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Ind. Eng. Chem. Res. 2008, 47, 2314-2319
Emulsion Catastrophic Inversion from Abnormal to Normal Morphology. 7. Emulsion Evolution Produced by Continuous Stirring To Generate a Very High Internal Phase Ratio Emulsion Marianna Rondo´ n-Gonza´ lez,†,‡ Ve´ ronique Sadtler,† Philippe Marchal,† Lionel Choplin,† and Jean-Louis Salager*,‡ Centre de Ge´ nie Chimique des Milieux Rhe´ ologiquement Complexes (GEMICO), ENSIC, Institut National Polytechnique de Lorraine, Nancy, France, and Laboratorio FIRP, Ingenierı´a Quı´mica, UniVersidad de Los Andes, Me´ rida, Venezuela
When emulsion inversion is produced by continuous stirring, from an abnormal water-in-oil-in-water (w/O/ W) system to a normal water-in-oil (W/O) morphology, to create a very high internal phase ratio emulsion (water fraction fw >0.85), the main mechanism is the continuous inclusion of the initial W external phase as w droplets into the dispersed O drops, which results in an increase of the dispersed (w + O) volume. Once a critical dispersed volume fraction is reached and a local inversion is detected, an additional stirring time, referred as “propagation time”, is required in order to complete the inversion of the system into a W/O morphology, instead of the usual behavior which is an almost instant culmination. This time is related to the energy input necessary to overcome the Laplace pressure involved in the change of the interfacial curvature. The present work shows how this propagation time is affected by the formulation, the composition, and the stirring conditions. Introduction Very high internal phase content emulsions are widely found in foods, cosmetics, pharmaceuticals, paints, and other applications, and are also used as a novel reaction medium because of their large interfacial area.1 The volume fraction of the dispersed phase of these emulsions exceeds Ostwald’s critical volume fraction for the sphere compact packing (0.74). Consequently, their structure consists of close-packed drops, often quite distorted from the spherical shape and separated by thin films of continuous phase. Because of their constitution and their viscosity, they are also called concentrated emulsions, high internal phase ratio (HIPR) emulsions, gel emulsions, or biliquid foams.2 They could contain up to 99% internal phase and generally exhibit viscoelastic properties. Usually, such emulsions are prepared by the slow addition of the internal phase in the external one, under continuous stirring, without inversion. However, they may also be prepared by mixing all components and submitting the system to a continuous stirring until phase inversion takes place.3,4 This mechanism offers some advantages over the conventional emulsification protocol: it is a one-step process and, by choosing the proper conditions, finer emulsions may be prepared at a low-energy expense and with a low surfactant concentration, even with viscous fluids. Phase inversion is a process in which an emulsion changes its morphology from oil-in-water (O/W) to water-in-oil (W/O) or vice versa, by one of two different paths corresponding to so-called transitional and catastrophic inversions,5 identified in the formulation-water/oil ratio bidimensional map6 and discussed in previous papers of this series.7,8 Generally, catastrophic inversion is produced by the addition of the internal phase, i.e., by increasing the dispersed phase * To whom correspondence should be addressed. E-mail : salager@ ula.ve. † Institut National Polytechnique de Lorraine. ‡ Universidad de Los Andes.
