Dispersed Phase Volume Research Articles

Rheology and Small-Angle Neutron Scattering as Tools for Evaluating Emulsification. Application to Reverse Highly Concentrated Fluorinated Emulsions

An emulsion is a dispersion of one fluid in another nonmiscible fluid, stabilized by a surfactant. Such a mixture is not at thermodynamic equilibrium, and some energy is needed to create the unfavorable interface. This energy is provided by a mechanical stirring. Due to the preparation process, the surfactant is shared among the oil/water interface (droplets surface) and the continuous phase. In this paper, we estimate the emulsification rate in relation with both the dispersed phase volume fraction and the mechanical stirring. For low volume fraction, this rate is very low showing that the mechanical stirring is inadequate, whereas it becomes more efficient (but still insufficient) for higher volume fractions. Using small-angle neutron scattering under shear and rheological measurements, we follow the surfactant distribution when applying a steady flow: small shear flows help the aging whereas high shear flows improve the fragmenting and hence the emulsification.

Effect of temperature on the ultrasonic properties of oil-in-water emulsions

The influence of temperature on the ultrasonic properties of oil-in-water emulsions was investigated. The ultrasonic velocity and attenuation coefficient of a series of corn oil-in-water emulsions with different disperse phase volume fractions ( φ=0 to 0.5) and mean droplet radii ( r=0.1 to 0.5 μm) were measured as a function of temperature (5 to 50°C). These measurements were in reasonable agreement with predictions made using ultrasonic scattering theory. The ultrasonic velocity of the emulsions was particularly sensitive to their composition, temperature and droplet size. Around 15°C, the ultrasonic velocity was fairly insensitive to oil concentration. Below this temperature, it increased with oil concentration, whilst above this temperature it decreased. The ultrasonic velocity increased with droplet size. The attenuation coefficient of the emulsions was much more sensitive to composition and droplet size, rather than temperature. It increased with oil concentration and decreased with temperature. The implications of these results for the use of ultrasound for determining the size distribution and concentration of droplets in emulsions are investigated.

Phase inversion studies in liquid‐liquid dispersions

AbstractA study of the phase inversion behavior of liquid‐liquid dispersions in stirred vessels is performed for liquids of various physical properties at various operating conditions. Physical parameters studied are density (867 to 1180 kg/m3), viscosity (0.00096 to 0.00378 Pa·s), and interfacial tension (0.0089 to 0.0323 N/m). Ambivalence region plots are presented and compared with results reported in the literature. Experiments are performed to examine the effects of impeller type and impeller‐to‐tank diameter ratio (D/T) on the ambivalence behavior. Also, phase inversion time experiments are performed to investigate the time required for complete phase inversion under various dynamic conditions. The traditional method of plotting the organic phase volume fraction at phase inversion against the agitation speed at that condition is compared with the method of plotting the initially dispersed phase volume fraction at phase inversion against the agitation speed at that condition. A hysteresis phenomenon is shown in phase inversion from O/W to W/O and W/O to O/W dispersions. Also, it is shown that, depending on the physical properties of the dispersed and continuous phases, phase inversion may occur when the agitation speed is increased or decreased.

Low Hydrophobically Modified Poly(Acrylic Acid) Stabilizing Macroemulsions: Relationship between Copolymer Structure and Emulsions Properties

Low hydrophobically modified (with dodecylamide chain) linear poly(acrylic acid) sodium salts (LHMPAANa) of various degrees of grafting (τ) and molecular weights were synthesized and used as emulsifiers of then-dodecane/water (NaNO310−3M) system. Stability and flow properties of the resultingn-dodecane in water emulsions (dispersed phase volume fraction = 0.5) were investigated as a function of τ (τ = 0 to 10% in mol), molecular weight (5000, 50,000, and 150,000 g/mol) and polymer concentration (0 to 10%). It was clearly shown that viscosification (via an associating mechanism of LHMPAANa) of the external phase of emulsions is a key factor in explaining dispersion breakdown. However, a complete description of the phenomenon could not be achieved without considering the adsorption of the polymer at the liquid-liquid interface which depends closely on τ but not much on molecular weight. The molecular weight effects were found to be restricted to the viscosification of the outer phase.

