Phase Inversion Point Research Articles

The co-continuous morphology of biocompatible ethylene-vinyl acetate copolymers/poly(ε-caprolactone) blend: effect of viscosity ratio and vinyl acetate content

The phase behavior and its linear viscoelastic responses of a biocompatible blend based on ethylene-vinyl acetate copolymers and poly(e-caprolactone) (EVA/PCL) were studied in this work in terms of blending ratios and annealing. The effects of viscosity ratios and vinyl acetate contents of the EVA on the co-continuous morphology were addressed. The results show that EVA/PCL is a typical immiscible blend due to the high interfacial tension between the two polymers. Thus, the blend shows a wide percolation range with a narrow fully co-continuous region. Although the phase inversion point can be well predicted by the viscous Utracki model, the dynamic viscoelastic responses of the blend cannot be well described by the emulsion model. The elasticity ratio was proposed to play an important role together with the viscosity ratio on the phase inversions. During dynamic annealing, the phase size of both the sea–island and the co-continuous structures increases evidently, but the principle of time–temperature superposition is only valid for the co-continuous blend while fails with that with the sea–island phase structure. Beside, the phase size of the co-continuous structure is dependent strongly on the viscosity ratio between EVA and PCL. With reduced viscosity ratio, the phase size increases remarkably. However, vinyl acetate (VA) contents of the EVA have little influences on the interfacial properties and phase size of the co-continuous blends in the experimental content ranges (28–12 wt.%).

Morphology development and phase inversion during dynamic vulcanisation of EPDM/PP blends

Morphology development and phase inversion were investigated during dynamic vulcanisation of ethylene–propylene–diene terpolymer (EPDM)/polypropylene (PP) blends. The effects of viscosity ratio and cross-linking reactions were also addressed. EPDM/PP blends were dynamically vulcanised in a Haake batch mixer using resole and SnCl 2 as cross-linking agents. The morphology development and cross-linking degree with reaction time were followed by morphology analysis (SEM and TEM) and measurement of EPDM gel content, respectively. For the same reaction time, it was found that the EPDM gel content decreased when the low-molecular-weight EPDM was used. As a result, the morphological development was delayed and the phase-inversion point was shifted to higher reaction times, allowing us to monitor morphological development during a thermoplastic vulcanisate (TPV) preparation. Using the low-molecular-weight EPDM and increasing the PP viscosity accelerated the morphological development, shifting phase-inversion to lower reaction times. While blend composition influenced final TPV morphology, it had a minor effect on the mechanism of morphological development. A correlation between cross-linking degree and morphology development was established. The results obtained allowed to propose a mechanism of morphology development during dynamic vulcanisation of the EPDM/PP blends, including phase inversion.

Viscous Oil Emulsification by Catastrophic Phase Inversion: Influence of Oil Viscosity and Process Conditions

This study deals with the description of the influence of oil viscosity and process conditions on catastrophic phase inversion, through the analysis of the effects of formulation and process variables on the dispersed phase fraction at which the inversion is triggered. The in situ simultaneous follow-up of viscosity and conductivity measurements allowed, from a process point of view, to emphasize the effect of the aqueous phase addition rate on the catastrophic phase inversion point (PIP) and multiple w/O/W emulsion formation. Thus if the aqueous phase is added by very small fractions, formulation dominates and the inversion phenomenon can be accelerated, as a consequence of multiple emulsion formation, that greatly increases the volume of effective dispersed phase. An increase in oil viscosity greatly increased the tendency of the oily phase to become the dispersed phase and promoted the formation of highly concentrated emulsions (about 80 to 95% in volume) after inversion.

