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Dynamic inversion pattern-Hysteresis of the catastrophic inversion

Dynamic inversion pattern-Hysteresis of the catastrophic inversion

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Article
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Emulsions properties depend upon the combined effects of physico-chemical formulation, composition and stirring features used during the emulsification protocol. It is shown that according to the currently available know-how, the emulsification process characteristics can be set on a formulation-composition map and can be translated into process de...

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Context 1
... on dynamic inversion processes have shown that the horizontal branch of the inversion line is unchanged whatever the way it is crossed, whereas the vertical branches can be shifted by using a step-by-step emulsification protocol, e. g., by adding successive small amounts of internal phase to the emulsified system while keeping it under stirring. The location of the vertical branch of the inversion line depends on the direction of the composition change as indicated in figure 3 left graph, so that an hysteresis zone is exhibited (shaded in figure 3 right graph). This means that either a W/O or a O/W emulsion could be found in the shaded area depending upon the previous history of the emulsion [12][13]. ...
Context 2
... on dynamic inversion processes have shown that the horizontal branch of the inversion line is unchanged whatever the way it is crossed, whereas the vertical branches can be shifted by using a step-by-step emulsification protocol, e. g., by adding successive small amounts of internal phase to the emulsified system while keeping it under stirring. The location of the vertical branch of the inversion line depends on the direction of the composition change as indicated in figure 3 left graph, so that an hysteresis zone is exhibited (shaded in figure 3 right graph). This means that either a W/O or a O/W emulsion could be found in the shaded area depending upon the previous history of the emulsion [12][13]. ...
Context 3
... results in a memory effect that is quite useful in emulsion making. fig 3 right graph), and adding oil little by little (moving left). Doing so, the inversion line could be driven to the left up to 95% or more oil [6]. ...
Context 4
... the other hand, the emulsion type and other properties change when the inversion line is crossed. The transitional inversion (vertical crossing of the horizontal branch) allows the formation of so-called miniemulsions by the desorption of liquid droplets from a microemulsion (vertical arrows in figure 3 right graph) [14][15]. Similarly, the catastrophic inversion (horizontal crossing of a vertical branch) could lead under certain circumstances, to the formation of miniemulsions with a drop size that is unreachable by mechanical stirring disruption. ...

Citations

... This is essentially due to the fact that engineers involved in mixing-stirring technology do not know or do not care about physico-chemical formulation, whereas chemists or physical-chemists are not often concerned by hydrodynamics and mixing issues. As a consequence none of the current approaches is satisfactory for the emulsion maker, and all are likely to hinder the effects of coupled and competitive phenomena, although these have been recently reported to be determinant in many instances34. ...
... It is now well established that as formulation is changed from hydrophilic (HLD < 0) to lipophilic (HLD > 0) conditions, whatever the variable used to produce the change in HLD, the emulsion inverts from oil-in-water (O/W) to water-in-oil (W/O) a change which is known as Bancrofft's rule3536 because it essentially corresponds to what was enounced almost one century ago. It is now well accepted that the emulsion properties change according toFigure 1 scheme that sum up scores of experimental data34567891011. The emulsion drop size is the result of a dynamic equilibrium between two opposite effects: on the one hand those which tend to decrease the drop size, e. g., shearing or stirring, and on the other hand those which favor the coalescence between drops [2, 37]. ...
Article
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The emulsification yield, i. e., the reduction of drop size when a surfactant-oil-water system is stirred, can be altered by changing: 1) the physicochemical formulation variables which are linked to the nature of the water, oil, and emulsifier, 2) the composition variables (surfactant concentration and water- to-oil ratio) and 3) the variables which characterize the mechanical energy supplied by the stirring device. After reporting the general trends found in previous research, the best compromise situations to attain a minimum drop size are located in a three dimensional formulation-composition-stirring space.
... This is essentially due to the fact that engineers involved in mixing-stirring technology do not know or do not care about physico-chemical formulation, whereas chemists or physical-chemists are not often concerned by hydrodynamics and mixing issues. As a consequence none of the current approaches is satisfactory for the emulsion maker, and all are likely to hinder the effects of coupled and competitive phenomena, although these have been recently reported to be determinant in many instances [3][4]. ...
... It is now well established that as formulation is changed from hydrophilic (HLD < 0) to lipophilic (HLD > 0) conditions, whatever the variable used to produce the change in HLD, the emulsion inverts from oil-in-water (O/W) to water-in-oil (W/O) a change which is known as Bancrofft's rule [35][36]because it essentially corresponds to what was enounced almost one century ago. It is now well accepted that the emulsion properties change according to Figure 1scheme that sum up scores of experimental data [3][4][5][6][7][8][9][10][11]. The emulsion drop size is the result of a dynamic equilibrium between two opposite effects: on the one hand those which tend to decrease the drop size, e. g., shearing or stirring, and on the other hand those which favor the coalescence between drops [2, 37]. ...
Article
Full-text available
The effects of surfactant molecules involved in macro-, mini-, nano-, and microemulsions used in cosmetics and pharmaceuticals are related to their amphiphilic interactions with oil and water phases. Basic ideas on their behavior when they are put together in a system have resulted in the energy balance concept labeled the hydrophilic-lipophilic deviation (HLD) from optimum formulation. This semiempirical equation integrates in a simple linear relationship the effects of six to eight variables including surfactant head and tail, sometimes a cosurfactant, oil-phase nature, aqueous-phase salinity, temperature, and pressure. This is undoubtedly much more efficient than the hydrophilic-lipophilic balance (HLB) which has been used since 1950. The new HLD is quite important because it allows researchers to model and somehow predict the phase behavior, the interfacial tension between oil and water phases, their solubilization in single-phase microemulsion, as well as the corresponding properties for various kinds of macroemulsions. However, the HLD correlation, which has been developed and used in petroleum applications, is sometimes difficult to apply accurately in real cases involving ionic–nonionic surfactant mixtures and natural polar oils, as it is the case in cosmetics and pharmaceuticals. This review shows the confusion resulting from the multiple definitions of HLD and of the surfactant parameter, and proposes a “normalized” Hydrophilic-Lipophilic Deviation (HLDN) equation with a surfactant contribution parameter (SCP), to handle more exactly the effects of formulation variables on the phase behavior and the micro/macroemulsion properties.
Article
The authors have evaluated the emulsification of oil of varying viscosities for concentrated o/w emulsions (>60%). Rushton type impellers and baffled mixing vessels were used. The emulsions were prepared in the transition regime (80 < Re < 200). It was found that, when the oil content increases, it is the emulsion viscosity that controls droplet size, regardless of the dispersed phase viscosity and hydrodynamics. The authors have followed an experimental procedure that allows for the scale-up of the results.
Article
Full-text available
The reduction of drop size during emulsification may be favored by changing three types of variables: (1) the physicochemical formulation variables which are linked to the nature of the compounds (water, oil, emulsifier), (2) the composition variables that account for their relative proportions and (3) the variables which characterize the mechanical energy input conditions supplied by the stirring device. After reporting the general trends, the best compromise situations to attain a minimum drop size are located in the three dimensional formulation-composition-stirring space.