脱灰石炭造粒粒子の解砕による石炭‐重油‐水混合物の流動特性

The flow characteristics of coal-oil-water mixture (COW) was investigated. COW was prepared by a disintegration of deashed coal agglomerates, which were obtained by the oil agglomeration of coal. When the volume fraction of dispersed waterdrops in COW was smaller than 0.2, the dispersed waterdrops influenced the flow characteristics of COW to the same extent as the dispersed coal particles. COW behaved as Bingham fluid. Both the yield value and Bingham viscosity increased with increasing total disperse phase volume fraction in COW, and with decreasing temperature. The relative viscosity of COW was well correlated by the equation derived with reference to Mooney's equation.

Numerical Simulation of Ostwald Ripening in Emulsions

Ostwald ripening at finite dispersed phase volumes was modeled successfully using linearized analytical solutions of the ripening equations and an explicit numerical routine. The numerical approach incorporated a number frequency distribution of drop radii rather than using a discrete number of drops. The effect of finite dispersed phase volume fraction was accounted for by using half the average separation distance between drops as the mass transfer boundary. The numerical predictions matched analytical predictions for infinitely dilute systems almost exactly and were in qualitative agreement with analytical predictions for infinitely concentrated systems. The numerical model was applied to the full range of dispersed phase concentrations and successfully predicted experimental cumulative frequency distributions. The growth rate, i.e. the change in the cube of the mean radius with time, was confirmed to be constant at any dispersed phase volume fraction. A simple expression was developed relating growth rate to dispersed phase volume fraction. Predicted growth rates at dispersed phase volume fractions less than 0.2 matched those found experimentally and by other numerical methods. Predicted growth rates at higher dispersed phase volume fractions agreed well with experimental data from the literature but were significantly higher than predictions from other numerical methods.

Prediction of settling velocity of drops in a concentration batch liquid‐liquid dispersion

AbstractA simple and new model for the prediction of drop velocity as a function of dispersed phase volume fraction has been proposed on the basis of experimental knowledge of onset time of complete separation between two phases as function of the initial hold‐up.

Microstructure analysis at the percolation threshold in reverse microemulsions

Time domain dielectric spectroscopy of reverse water/acrylamide/Aerosol-OT (AOT)/toluene microemulsions shows that percolation induced by increasing cosurfactant concentration (increasing cosurfactant chemical potential) obeys scaling above and below a percolation threshold. This scaling analysis suggests that the observed percolation is close to static percolation limits. Self-diffusion measurements derived from nuclear magnetic resonance pulsed-gradient spin-echo experiments reveal an increase in water proton diffusion above the percolation threshold. This increase is assigned to water transport through fractally chained assemblies of microemulsion droplets. The diffusion of water, cosurfactant, and surfactant (AOT) below threshold is modeled quantitatively taking into account the chemical partitioning equilibria between the microemulsion droplets and the toluene continuous pseudophase. Above threshold, the apparent increasing water and cosurfactant partitioning into the toluene (continuous) pseudophase suggests facilitated transport through fractal aggregates. A dynamic partitioning model is used to estimate the volume of percolating fractal clusters, and yields an order parameter for water-in-oil to percolating cluster microstructural transitions. This same order parameter is also illustrated to derive from self-diffusion data wherein percolation and transformation to sponge phase microstructure are driven by increases in temperature and in disperse phase volume fraction. For microstructural transitions driven by three different field variables, chemical potential, temperature, and disperse phase volume fraction, this order parameter shows that the onset of percolation corresponds to the onset of increasing water proton self-diffusion, and that the onset of increasing surfactant self-diffusion corresponds to the formation of bicontinuous microstructures and the onset of transformation to middle phase microemulsion.