volume until a critical value is attained at which the dispersed phase drops are close enough to coalesce upon contact. However, it can also be induced by the continuous stirring protocol,7 which consists in submitting an abnormal system, prepared in the B- or C+ region of the formulation-composition map, to a mechanical stirring until the swap from a water-inoil to an oil-in-water emulsion (or vice versa) takes place. In this protocol, inversion takes place through the formation of a multiple morphology, in which the dispersed drops contain smaller inner droplets of the external phase. The multiple emulsion evolves with the transfer of more external phase as droplets inside the dispersed phase drops; this inclusion increases the dispersed phase volume, whose drops finally touch one another at some critical value, at which the coalescence happens and the inversion is completed.7-9 The influence on the emulsion produced by continuous stirring, of the surfactant concentration, the viscosities of internal and external phases, and the water fraction (fw) has been already reported in previous papers, for final emulsions containing up to 80% internal phase.8,9 The aim of the present work is to extend this inversion protocol by continuous stirring to prepare W/O emulsions containing a very high internal phase fraction (fw > 0.85), which have not been studied extensively, in spite of their interest.3,10 It will be shown next that in such extreme cases a peculiar progression is exhibited; i.e., the inversion propagates slowly through the system, according to an evolution which depends on the formulation, composition, and stirring conditions. Experimental Procedures Materials. Two polyethoxylated nonylphenol commercial surfactants (from Igepal CO series supplied by Sigma-Aldrich) in a total concentration of 2 wt % are used. Igepal CO-210, which contains an average of two ethylene oxide groups per molecule (noted in what follows as NP2EO, critical micelle concentration (cmc) around 0.005 wt %), is dissolved in the oil phase, while Igepal CO-630 (noted as NP9EO, cmc around
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0.002 wt %) is added to the water phase. A kerosene cut (with equivalent alkane carbon number EACN ) 10) and a 1 wt % NaCl brine are used as the oil and water phases. 2-Butanol is used as a cosurfactant, in a concentration that is varied from 0 to 6 wt %. This alcohol was chosen because it has essentially no effect on the formulation of the system, as its contribution in the hydrophilic-lipophilic deviation (HLD) equation is close to negligible.11 Furthermore, it has roughly the same affinity for the oil and water phases, and strongly coadsorbs in the interfacial layer.12 For the surfactant concentration study, a system containing Span 80 (sorbitan monooleate from Aldrich) as lipophilic surfactant and Igepal CO-630 as hydrophilic surfactant, was used in a concentration ranging from 2 to 7 wt %. Continuous Stirring Protocol. All inversion experiments are carried out from an abnormal (unstable) w/O/W or O/W emulsion to a normal (stable) W/O one, in the C+ f A+ direction in the bidimensional formulation-composition map.6-8 Abnormal systems with a total volume of 70 mL, containing a high initial water phase fraction (fw) ranging from 0.70 to 0.95 and a variable but hydrophobic formulation (as HLD > 0), are preemulsified during 40 s using an Ultra-Turrax turbine blender (IKA T25 Basic with Dispersion Tool S25-NK-19G, Germany) rotating at 8000 rpm. They are next poured into a “rheomixer” device, which, as described in previous papers,7,8,10 allows following the effective viscosity of the system. Then, these w/O/W abnormal emulsions are submitted to continuous stirring until the phase inversion to a W/O type is detected by simultaneous changes in both conductivity and viscosity. In the present case the experiment is not stopped at the first indication of a reduced conductivity, but up to the point where the conductivity becomes essentially zero and stable, with the viscosity high and stable. Three different impellers (an U-type anchor, a helix ribbon, and a three-stage dual-bladed paddle) were used. The effective shear rate of the vessel was varied from 80 to 4000 s-1 and the rotational speed of the Ultra-Turrax (DI 25 basic with dispersion tool S25N-10G, from IKA Germany) from 0 to 13 000 rpm. The temperature of the system is controlled at 25 °C. The system conductivity is followed up by using a CDM 210 conductimeter from Radiometer Analytical (France) fitted with a bipolar conductivity cell CDC 749. The repeatability of the experiment was estimated at (10% by replicating three times the inversion of the system at HLD ) 1.84 and fw ) 0.9. Microscopic Observations. In order to interpret and to relate the change in conductivity with the emulsion morphology, systems were stabilized inside the rheometer at different conductivity values. For each conductivity value a stabilityenhanced system was prepared by adding 3.5 mL of a concentrated solution (20 wt %) of polymeric surfactant Synperonic PE/F68 (from Fluka). This results in a 1 wt % polymer concentration whose corresponding viscosity “quenches” the morphology for some time. After 1 min of low mixing with the anchor impeller, whose shear cannot modify the emulsion drop size, a sample was withdrawn and a picture was taken with an Olympus BX51 microscope fitted with a A100 objective. Formulation Scans. All inversion experiments are performed from an abnormal (unstable) w/O/W or O/W morphology to a normal (stable W/O) one. The formulation variable used in all cases but the surfactant concentration study is the hydrophiliclipophilic deviation (HLD), which includes the contributions of all variables.13