Flux dependent oil permeation in the ultrafiltration of highly concentrated and unstable oil-in-water emulsions

The performance of a 300kD UF membrane in separating highly concentrated and unstable O/W emulsions up to their phase inversion point was studied in this work. The membrane system was operated at constant fluxes ranging from 10 to 60lmh. The flux vs. trans-membrane pressure relationship was used to determine the critical flux based on pressure. The oil concentration in the permeate as a function of flux was used to determine a critical flux based on oil penetration. The values of the critical fluxes, as determined by these two methods, were approximately equal. Separation efficiencies of 99.5% at fluxes below the critical flux were obtained. It was identified that the relationship between the critical flux for oil passage at 0.2wt% oil vs. the concentration of oil in the emulsion was linear with an intercept corresponding to the phase reversal point. The filter cake at the surface of the membrane was found to be compressible with a pressure dependence ranging from 0.5 to 0.7. The oil breakthrough analysis indicated that the cake at the surface of the membrane had a noticeable yield stress similar to a Bingham fluid. The flux and oil permeation results were also explained based on the colloidal glass transition point of the oil droplets in the filter cake at the surface of the membrane. For highly concentrated, unstable, oil emulsions, operating at fluxes above the critical flux involves a penalty above that of increased pressure requirements that is reflected by a reduction in the separation efficiency of the membrane.

ChemInform Abstract: Positive-Temperature-Coefficient Effect in Graphite-Cristobalite Composites.

An anomalous positive temperature coefficient (PTC) of resistance was found in a conductor-insulator ceramic composite. The composite material was composed of randomly dispersed conducting graphite and insulating cristobalite-form SiO 2 particles. The PTC effect occurred at exactly 230 o C, that is, at a reversible phase inversion point with a large thermal expansion of cristobalite. The magnitude of the PTC anomaly was high in composites located in the middle of the percolation curve, and loaded with large graphite and fine SiO 2 particles

Investigations of phase inversion and frictional pressure gradients in upward and downward oil–water flow in vertical pipes

The present study has attempted to investigate phase inversion and frictional pressure gradients during simultaneous vertical flow of oil and water two-phase through upward and downward pipes. The liquids selected were white oil (44 mPa s viscosity and 860 kg/m 3 density) and water. The measurements were made for phase velocities varying from 0 to 1.24 m/s for water and from 0 to 1.87 m/s for oil, respectively. Experiments were carried either by keeping the mixture velocity constant and increasing the dispersed phase fraction or by keeping the continuous phase superficial velocity constant and increasing the dispersed phase superficial velocity. From the experimental results, it is shown that the frictional pressure gradient reaches to its lower value at the phase inversion point in this work. The points of phase inversion are always close to an input oil fraction of 0.8 for upward flow and of 0.75 for downward flow, respectively. A few models published in the literature are used to predict the phase inversion point and to compare the results with available experimental data. Suitable methods are suggested to predict the critical oil holdup at phase inversion based on the different viscosity ratio ranges. Furthermore, the frictional pressure gradient is analyzed with several suitable theoretical models according to the existing flow patterns. The analysis reveals that both the theoretical curves and the experimental data exhibit the same trend and the overall agreement of predicted values with experimental data is good, especially for a high oil fraction.

Characteristics of impact modified polystyrene/organoclay nanocomposites

The poor impact resistance of Polystyrene (PS) was enhanced by the addition of elastomeric material, SEBS-g-MA. To prevent the reduction in strength and stiffness, organoclay Cloisite® 25A was used as filler and introduced into the matrix by a corotating twin screw extruder. Throughout the study, the clay content was kept at 2 wt%, whereas the content of SEBS-g-MA was varied between 5 and 40 wt%. It was found that Cloisite® 25A displays well dispersion in the ternary nanocomposites and the degree of dispersion increases with the elastomer content. The elastomeric phase has a greater viscosity than pure PS. Thus, as expected, at low elastomer contents, it forms the dispersed phase in the matrix as droplets. Transmission electron microscopy results show that the clay layers reside at the interphase between PS and elastomer and also inside the elastomeric phase. Owing to the location of the clay particles, the average elastomer domain size in ternary nanocomposites are found to be greater than that in the relative binary blends of PS-(SEBS-g-MA). Moreover, with the organoclay addition, phase inversion point shifts to lower elastomer contents. The mechanical test results showed that the nanocomposites containing 15 and 20 wt% SEBS-g-MA have the optimum average domain size that results in high-impact strength values without deteriorating the tensile properties. POLYM. COMPOS., 31:1853–1861, 2010. © 2010 Society of Plastics Engineers.