Characteristics of antibiotic production in a multiphase system

The production of an extracellular antibiotic, actinorhodin, was investigated in a 2-litre bench-top bioreactor. In order to determine the behaviour of Streptomyces coelicolor cells in a two liquids system, a perfluorocarbon (PFC), which is an oxygen carrier, was added to the fermentation medium. The presence of 50% (v/v) PFC in the fermentation medium resulted in a five-fold increase in the final antibiotic concentration. As a result of the importance of drop size distribution and the liquid-liquid interfacial area in such multiphase systems, the effects of dispersed phase (PFC phase) volume fraction on size distribution and on interfacial area were investigated. The results showed that the size distribution was positively skewed and that the liquid-liquid interfacial area increased with increasing PFC concentration. The liquid-liquid interfacial area was proportional to PFC concentration to the power 1·53.

Flow rate measurement by kinematic wave detection in vertically upward, bubbly two-phase flows

This paper describes a technique for measuring the flow rates of both phases in one-dimensional, vertically upward, bubbly oil–water flows. Measurements of the speed of naturally occurring kinematic waves, obtained using an impedance cross-correlation flow meter, were combined with measurements of the disperse phase volume fraction and an appropriate kinematic wave model to yield predictions of the flux density of both the oil and the water. A systematic error of −3.16%, and an additional random error with a standard deviation of 2.58%, was observed in the predicted oil flux density (and the predicted oil volumetric flow rate). A systematic error of +4.41%, and an additional random error with a standard deviation of 4.83%, was observed in the predicted water flux density (and the predicted water volumetric flow rate). The impedance cross-correlation flow meter has no moving parts and is of robust construction, making the technique described here suitable for implementation in vertical oil wells.

Flow of Liquid/Liquid Dispersions in a Hele-Shaw Cell.

Flow of liquid/liquid dispersions have been investigated in a Hele-Shaw cell which contained a thin disk held between two parallel plates. This device offers a well defined flow field and also permits visual observation of the dispersed drop movement. The dispersed drops coalesce with the disk for the systems where the dispersed phase wets the disk surface. The dispersed phase accumulate at the downstream end of the disk and they detach from there as blobs. Through an accurate measurement of accumulated dispersed phase volume, the coalescence rate was determined. The coalescence efficiency in the Hele Shaw cell is determined by dividing the coalescence rate by the undisturbed flow rate of the dispersed phase through an area equal to the projected area of the disk on a plane normal to the flow direction. The coalescence efficiency first increases and then decreases with the flow rate of dispersion. The coalescence rate/disk dimensions increases with the decrease in the disk dimensions. The rate of coalescence increases with the increase in the dispersed drop diameter and it decreases with the increase in the continuum phase viscosity. The presence of surfactants reduces the coalescence rate. All these results are quantitatively explained through a model, which takes into account several important features like various mechanism of drainage, the roles of dispersion and continuous phase viscosities, and the drop deformation.

Effect of processing parameters on the properties of peptide-containing PLGA microspheres

The physico-chemical properties of biodegradable polylactide-co-glycolide (PLGA) microspheres containing the peptide salmon calcitonin (sCT) were affected by the processing parameters. The microsphere size increased with an increase in the viscosity of the polymer solution. Concentration of methanol and peptide in the dispersed phase had the most discernible effects with the combination causing external and internal porosity. Increasing sCT in the presence of methanol increased the surface area and porosity. The surface area also increased as the molecular weight of the polymer was decreased. At higher ratios of the dispersed phase volume to the continuous phase volume, the surface area and surface porosity were higher and the particle size was lower. Thus, the physico-chemical properties of the microspheres can be easily altered by varying the processing parameters allowing formation of microspheres with a range of properties. The microspheres may be used to evaluate the relationship between the properties and ultimate in-vivo performance.