Table 1. Composition of Systems under Study: Total Surfactant Concentration 2 wt %
case
HLD
NP2EO (wt % in the surfactant mixture)
mechanism HLD study
1.84 1.16 1.39 1.60 1.84 2.01 2.20 1.84 1.84 1.84 1.84
72.5 60.0 64.0 68.0 72.5 76.0 80.0 70.5 72.5 74.5 72.5
alcohol study stirring conditions
NP9EO (wt % in the surfactant mixture)
2-butanol (wt %)
27.5 40.0 36.0 32.0 27.5 24.0 20.0 29.5 27.5 25.5 27.5
2 2 2 2 2 2 2 0 2 4 2
Numerically, it is given by
HLD ) R - EON + bS - k(ACN) + t(T - 25) + aA where R, k, and t are parameters depending on the surfactant type. EON is the average degree of ethoxylation of the surfactant; ACN is the oil alkane carbon number or its equivalent EACN if the oil is not a n-alkane, S and A are the salt and alcohol concentrations (weight percent), b and a are the constants characteristic of each type of salt and alcohol, and T is the temperature.11,14 Table 1 gathers the characteristics of the systems used in the different experimental runs and indicates the proportion of the two surfactants used in each case. In the case of the alcohol study, this proportion has been adjusted to keep a constant formulation at HLD ) 1.84. The HLD value of experiments is determined by using the following values: R ) +6.5, b ) 0.13, k ) 0.15, t ) 0.06, a ) 0.05, and EACN ) 10 (experimentally determined).12,14 Results Figure 1 shows the conductivity and viscosity variations during a catastrophic inversion produced by the continuous stirring of an abnormal system containing a water fraction fw ) 0.7, i.e., a high but not very high water content. The figure reveals the progression described in a previous paper:7 As time elapses under constant stirring, the emulsion conductivity decreases slowly. This is a clear indication of the continuous reduction of the volume of the external (W) phase through its
Figure 1. Conductivity and viscosity variations with time in a typical inversion experiment of a system prepared at fw ) 0.70 with 2 wt % total surfactant concentration and HLD ) 1.84 (NP2EO ) 73 wt % and NP9EO ) 67 wt %).
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Figure 2. Conductivity and viscosity variations with time in a typical inversion experiment of a system at fw ) 0.90 with 2 wt % total surfactant concentration and HLD ) 1.84 (NP2EO ) 73 wt % and NP9EO ) 67 wt %).
inclusion as inner (w) water droplets inside the (O) oil phase drops. This inclusion mechanism is corroborated by the concomitant increase in emulsion viscosity. Consequently, as the stirring continues, the volume of the dispersed phase, which contains the oil drops with included water droplets, increases until a critical value is reached and the inversion is triggered. It was shown in a previous paper7 that when such inversion is produced in systems containing an intermediate to moderately high water fraction (0.6 < fw < 0.8), the complete inversion of the emulsion, from w/O/W to W/O, takes place rapidly, almost instantaneously. As shown in Figure 1, both the conductivity and viscosity exhibit a very quick change once the critical dispersed fraction is reached after about 6000 s. The inverted emulsion is a simple W/O morphology as indicated by a constant viscosity and confirmed by microscopic observations beyond 6300 s. Nevertheless, it is found that at a very high water fraction (e.g., fw ) 0.9), the inversion does not take place in the same way, as seen from the change in properties with time exhibited in Figure 2. Before the inversion, the conductivity decreases and the viscosity increases as in the previous case, but at the onset of inversion, which is detected by the essentially zero conductivity at 1200 s, the system does not switch rapidly to a W/O morphology as in the Figure 1 case. Actually, two different morphologies seem to coexist: a recently gathered oil continuous zone that contains the inverted W/O emulsion, and on the other hand the remains of the initial multiple w/O/W emulsion. Figure 2 indicates that a change in viscosity is also exhibited at 1200 s, but it is much less significant than in the previous case, most likely because only a part of the system is inverted into a W/O emulsion. Visual observation confirms that, after 1200 s, there is still a multiple morphology from place to place when the emulsion conductivity becomes close to zero with some erratic peaks from time to time. To complete the inversion process, particularly to attain a high and constant viscosity and to observe only a W/O simple morphology, some more time, referred to as “inversion propagation time”, is required. In
Figure 3. Progression of emulsion morphology in Figure 2 case.