Drop sizes and particle coverage in emulsions stabilised solely by silica nanoparticles of irregular shape

We have investigated emulsions stabilised solely by partially-hydrophobised fumed silica particles which consist of a mixture of primary particles and irregularly-shaped fused aggregates and larger agglomerates. The particle wettability is controlled by varying the extent of hydrophobisation of their surfaces. This, in turn, controls the contact angle between the oil-water interface and the particle surface (θ(ow)) which affects the particle adsorption energy and the type of emulsion formed (oil-in-water, o/w or water-in-oil, w/o). Progressive particle hydrophobisation causes transitional phase inversion of the emulsions from o/w to w/o which occurs when θ(ow) = 90° and the energy of particle adsorption to the oil-water interface is maximally favourable. The key problem addressed here is to understand why the emulsion drop size passes through a minimum at the point of emulsion phase inversion. In principle, this effect could be the result of particle desorption, changes in the extent of close-packing of the adsorbed particle film (at constant particle orientation), particle re-orientation or a combination of these processes. Using measurements of emulsion drop size and the extent of particle desorption, we have derived adsorbed particle surface concentrations as a function of the energy of desorption of the particles from the oil-water interface for a range of particle concentrations and different oil-water systems. The main conclusion is that the minimum in emulsion drop size through phase inversion is mainly caused by re-orientation of the particles from a high surface area orientation when the energy of desorption is high to a low surface area orientation when the energy of desorption is low. Some particle desorption occurs but this is a secondary effect.

Droplet size and viscosity of tackifier emulsions formed via phase inversion

AbstractTackifier dispersions used in pressure‐sensitive adhesives are made by phase inverting an aqueous rosin ester emulsion. The recipe also includes rosin acid and potassium hydroxide which react to form a surfactant. The amount of surfactant available plays a key role in determining dispersion properties. As the surfactant concentration increases, the point of phase inversion is delayed to larger dispersed phase concentrations. This also results in excess dispersant in the liquid phase and a narrower particle size distribution, even though the droplet size remains relatively unchanged.

Phase Inversion in Polylactide/Soybean Oil Blends Compatibilized by Poly(isoprene-b-lactide) Block Copolymers

Renewable composites were prepared by melt blending of polylactide and soybean oil. The blend morphology was tuned by the addition of poly(isoprene-b-lactide) block copolymers. Due to the extreme difference in the viscosities of soybean oil and polylactide, a critical block copolymer composition was found to induce a phase inversion point at which the minor soybean oil phase became the matrix surrounding polylactide particles. This transition was due to the thermodynamic interactions between the block copolymer and the two phases and shear forces acting on the mixture during blending. The size of the soybean oil droplets in the polylactide matrix was also highly dependent on the block copolymer composition. In binary polylactide/soybean oil blends, there was a limiting concentration of soybean oil that could be incorporated into the polylactide matrix (6% of the total blend weight), which could be increased up to 20% by the addition of block copolymers.

Evaluation of the Final Morphology of HIPS Based on the Architecture of the Compatibilizer Graft Copolymer PBd‐g‐PS

AbstractHigh Impact Polystyrene (HIPS) was synthesized by radical bulk polymerization at 70 °C using 6% w/w of total rubber and 0.01% w/w of azobisisobutyronitrile (AIBN) as radical initiator, where the total rubber was composed by polybutadiene (PBd) and model graft copolymers PBd‐g‐PS. Different ratios in weight percent of PBd to PBd‐g‐PS were used in order to evaluate the effect of the graft copolymers on the morphology development of the rubber particles during the HIPS synthesis reaction. The morphology of the final material was evaluated by Transmission Electron Microscopy (TEM). The model graft copolymers used with controlled architecture and molecular weight were synthesized previously by high vacuum anionic polymerization. Results show that increasing the content and changing the architecture of the graft copolymer significantly affects the phase inversion point.

A SIMPLE THEORETICAL MODEL FOR PREDICTION OF PHASE INVERSION

Phase inversion in liquid-liquid dispersions corresponds to the transitional boundary between Oil-in-Aqueous dispersion and Aqueous-in-Oil dispersion. A theoretical model based on simple assumptions was proposed to predict phase inversion point, ambivalence region and the hysteresis effect of inversion. Experimental data from the literature were used to validate the model and results were compared with those obtained by the Yeo et al. model. Comparison shows that there is a reasonable agreement between the suggested model and the experimental results taken from the literature. It is also pointed out that this model generates smaller relative errors than the previous work of Yeo et al. does.