Rheological behavior of an aluminum nitride nanoparticle suspension in Poly(amic acid)-nmp system

ABSTRACTPreliminary rheological characterizations of aluminum nitride (AIN) nanoparticle suspensions in nonaqueous Newtonian fluid media, NMP and NMP/poly(amic acid) solutions, reveal marked differences in viscoelastic behavior, at relatively low dispersed phase volume fractions. Dynamic mechanical and steady shear measurements provide experimental evidence of the effective interparticle and polymer/particle interactions in a dispersion process of nonoxide nanoparticles for ceramic/polymer nanocomposites. The rheological nature of the nanoparticle suspensions corresponds to interparticle physicochemical interactions that have been previously concluded and discussed.

About entangled networks of worm-like micelles: a rejected hypothesis

We report new results from small-angle neutron scattering ond12-cyclohexane/lecithin/water micellar solutions performed as a function of the water content (w0), temperature (T) and dispersed phase volume fraction (ϕ). The data from dilute samples are interpretable in terms of the existence of giant cylindrical reverse micelles and are well fit with a core-shell model (that provides the micelle structure and dimensions) with values of 28 and 45 A for the inner core and the outer shell radii, almost independent on temperature and concentration. Such a result could appear consistent with the current idea that worm-like micelles are living polymers. On the contrary, the appearance of a sharp interference maximum at high concentrations (ϕ>0.15) suggests arguments against the current hypothesis of an entangled network of giant flexible cylinders. Further arguments against the current hypothesis are given by the close similarity between the above described results and those from free of water micelles (for sure not cylinders). All the data are well fitted in terms of a unique model taking into account the micellar form factor plus a hard sphere structure factor. The data analysis suggests a micellar size distribution determined by the competition between concentration and interaction effects on which temperature plays not a minor role. Following our results, the current hypothesis of a gel structure in terms of an entangled network can be assumed as wrong and some caution has to be taken in assuming wormlike micelles as living polymers.

Rate and temperature dependence of fracture toughness in ABS resins in relation to dispersed-phase structure

The paper compares the fracture behaviour of two ABS terpolymers having the same glassy matrix and similar dispersed phase volume, but different amounts of glassy sub-inclusions in the rubbery particles. The fracture toughness of the two materials showed similar strain rate dependence, but different temperature dependence. The results are interpreted in terms of different deformation mechanisms occurring at the failure zone ahead of the crack tip.

Small-Angle Neutron Scattering Investigations of Liquid−Liquid Phase Separation in Heterogeneous Linear Low-Density Polyethylene

The issue of multiple equilibrium phases in compositionally heterogeneous random copolymers has been addressed by a series of small-angle neutron scattering (SANS) experiments. An ethylene−hexene (EH) copolymer, representative of many linear low-density polyethylenes (LLDPE) has been shown to contain a dispersed minority phase (volume fraction, φ ∼ 0.02) consisting of highly branched, amorphous material. The dispersed phase is eliminated to a good approximation by xylene extraction, which removes the low molecular weight and highly branched molecules. The extracted material contains a much higher fraction of branched molecules and hence has a greater proportion of the dispersed phase (φ ∼ 0.2). These findings support the prediction of liquid−liquid phase separation for compositionally polydisperse LLDPEs, whereby the more highly branched molecules in the distribution may phase segregate, even if the overall branch content is low.

Ultra-High Resolution Small-Angle Neutron Scattering Investigations of Liquid-Liquid Phase Separation in Linear Low-Density Polyethylene

ABSTRACTPrevious small-angle neutron scattering (SANS) studies [1] of heterogeneous ethylene-hexene linear low-density polyethylene (LLDPE) copolymers have confirmed the existence of a dispersed minority phase (volume fraction φ ∼ 10−2) consisting of highly branched, amorphous material. However, these experiments were conducted via a pinhole SANS spectrometer with an upper resolution limit ∼ 103 Å, whereas microscopy indicates that the dimensions of the disperse phase extend to the μm-range. We have therefore complemented these investigations via a Bonse-Hart ultra-small angle neutron scattering (USANS) instrument which increases the instrumental resolution in reciprocal space by a factor - 100, and thus particle size up to 30 μm can be resolved. The sensitivity of the USANS camera has recently been increased by two orders of magnitude by using the modified channel cut crystals [2], and the performance is therefore comparable to the best x-ray Bonse-Hart cameras. Xylene extraction removes the highly branched molecules and hence the volume fraction of the disperse phase is higher (φ ∼ 0.3) in the extracted material.