essence this inversion propagation time is the period through which the normal morphology propagates through the system, presumably as a result of the fading away of the remnants of the initial multiple morphology. It is seen in Figure 2 that this propagation time is essentially as long as the time for the onset of inversion, which means that it is quite significant in practice. Figure 2 indicates that the increase in viscosity during this evolution period takes place with quite erratic variations, also associated with conductivity spikes, until the complete inversion to a W/O morphology finally happens at 2600 s, beyond which the conductivity and viscosity become steady. The existence of this propagation time may be explained by the combination of several phenomena that take place simultaneously during the inversion process from w/O/W to W/O morphologies. Due to the formulation conditions (HLD > 0), the O/W outer emulsion is unstable and the oil phase (O) drops coalesce to make the new external phase. In this process, the inner w droplets (which are included in O drops) become the first type (W1) of drops of the inverted W/O emulsion, as indicated in Figure 3. At the same time, the water films that form the external phase W of initial w/O/W emulsion, break and form the second type (W2) of drops that disperse in the O new external phase. It is worth remarking that these W2 drops are not produced by the same mechanism as W1 drops; hence they may eventually exhibit a completely different size. In Figure 3, both kinds of W drops are indicated with different shades, although they obviously come from the same water phase. On the other hand, since the system is homogenized, both types of W drops are randomly dispersed in the O new external phase, without coalescing because of the stabilizing (HLD > 0) formulation condition. In order to complete the emulsion inversion from O/W to W/O, the Laplace pressure differential due to curvature has to be overcome. For spherical drops, Laplace pressure differential is given by ∆P ) 2γ/R, where γ is the interfacial tension and R is the drop radius. When the formulation is close to optimum, the interfacial tension is low and the Laplace pressure differential is weak; thus inversion is able to take place with a minimum energy input (as for the transitional inversion). However, with the higher interfacial tension prevailing in systems away from optimum formulation, it is the capillary or Weber number (We), i.e., the ratio of the deforming stress to the restoring Laplace stress, which determines the drop distortion and the probability of reaching the almost zero curvature required to impose the inversion. In the following definition of We:
We )
2ηcγ˘ R γ
ηc is the continuous phase viscosity and γ˘ is the local shear rate. If We is high enough, for instance if the tension γ is low, or if enough energy is provided to the system to force a close-tozero curvature, the new drops (W2) are readily formed from the films and inversion would take place rapidly as in the Figure
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Figure 4. Microscope pictures illustrating the morphology change during the inversion experiment at fw ) 0.9 (Figure 2 conditions). φ represents the (O + w) dispersed phase proportion of the system at the moment it is stabilized.
1 case. If not, additional stirring time (defined here as the “propagation time”) is required to complete the inversion to a W/O morphology. As will be seen next, this time could vary from minutes to hours, depending on formulation, composition, and process variables. Because of the instability of the system before the inversion (since it is an abnormal emulsion), the direct observation of its morphology is a delicate issue. However, the relative change in the morphology with stirring could be observed if the system stability is enhanced by adding a polymer which slows down any evolution and allows taking a sample and observing it with a microscope. Figure 4 shows the aspect of systems stabilized at different times in the Figure 2 experiment. Each picture corresponds to a different value of dispersed phase fraction φ, which is the (O + w) actual internal phase proportion of the emulsion calculated from the conductivity using Bruggeman’s law. Pictures taken before the triggering of the inversion (A, B, C) confirm the formation of a multiple emulsion and the continuous increases of the dispersed phase fraction with stirring time. During propagation time, i.e., in the 1250-2500 s range, pictures of two different systems confirm the existence of a w/O/W (diluted) morphology (D) and an inverted W/O emulsion (E). Finally, at 2700 s, i.e., after the inversion is completed, a W/O very concentrated emulsion (90% water) is exhibited with a droplet size less than 1 µm (F). The resemblance of the morphology of the emulsion after complete inversion (F) to that during propagation (E) validates the hypothesis that an inverted system coexists with the multiple system during propagation. Effect of Formulation on Inversion Propagation Time. The role of the formulation in the evolution of the inversion is crucial, as shown in Figure 5. As HLD decreases, i.e., when optimum formulation is approached, the propagation time required to finish up the inversion of the system quickly diminishes and becomes essentially zero for HLD e 1. This is probably due to the accumulation of two effects that occur close to optimum formulation, i.e., the strong reduction in interfacial tension and hence an increase in We, and the higher coalescence rate of the O drops.15 Moreover, the stirring becomes more efficient as the interfacial tension decreases, and new W2 drops may be quickly formed from the easy elongation of the W external phase films.