Influence of a surfactant or salt on phase inversion in a water–oil pipe flow

Phase inversion experiments have been performed with a water–oil flow through a pipe to study the effect of the addition of a surfactant or of salt on the critical dispersed phase volume fraction (at the point of phase inversion). The addition of a surfactant caused a small change in the critical volume fraction, but the general form of the ambivalence region in the inversion map remained the same. The influence of salt was negligible.

Effect of drag reducing polymers on oil–water flow in a horizontal pipe

Measurements of drag-reduction are presented for oil–water flowing in a horizontal 0.0254 m pipe. Different oil–water configurations were observed. The injection of water soluble polymer solution (PDRA) in some cases produced drag reduction of about 65% with concentration of only 10–15 ppm. The results showed a significant reduction in pressure gradient due to PDRA especially at high mixture velocity which was accompanied by a clear change in the flow pattern. Phase inversion point in dispersed flow regime occurred at a water fraction range of (0.33–0.35) indicated by its pressure drop peak which was disappeared by injecting only 5 ppm (weight basis) of PDRA. Effect of PDRA concentration and molecular weight on flow patterns and pressure drops are presented in this study. Influence of salt content in the water phase on the performance of PDRA is also examined in this paper.

A methodology for predicting phase inversion during liquid–liquid dispersed pipeline flow

In this paper, a methodology is developed for predicting the phase inversion point in dispersed liquid–liquid flows. It is suggested that phase inversion happens at the phase fraction where the difference in viscosities between the two possible dispersions, oil continuous and water continuous, is zero, which enables the transition from one continuous phase to the other. A large number of literature correlations were used to calculate the mixture viscosity and the predicted phase volume fractions for inversion were compared against experimental data. From the various viscosity models, those by Brinkman [Brinkman, H.C., 1952, The viscosity of concentrated suspensions and solutions, J Chem Phys, 20(4): 571], Roscoe [Roscoe, R., 1952, The viscosity of suspensions of rigid spheres, Br J Appl Phys, 3: 267–269], Furuse [Furuse, H., 1972, Viscosity of concentrated solution, Jpn J Appl Phys, 11(10): 1537–1541] and Pal [Pal, R., 2001, Single-parameter and two-parameter rheological equations of state for nondilute emulsions, Ind Eng Chem Res, 40: 5666–5674] always predicted phase inversion within the experimental range. In addition, the phase inversion points predicted with the proposed methodology were very close to both the experimental finding and model by Yeh [Yeh, G.C., Haynie Jr., F.H., Moses, R.A., 1964, Phase volume relationship at the point of phase inversion in liquid dispersions, AIChE J, 10(2): 260–265].

EXPERIMENTAL INVESTIGATION OF PHASE INVERSION OF LIQUID-LIQUID SYSTEMS IN A SPRAY EXTRACTION COLUMN

An experimental study of the phase inversion behavior of liquid-liquid dispersion has been conducted in a spray extraction column for systems of toluene / water, n-hexane/water, CCl4/water, toluene /water + glycerol (25 % wt), toluene + CCl4 (25 % wt) / water and toluene / acetic acid (5 % wt)/water. The effects of physical properties, mass transfer and column geometry on phase inversion have been investigated. The results show that the dispersed phase hold up sufficient for phase inversion increases in o/w dispersion and decreases in w/o dispersion by increasing interfacial tension. Also, it was found that by increasing the viscosity of aqueous phase, dispersed phase hold up decreases at phase inversion point in both o/w and w/o dispersions. The tendency to phase inversion increases in o/w dispersion with an increase in density difference of two phases. It was observed that dispersed phase hold up at phase inversion point decreases in the presence of mass transfer, when the direction of mass transfer is from dispersed phase to continuous phase. The results show that dispersed phase holdup increases with drop size at phase inversion point and column diameter has an important effect on phase inversion because of wall effect.

