Emulsions inversion

N. Monfreux, P. Perrin, F. Lafuma, and C. Sawdon. Invertible emulsions stabilised by amphiphilic polymers and application to bore fluids (emulsions inversables stabilisees par des polymeres amphiphiles et application a des fluides de forage). Patent WO 0031154, 2000. 

Mechanical agitation of the cream - a process called whipping - creates a metastable foam (i.e. it contains much air). Further whipping causes this foam to collapse some water separates out, and the major product is yellow butter. Incidentally, butter is a different form of colloid from milk, since its dispersed medium is water droplets and its dispersal phase is oil (milk is an oil-in-water colloid). Forming butter from milk is a simple example of emulsion inversion. 

J.L. Salager Phase Transformation and Emulsion Inversion on the Basis of Catastrophe Theory. In P. Becher (ed). Encyclopedia of Emulsion Technology. Vol. 3. Basic Theory. Measurement. Applications. Marcel Dekker, New York (1988). 

J.L. Salager A 3rd Type of Emulsion Inversion Attained by Overlapping the Two Classical Methods Combined Inversion. In Proceedings of the 3rd Word Congress on Emulsions l-E-180, Lyon, Erance (2001). 

J.L. Salager, M. Minana-Perez, M. Perez-Sanchez, M. Ramirez-Gouveia, and C.I. Rojas Surfactant-Oil-Water Systems near the Affinity Inversion. Part HI The Two Kinds of Emulsion Inversion. J. Dispersion Sci. Technol. 4, 313 (1983). 

J. Allouche, E. Tyrode, V. Sadtler, L. Choplin, and J.L. Salager Simultaneous Conductivity and Viscosity Measurements as a Technique to Track Emulsion Inversion by the Phase-Inversion-Temperature Method. Langmuir 20, 2134 (2004). 

Salager JL, Minana-Perez M, Perez-Sanchez M, Ramirez-Gouveia M, Rojas Cl (1983) Surfactant-oil-water systems near the affinity inversion. Part III The two kinds of emulsion inversion. J Dispers Sci Technol 4 313... 

Figure 6.22 Illustration of the influence of phase volume fraction on the emulsion type and viscosity of a hypothetical emulsion. In this example emulsion inversion from O/W to W/O occurs over a narrow range of oil volume fractions, centered at 4> = 0.74.

A device designed to permit observation of the conditions under which emulsion inversion occurs. 

Salager, J.L., Forgiarini, A., Marquez, L., Pena, A., Pizzino, A., Rodriguez, M.P., and Rondon-Gonzalez, M. (2004). Using emulsion inversion in industrial proeesses. Adv. Coll Interf Sci. 108-109,259-272. 

Monitoring Emulsion Aging. The surfactants used in transport emulsions may gradually lose their ability to stabilize the oil droplets. As the oil droplets coalesce, a two-phase mixture is formed, and it remains pumpable with no significant change in effective viscosity. This process is referred to as emulsion failure. An alternative to this process is inversion of the emulsion, in which a water-in-oil emulsion is formed with a potentially very high viscosity. Proper selection of the surfactant formulation can prevent the occurrence of emulsion inversion. 

Lim, K.-H. and Smith, D.H. (1991) Experimental test of catastrophe theory in polar coordinates Emulsion inversion forthe ethanol/benzene/water system. /. Colloid Interface Sci., 142,278-290. 

Salager JL. Phase transformation and emulsion inversion on the basis of catastrophe theory. In Ref. 4 79-134. 

Colloidal additives are interfacial active substances which can destroy emulsions or weaken the protective film and can transform the native water in oil emulsion into the opposite type (oil in water) i.e. it can promote emulsion inversion. 

Other emulsification protocols are based on a transient phenomenon, in which a dominant role is played by an unsteady mechanism, e.g., rrutss transfer through interface, which is not easy to ascertain or control. Often the nonequilib-riuin is driven by a continuously programmed change in a single variable such as temperature, amount or type of surfactant, watcr-to-oil ratio, etc., so that a phase behavior fionlicr is crossed and some event such as an emulsion inversion... 

In all experimental cases, the optimum formulation cun be detected by any of the phenomena that happen there, such as three-phase behavior, (b) single-phase behavior in-heiween two biphasic behaviors at high surfactant concentration, (cl inierfacial tension minimum, which is purticuiurly suitable when a very Mill 11 amount of surfactant is present so that no inicroemulsion is fonned, (d) change in preferred panitioning, and (e) several emulsion properties such as emulsion inversion and minimum stability that will be discussed in detail in the next chapter. 

Figure 8 indicates a typical variation of viscosity with internal phase content. It is seen that the increase in viscosity with the internal phase proportion starts slowly then turns faster and faster, until an almost vertical vwation is registered near the emulsion inversion value, here at about 82% of internal... 

Figure 20 Bidimensional formulation-compostlion map, showing the emulsion inversion locus, in case of strongly slanted optimum formulation band. (After Ref. 2.)...

Up to now the inversion line has been the limit between emulsion types when emulsihcalion is carried out from a preequiljbrated system according to the so-called standard procedure. In practice the emulsion inversion could also be the situation in which a change in formulation or composition triggers a switch in emulsion type. This kind of inversion is generally called dynamic inversion since it takes place as a consequence of the change. Depending on the circumstances it may be favorable or quite detrimental, and should be either harnessed or avoided. 

Figure 22 Dynamic changes that produce the emulsion inversion. (After Ref. I(X).)...

Intensive work has been carried out in order to estab lish a relationship between emulsion properties and the properties of surfactant systems. The classical HLB (hydrophile-lipophile balance) concept is widely used in emulsion science to describe the balance of the hydrophilic and lipophilic properties of a surfae tant at oil/water interfaees. The HLB value deter mines flie emulsion inversion point (EIP) at which an emulsion ehanges from W/O to 0/W type. This was of particular importance for nonionic surfactants that change their properties with ehanges in tempera ture (59). Various NMR techniques have provided significant contributions to this basic understanding of surfactant systems and some of those were reviewed in Ref. 7. The usefulness of NMR techni ques in studying surfactant solutions lies in the direct information they provide about the microstracture ofmicroheterogeneous systems (8,60— 64). It is beyond the scope of this chapter to summarize the use of NMR techniques in the study of surfactant systems, but we will present some representative examples related to emulsions. 

Emulsions can be found as two basic types, i.e., 0/W and W/O, but in some particular cases, multiple or double emulsions labeled Wj/0/W2 and Oj/W/02 also occur. The emulsion type may be determined by different methods. In most applications the aqueous phase contains one or various electrolytes, and thus conducts electricity somehow, whereas the oil or organic phase does not. Consequently, the measurement of electrolytic conductivity is a handy way to ascertain the emulsion type. Moreover, the continuous monitoring of the electrolytic conductivity allows the determination of the change in emulsion type which is referred to as emulsion inversion. 

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