Direct contact heat transfer between two immiscible liquids flowing in a horizontal concentric annulus

Direct contact heat transfer between water and a heat transfer oil was investigated under non-boiling conditions in co-current turbulent flow through a horizontal concentric annulus. The ratio of the inner pipe diameter to the outer pipe diameter (aspect ratio) κ = 0.730−0.816; total liquid velocity (mixture velocity) V T = 0.42−1.1 m/s; inlet oil temperature T oi = 38−94°C; oil volume fraction in the flowing mixture φ o = 0.25−0.75 were varied and their effects on the overall volumetric heat transfer coefficient U v were determined at constant interfacial tension of 48 dynes/cm. It was found that, in each concentric pipe set, the overall volumetric heat transfer coefficient increased with increasing dispersed phase volume fraction at each constant mixture velocity and reached a maximum at around φ o = φ w ≈ 0.5. The maximum U v values increased with increasing total liquid velocity and decreasing aspect ratio of the annulus. The volumetric heat transfer coefficient was also found to increase with increasing inlet oil temperature and increasing total liquid velocity but to decrease with length along the test section keeping all other parameters constant. Empirical expressions for the volumetric heat transfer coefficient were obtained within the ranges of the experimental parameters.

Toughening of vinyl ester resins with modified polybutadienes

This study is of toughening some vinyl ester resins with low-molecular-weight butadiene-based polymers. Liquid polybutadiene and copolymers with acrylonitrile are immiscible with the commonly used vinyl ester resin, Derakane 411-45. Despite this incompatibility, some toughening is seen in blends with this vinyl ester resin. Modification of hydroxy-terminated polybutadiene through reaction with a diisocyanate and various alcohols renders the polymer more compatible but not miscible with the resin. With increasing length of the end-groups, the ability to provide a tougher cured resin improves such that the energy to propagate a slow crack increases more than 10 times. Addition of 5 wt% of a butadiene polymer resulted in a disperse-phase volume fraction greater than 10%. Blends with Derakane 411-45 showed greater toughness than that of the toughened resin Derakane 8084, which was also improved by addition of butadiene copolymers.

Drop size distributions in high holdup fraction dispersion systems: effect of the degree of hydrolysis of PVA stabilizer

Although turbulence-stabilized dispersions are of considerable industrial importance, their behaviour is generally not well understood, especially for the high dispersed phase volume fractions encountered in suspension polymerization reactors. The dispersion is formed by two dynamic processes, namely, drop breakage and coalescence. Breakage mainly occurs in regions of high shear stress near the impeller or as a result of turbulent velocity and pressure fluctuations along the surface of a drop. Droplet coalescence is prevented by the combined action of turbulent agitation and the addition of protective colloids such as poly(vinyl alcohol) (PVA). Depending on the combination of the degree of agitation and the concentration and type of surface active agent, the average droplet size can exhibit a U-shaped variation with respect to the impeller speed or the degree of hydrolysis of the PVA stabilizer. This U-type behaviour has been confirmed both experimentally and theoretically and has been attributed to a manifestation of the balance between breakage and coalescence rates of the monomer drops. Both processes are related to the interfacial tension and its variation with time as a result of the varying polymer concentration and conformation at the monomer/water interface. In the present study, a series of experiments were carried out with a model system of 50% n-butyl chloride in water in the presence of PVA with varying degrees of hydrolysis at different agitation rates. A generalized numerical algorithm incorporating the most comprehensive models describing the breakage and coalescence processes has been used for simulating the steady-state drop size distributions in a high holdup liquid—liquid dispersion system in order to elucidate the breakage and coalescence mechanisms as a function of the droplet interfacial characteristics. It is shown that the model simulations are in satisfactory agreement with measurements of the drop size distributions over the whole range of the experimental conditions investigated.