Experimental investigation of three-phase flow in a vertical pipe: Local characteristics of the gas phase for gas-lift conditions

Laboratory experiments have been performed on the flow of oil, water and air through a vertical pipe in order to study the gas-lift technique for oil–water flows. Special attention was paid to the phase inversion phenomenon, by which the continuous phase switches to the dispersed phase and vice versa. By using different types of gas injectors the influence of the bubble size of the injected air on the efficiency of the gas-lift technique (in particular at the point of phase inversion) was studied. Also the gas and liquid mixture velocities were varied. The air bubbles were detected by means of optical fibre probes. Local measurements of the time-averaged gas volume fraction, bubble size and bubble velocity were carried out, as well as pressure measurements. Phase inversion is associated with a sharp increase of the pressure gradient. With air injection the pressure gradient (for the oil–water–air flow) is always significantly smaller than for the case of oil–water flow, except at the point of phase inversion where the pressure drop can be even be higher than for oil–water flow. It was also found that air injection does not significantly change the critical concentration of oil and water where phase inversion occurs. An important phenomenon to explain these results is, that the presence of the dispersed (oil or water) phase has a significant influence on the bubble size. Also the influence of the gas flow rate on the distribution of the oil and water phases in a cross-section of the pipe plays a significant role.

Morphology development in polyethylene/polystyrene blends: the influence of processing conditions and interfacial modification

AbstractThe influence of processing conditions and interfacial modification on the morphology evolution and the composition range within which fully co‐continuous high density polyethylene/polystyrene blend structures can exist during blending in a single screw extruder was studied. Blends ranging from pure A to pure B component, with and without compatibilizer, were prepared under two different shear rates. It was found that high shear rates displaced the breakdown–coalescence balance of the dispersed nodules to the side of coalescence, narrowing the percolation domain and the critical composition for full co‐continuity decreased with increasing shear rates. The addition of a tri‐block compatibilizer induced the percolation threshold of the polystyrene phase to begin at lower percentages of polyethylene but the phase inversion point did not change. The experimental results are discussed in the light of various theoretical models. Copyright © 2005 Society of Chemical Industry

Investigation of phase behavior during melt processing of novel inorganic‐organic polymer hybrid material

AbstractThe phase behavior of novel, binary organic‐inorganic hybrids consisting of an ultra‐low Tg tin‐based phosphate glass (Pglass) and polystyrene (PS) was investigated. Dynamic mechanical analysis (DMA) revealed that the glass transition peaks of the PS changed slightly with Pglass volume fraction, leading to a broad peak at the phase inversion point. The phase inversion and degree of phase continuity of the hybrid were studied through solvent extraction, optical/scanning electron microscopy, and dynamic rheology. The Jordhamo and Utracki viscosity ratio models provided reliable estimates of the inversion point. Torque rheometry revealed a trend toward linear additivity within the temperature range 200°C–230°C. Small‐angle neutron scattering experiments gave further evidence of the hybrid phase incompatibility. The results of this study point to a promising new class of blend materials with the potential to present a unique combination of properties impossible to achieve with classical polymer blends. Polym. Eng. Sci. 44:1692–1701, 2004. © 2004 Society of Plastics Engineers.

Catastrophic phase inversion in region II of an ionomeric polymer-water system.

Previous work has identified distinct regions, on a phase inversion map, for dispersions of polyurethane ionomer (PUI) and water. In this study, events that occur, before, during, and after catastrophic phase inversion (provoked by adding water to polyurethane ionomer (PUI) in the RII regions of the phase inversion map) have been studied in order to characterise the inversion mechanism. Before phase inversion, initial water addition leads to the hydration of ionic groups and eventually water drops start to form in the hydrophobic portions of the polymer matrix. At the phase inversion point, the PUI-water interface restructures and the ionomer disintegrates into a dispersion of spherical particles enclosed by a continuous aqueous phase. It is suggested that pseudo-drop structures are formed simultaneously during the production of the small polymer-in-water drops. After phase inversion, water addition dilutes the emulsion and destroys the apparent ionic-centre-rich environment surrounding any isolated ionic groups on a particle surface. The larger water-in-polymer drops are likely to have participated in the phase inversion and the smaller water drops form the primary water drops in the multiple emulsions. The resultant emulsions are stable over a period of a few months but very few multiple drops remain after 1(1/4) years.