Figure 5. Effect of general formulation HLD on the inversion propagation time. Systems with 2% total surfactant (variable mixture of NP2EO and NP9 EO) at fw ) 0.9.
As a consequence, the inversion takes place readily, with an essentially zero propagation time. The increase of the inversion propagation time with formulation is considerable when HLD increases beyond 1.8. For systems prepared at HLD higher than 2.2 (not shown in Figure 5), the complete inversion of the system is actually never reached. At an HLD about 2.6, the viscosity of the system after inversion does not change anymore, which is a strong clue that inversion does not propagate. When HLD g 3, the conductivity of the system remains constant after some stirring time, and the inversion is never triggered, indicating that an equilibrium between the inclusion and escape phenomena is reached. The same strong increase in propagation time when HLD departs from optimum has been observed too at a higher water fraction fw ) 0.95. When HLD ) 0.66, the propagation time is 6000 s, while at HLD ) 1.16 the propagation is never completed. These results suggest that the effect of the HLD on the propagation time is directly linked with its influence on the antagonistic (inclusion and escape) mechanisms. The main issue is probably the strong change of the interfacial tension with the HLD around optimum formulation. However, the effect is likely to be boosted by the surfactant partitioning between phases, particularly the low ethoxylation oligomers (EON < 3) which tend to migrate into the oil phase.16 The HLD increase is attained by raising the proportion of NP2EO in the surfactant mixture. Since most of the oligomers of this low ethoxylation surfactant tend to migrate into the oil, the concentration of surfactant at the interface decreases. This effect tends to raise the interfacial tension and to reduce the stability of the normal morphology emulsion, thus favoring the
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Figure 6. Combined effects of formulation (effective HLD) and composition (fw) on inversion propagation time. Figure shows isopropagation time lines: squares indicate propagation time ) 0 and circles indicate propagation time ) 3000 s. A 2 wt % total surfactant concentration (variable mixture of NP2EO and NP9EO).
escape of inner water droplets in the w/O/W system and increasing the propagation time. In Figure 5, it is worth remarking that an HLD ) 1 situation is favorable to quickly attain a W/O high internal phase ratio morphology, but that the proximity of optimum formulation might not ensure a long-term stability of the resulting emulsion. Consequently, an HLD ) 2 formulation is likely to be a better compromise in practice to quickly manufacture a stable W/O gel emulsion. Effect of Water Fraction on Inversion Propagation Time. The inversion propagation time was also found to depend on the water fraction of the system. At HLD ) 2.2, the evolution time is 0 at fw ) 0.8, 200 s at fw ) 0.85, and 13 800 s at fw ) 0.9. Since a higher water content would require a larger volume of W to be transferred as w droplets in O drops (to later become W1 droplets), the expected trend is a longer propagation time, particularly when the formulation is away from optimum. This increase of the inversion propagation time is associated with the catastrophic character of the process already related to the poor reproducibility mentioned in a previous paper7 and corroborated by the erratic variations in Figure 2. Moreover, the existence of a noninstantaneous propagation of the inversion after its onset appears to be due to the combined effects of formulation (HLD) and composition (fw). This coupling is shown in Figure 6, with the shaded region indicating the zone with a noninstantaneous inversion propagation. Nevertheless, and since the interfacial composition of surfactant mixtures change with the water/oil ratio, this coupling may be due (at least in part) to the change in fractionation of the surfactant species with fw. In order to eliminate this effect, the formulation is represented in Figure 6 as the effective HLD, calculated as the difference between the HLD of the mixture and the optimal HLD exhibited at the same water/oil ratio.16,17 Hence, the separate influence of the composition (fw) on the propagation time (and not the effect of formulation), is unambiguously exhibited in Figure 6. Let us define an emulsion located in the center of the A+ zone of the formulation-composition map as a “most normal” W/O emulsion (with intermediate fw and at HLD > 0 far from optimum formulation) because it is associated with the most stable case;6 conversely let us define a “most abnormal” emulsion as the one corresponding to the maximum conflict between formulation and composition, i.e., an O/W morphology with high fw and far from zero positive HLD in the upper right part of the C+ region. Then, it may be said that the “more abnormal” the original emulsion is, the slower is the inversion propagation, and vice versa. In such a view, the degree of “morphology abnormality”, which somehow represents the intensity of the conflict between formulation and composition effects, is directly related to the difficulty of completing the inversion expressed as a longer inversion propagation time.
