluorescence (PLIF) method combined with a refractive index matching technique in this work. Batch experiments are carried out in a stirred reactor for an electrolytic solution dispersed in silicone oil. It is revealed that the dispersed phase macro-mixing behavior differs much from that of the continuous phase of multiphase systems and is heavily dependent upon the drop interaction rate and thus power consumption. The dispersed phase mixing time decreases with the increase of the dispersed phase volume fraction. Dispersed phase mixing time varies inversely with the power consumption per unit volume dispersion. The effect of impeller type on the dispersed phase mixing time is greatly different from that on the continuous/single phase mixing time. The effect of radial impeller clearance on the dispersed phase mixing time is contrary to that on the continuous/single phase mixing time.

Deformation Behavior of the Percolating Eutectic Intermetallic in HPDC and Squeeze-Cast Mg Alloys

The structural compliance of the spatially interconnected intermetallic network in a squeeze-cast MRI230D alloy was determined using focused ion beam (FIB) data and finite element (FE) modeling, and compared with data for a high-pressure die-cast AZ91D and three binary Mg-RE alloys from the existing literature. The respective elastic responses were sorted out into two characteristic behaviors: for eutectic volume fractions less than ~22% the behavior was akin to that of highly compliant, bending-dominated structures, whereas for larger fractions, it reproduced that of structurally efficient, stretch-dominated microtruss structures. In all cases, the contribution from the interconnected network added to the total strength of the alloy an amount comparable with the strengthening expected from a similar volume fraction of dispersed particles. Being more compliant, the bending-dominated structures appeared less prone to developing damage by cracking at low strains than the stretch dominated ones.

Influence of emulsifier concentration on nanoemulsion gelation.

Nanoemulsion gels are a new class of soft materials that manifest stronger elasticity even at lower dispersed phase volume fraction. In this work, gelation in 40 wt % canola oil-in-water nanoemulsions was investigated as a function of emulsifier type (anionic sodium dodecyl sulfate (SDS) or nonionic Tween 20) and concentration. It was observed that the liquid nanoemulsions transformed into viscoelastic gels at a specific concentration range of SDS, whereas no gelation was observed for Tween 20. The apparent viscosity, yield stress, and storage modulus of the nanogels increased with SDS concentration until 15 times critical micelle concentration (CMC), thereafter decreased steadily as the gelation weakened beginning 20 CMC. Three regimes of colloidal interactions in the presence of emulsifier were proposed. (1) Repulsive gelation: at low SDS concentration (0.5-2 times CMC) the repulsive charge cloud around the nanodroplets acted as interfacial shell layer that significantly increased the effective volume fraction of the dispersed phase (ϕ(eff)). When ϕ(eff) became comparable to the volume fraction required for maximal random jamming, nanoemulsions formed elastic gels. (2) Attractive gelation: as the SDS concentration increased to 5-15 times CMC, ϕ(eff) dropped due to charge screening by more counterions from SDS, but depletion attractions generated by micelles in the continuous phase led to extensive droplet aggregation which immobilized the continuous phase leading to stronger gel formation. (3) Decline in gelation due to oscillatory structural forces (OSF): at very high SDS concentration (20-30 time CMC), structural forces were manifested due to the layered-structuring of excess micelles in the interdroplet regions resulting in loss of droplet aggregation. Tween 20 nanoemulsions, on the other hand, did not show repulsive gelation due to lack of charge cloud, while weak depletion attraction and early commencement of OSF regime leading to liquid-like behavior at all concentrations. The nanogels possess great potential for use in low-fat foods, pharmaceuticals and cosmetic products.

PEG 400/Paraffin oil non‐aqueous emulsions stabilized by PBut‐Block‐P2VP block copolymers

ABSTRACTFor the preparation of PEG 400 in paraffin oil non‐aqueous biocompatible emulsions, the stabilization efficiency was compared for two well‐defined poly(butadiene)‐block‐poly(2‐vinylpyridine) (PBut‐block‐P2VP) block copolymers, with similar molecular weights but different compositions. The PBut128‐block‐P2VP50 and PBut189‐block‐P2VP37 samples, designated as copolymer A and B, respectively, are self‐organized in paraffin oil as micelles with a P2VP core and a PBut corona. The PEG 400/paraffin oil emulsion characteristics were determined as a function of the copolymers concentrations and phase ratios. Higher static and shear stabilities were obtained for emulsions stabilized by copolymer B than for those obtained in the presence of copolymer A. A further difference concerns the droplet size, relative viscosity, and loss modulus values obtained at a given dispersed phase volume fraction. At constant copolymer concentrations, it appeared that copolymer B, with a longer PBut sequence, is a more efficient emulsifier and stabilizer than copolymer A. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41390.

Justification of the drift-flux model for two-phase flow in a circular pipe

A flow of a gas-liquid dispersed mixture in a circular pipe with a variable inclination to the horizon, as applied to oil and gas flows in wells, is considered. Within the framework of a multi- fluid approach, the equations of an asymptotic drift-flux model, which contains an algebraic relation between the phase velocities and one momentum equation for the volume-averaged velocity of the mixture, are derived. It is shown that the drift-flux model in this formulation strictly follows from the balance laws under assumption of inertialess velocity slip of the phases in case of validity of one of the following conditions: (i) the dispersed-phase volume fraction is small; (ii) the phase velocity slip may be neglected; or (iii) the flow regime is inertialess and the acceleration of the mixture can be neglected. A numerical algorithm based on the SIMPLE method is implemented for solving the obtained equations of the drift-flux model. The possibility of modeling the gravitational segregation and the pressure buildup in a shut-in well and transient slug flows is demonstrated.

Porous materials with tunable mechanical properties

We present a study of the mechanical properties of porous polymer materials elaborated from the controlled formulation of emulsions and using a polyHIPE templating approach. This consists in the polymerization of high internal phase water-in-oil emulsions of controlled average size and dispersed phase volume fraction. We investigate the evolution of the linear and non-linearmechanical properties as a function of two sets of parameters, that define the structure (namely pore size and volumefraction) and the composition (chemical composition of the polymer walls) of the material.

Modeling the influence of interaction layer formation on thermal conductivity of U–Mo dispersion fuel

The Global Threat Reduction Initiative Program continues to develop existing and new test reactor fuels to achieve the maximum attainable uranium loadings to support the conversion of a number of the world’s remaining high-enriched uranium fueled reactors to low-enriched uranium fuel. Currently, the program is focused on assisting with the development and qualification of a fuel design that consists of a uranium–molybdenum (U–Mo) alloy dispersed in an aluminum matrix. Thermal conductivity is an important consideration in determining the operational temperature of the fuel and can be influenced by interaction layer formation between the dispersed phase and matrix, porosity that forms during fabrication of the fuel plates or rods, and upon the concentration of the dispersed phase within the matrix. This paper develops and validates a simple model to study the influence of interaction layer formation, dispersed particle size, and volume fraction of dispersed phase in the matrix on the effective conductivity of the composite. The model shows excellent agreement with results previously presented in the literature. In particular, the thermal conductivity of the interaction layer does not appear to be as important in determining the effective conductivity of the composite, while formation of the interaction layer and subsequent consumption of the matrix reveals a rather significant effect. The effective thermal conductivity of the composite can be influenced by the dispersed particle distribution by minimizing interaction layer formation and preserving the higher thermal conductivity matrix.