Figure 7. Effect of surfactant and alcohol concentration on inversion propagation time. fw ) 0.9, HLD ) 1.84.
Figure 8. Effect of stirring conditions (anchor and Ultra-Turrax turbine) and toll (anchor, helix ribbon, paddles at 80 s-1) on inversion propagation time. fw ) 0.9, HLD ) 1.84.
Effect of Surfactant and Alcohol Concentrations on the Inversion Propagation Time. The inversion propagation time is reduced by a decrease of surfactant concentration and an increase of alcohol amount, as indicated in Figure 7. The most likely explanation is that, in both cases, the density of adsorbed surfactant at the interface is lowered, thus making the rupture of W films easier, hence speeding up the propagation. It is worth noting that the possible decrease of interfacial tension (and, thus, reduction of the propagation time) with an increase in surfactant concentration is probably not significant in the studied range, which is much beyond the critical micelle concentration. Effect of Stirring Conditions on Inversion Propagation Time. As shown in Figure 8a, the stirring conditions affect dramatically the inversion propagation time for systems prepared at the same formulation (HLD ) 1.84) and composition (fw ) 0.9) conditions. As the energy input increases, either through a higher shear rate of the anchor or by a quicker rotation of the Ultra-Turrax turbine (UT), the propagation time decreases. This may be readily interpreted through the variation of the Weber number away from optimum formulation, as discussed previously. The influence of the stirring tool is different. By changing the type of tool from an anchor to a three-stage dual-bladed paddle (Figure 8b), the evolution time decreases. This result is in agreement with a well-known trend in mixing technology.18 Helix ribbons (as other class III agitators) have better mixing performances for viscous fluids than anchors (and other class II agitators), which are known to produce poor axial circulation. It is then deduced that the better the mixing efficiency is, the lower is the stirring time required to complete the inversion.
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Conclusions When very highly concentrated W/O emulsions (fw > 0.85) are produced by the phase inversion of abnormal w/O/W emulsions induced by continuous stirring, the inversion does not take place instantaneously as with intermediate to moderately high internal phase emulsions (0.60 < fw < 0.80). After the critical dispersed phase fraction is reached at the onset of inversion, an heterogeneous system is formed with concomitant w/O/W and W/O morphologies and some additional stirring time, so-called inversion propagation time, is required to complete the morphology swap. This propagation time is found to directly depend on the Weber number, i.e., the ratio of the hydrodynamic force to the capillary force. Consequently, it depends on formulation, and is found to be essentially zero close to optimum formulation. Sensitivity tests also show that the propagation time depends on surfactant and alcohol concentrations, water fraction, and stirring conditions. The observed trends can be used in practice to select the proper conditions in order to minimize the required total stirring time and to facilitate the use of this inversion process to produce highly concentrated stable W/O emulsions with a minimum energy input. Acknowledgment The authors would like to thank the FUNDAYACUCHO Scholarship Program for helping financing M.R.-G.’s doctoral studies, and the Postgraduate Cooperation Program PCP (FONACIT-Venezuela and MAE-France) for sponsoring professor and graduate student exchanges. The authors wish to thank Mr. Jonathan Oates, who helped in some of the experiments. A partial financial backing from the University of the Andes Research Council CDCHT-ULA through Grant I-834-05-08AA is gratefully acknowledged. Literature Cited (1) Solans, C.; Esquena, J.; Azemar, N. Highly concentrated (gel) emulsions, versatile reaction media. Curr. Opin. Colloid Interface Sci. 2003, 8, 156-163. (2) Lissant, M. J. The geometry of high-internal-phase-ratio emulsions. J. Colloid Interface Sci. 1966, 22, 462-468. (3) Pons, R.; Carrera, I.; Erra, P.; Kunieda, H.; Solans, C. Novel preparation methods for highly concentrated water-in-oil emulsions. Colloids Surf., A 1994, 91, 259-266. (4) Tyrode, E.; Allouche, A.; Choplin, L.; Salager, J. L. Emulsion catastrophic inversion from abnormal to normal morphology. 4. Following the emulsion viscosity during three inversion protocols and extending the critical dispersed-phase concept. Ind. Eng. Chem. Res. 2005, 44, 67-74. (5) Salager, J. L. Phase Transformation and Emulsion Inversion on the Basis of Catastrophe Theory. In Encyclopedia of Emulsion Technology; Becher, P., Ed.; Marcel Dekker: New York, 1988; Vol. 3, Chapter 2.
(6) Salager, J. L.; Min˜ana-Perez, M.; Perez-Sanchez, M.; RamirezGouveia, M.; Rojas, C. I. Surfactant-Oil-Water System near the Affinity Inversion. Part III: Two Kinds of Emulsion Inversion. J. Dispersion Sci. Technol. 1983, 4, 313-329. (7) Rondo´n-Gonzale´z, M.; Sadtler, V.; Choplin, L.; Salager, J. L. Emulsion Catastrophic Inversion from Abnormal to Normal Morphology. 5. Effect of the Water-to-Oil Ratio and Surfactant Concentration on the Inversion Produced by Continuous Stirring. Ind. Eng. Chem. Res. 2006, 45, 3074-3080. (8) Rondo´n-Gonzale´z, M.; Madariaga, L. F.; Sadtler, V.; Choplin, L.; Salager, J. L. Emulsion Catastrophic Inversion from Abnormal to Normal Morphology. 6. Effect of the Phase Viscosity on the Inversion Produced by Continuous Stirring. Ind. Eng. Chem. Res. 2007, 46, 3595-3601. (9) Sajjadi, S.; Zerfa, M.; Brooks, B.W. Dynamic behavior of drops in oil/water/oil dispersions. Chem. Eng. Sci. 2002, 57, 663-675. (10) Rondo´n-Gonza´lez, M.; Sadtler, V.; Choplin, L.; Salager, J. L. Emulsion inversion from abnormal to normal morphology by continuous stirring without internal phase addition: Effect of surfactant mixture fractionation at extreme water-oil ratio. Colloids Surf., A 2006, 288, 151157. (11) Bourrel, M.; Salager, J. L.; Schechter, R. S.; Wade, W. H. A correlation for phase behavior of nonionic surfactants. J. Colloid Interface Sci. 1980, 75, 258-263. (12) Salager, J. L. Microemulsions. In Handbook of DetergentssPart A: Properties; Broze, G., Ed.; Marcel Dekker: New York, 1999; pp 253302. (13) Salager, J. L.; Ma´rquez, N.; Graciaa, A.; Lachaise, J. Partitioning of Ethoxylated Octylphenol Surfactants in Microemulsion-Oil-Water Systems. Influence of Temperature and Relation between Partitioning Coefficient and Physicochemical Formulation. Langmuir 2000, 16, 5534-5539. (14) Salager, J. L.; Anto´n, R. E.; Ande´rez, J. M.; Aubry, J. M. Formulation des micro-e´mulsions par la me´thode HLD. In Techniques de l’Inge´ nieur, Ge´ nie des Proce´ de´ s; Charpentier, J. C., Ed.; Techniques de l’Inge´nieur: Paris, 2001; Vol. J2, Paper J2-157. (15) Salager, J. L.; Loaiza-Maldonado, I.; Min˜ana-Perez, M.; Silva, F. Surfactant-oil-water systems near the affinity inversionsPart I: Relationship between equilibrium phase behavior and emulsion type and stability. J. Dispersion Sci. Technol. 1983, 3, 279-292. (16) Graciaa, A.; Lachaise, J.; Sayous, J. G.; Grenier, P.; Yiv, S.; Schechter, R. S.; Wade, W. H. The partitioning of complex surfactant mixtures between oil/water/microemulsion phases at high surfactant concentrations. J. Colloids Interface Sci. 1983, 93, 474-486. (17) Graciaa, A.; Ande´rez, J. M.; Bracho, C.; Lachaise, J.; Salager, J. L.; Tolosa, L.; Ysambertt, F. The Selective Partitioning of the Oligomers of Polyethoxylated Surfactant Mixtures between Interface and Oil and Water bulk Phases. AdV. Colloid Interface Sci. 2006, 123-126, 63-73. (18) Carreau, P. J.; De Kee, D. C. R.; Chabra, R. P. Liquid Mixing. In Rheology of polymeric systems. Principles and Applications; Hanser/Gardner Publications, Inc.: Cincinnati, 1997; pp 386-439.
ReceiVed for reView October 31, 2007 ReVised manuscript receiVed December 31, 2007 Accepted January 11, 2008 IE071482R
