Winsor I microemulsion

Shioi A and Flarada M 1996 Model for the geometry of surfactant assemblies in the oil-rich phase of Winsor I microemulsions J. Chem. Eng. Japan 29 95... 

FIGURE 2.23 Fractional flow diagram of a Winsor I microemulsion flood. 

FIGURE 2.24 Saturation profile for a Winsor I microemulsion flood started at interstitial water saturation when S i < S f. 

FIGURE 2.26 Fractional flow diagram of Winsor I microemulsion flood at waterflood residual oil saturation,... 

Zhao, B., Zhu, L. and Gao, Y. (2005) A novel solubilization of phenanthrene using Winsor I microemulsion-based sodium castor oil sulfate. /. Hazard. Mater., B119( 1 3), 205-211. 

The ion conductance in a microemulsion depends on its type. In an o/w (Winsor I) microemulsion, the conductance is almost like that of an aqueous medium in a w/o (Winsor II) microemulsion, it is very low, whereas in the bicontinuous (Winsor III) condition, the conductance can be conspicuously large. Depending on the composition and temperature, a dramatic increase in conductance may occur this phenomenon is called percolation. 

Figure 9.18. Variation of the reduced average curvature (//) versus the interfacial molar composition X, with C representing the chain length of the surfactant A H)l = H(X 0)) — jH(X = 0)). The dashed line is calculated with the wedge model , experimental points obtained by phase diagram determination and titration in the Winsor III domain , maximum of solubilization obtained in micellar system A, obtained in a Winsor I microemulsion...

Microemulsions in equilibrium with excess oil or water are classified according to the scheme introduced by Winsor. These two-phase regions are sketched in Fig. 3.18. A Winsor I microemulsion is an oil-in-water system with excess oil, a Winsor II microemulsion is a water-in-oil system with excess water and a Winsor III microemulsion is a middle phase system, with an excess of both water and oil. Winsor III microemulsions are thus used in tertiary oil recovery. Transitions between these phases formed using non-ionic surfactants can be controlled by variation of the HLB through temperature, whereas for ionic surfactants transitions can be driven by changing salt concentration. The temperature at which a microemulsion contains equal amounts of water and oil is termed the phase inversion temperature (PIT). 

Winsor [15] classified the phase equilibria of microemulsions into four types, now called Winsor I-IV microemulsions, illustrated in Fig. 15.5. Types I and II are two-phase systems where a surfactant rich phase, the microemulsion, is in equilibrium with an excess organic or aqueous phase, respectively. Type III is a three-phase system in which a W/O or an O/W microemulsion is in equilibrium with an excess of both the aqueous and the organic phase. Finally, type IV is a single isotropic phase. In many cases, the properties of the system components require the presence of a surfactant and a cosurfactant in the organic phase in order to achieve the formation of reverse micelles one example is the mixture of sodium dodecylsulfate and pentanol. 

At low temperatures an O/W microemulsion (0/Wm) is formed which is in equilibrium with an excess oil phase. This condition is termed a Winsor I system. At high temperatures the headgroup requires less space on the interface and, thus, a negative curvature can result. A phase inversion o ccurs and a W/O microemulsion (W/Om) is formed which is in equilibrium with an excess water phase. This situation is termed a Winsor II system. At intermediate temperatures three phases - a water phase, a microemulsion D and an oil phase - are in equilibrium. This is called a Winsor III system. Here the curvature of the interfaces is more or less zero. Hence, the interfacial tension is minimum as depicted in Figure 3.24 (right) for the system C12E5, tetradecane and water. 

Organic reactions in micro emulsions need not be performed in one-phase systems. It has been found that most reactions work well also in two-phase Winsor I or Winsor II systems, i.e. an oil-in-water microemulsion coexisting with excess oil or a water-in-oil microemulsion coexisting with excess water, respectively [7, 8]. A Winsor III system, i.e. a three-phase system in which a middle phase microemulsion coexists with both oil and water, has also been successfully used as reaction medium [9]. The transport of reactants from the excess oil or water phase to the microemulsion phase, where the reaction takes place, is evidently fast compared to the rate of the reaction. This is a practically important aspect on the use of micro emulsions as media for chemical reactions because it simplifies the formulation work. Formulating a Winsor I or Winsor II system is usually much easier than formulating a one-phase microemulsion of the whole reaction mixture. Winsor systems can also be of value to simplify the work-up process, in particular to separate the product from the surfactant, as will be discussed below in Sect. 2.4 (see also [6]). 

Figure 1 illustrates the use of Winsor I and Winsor II systems as reaction media for the synthesis of 1-phenoxyoctane from sodium phenoxide and 1-bro-mooctane. The reaction was performed in microemulsions based on various... 

Lif and Holmberg have demonstrated the efficiency of microemulsions as a medium for both organic and bioorganic hydrolysis of a 4-nitrophenyl ester see Scheme 3 of Fig. 3 [7]. The reactions were performed in a Winsor I type microemulsion and took place in the lower phase oil-in-water microemulsion. After the reaction was complete a Winsor I—>111 transition was induced by a rise in temperature. The products formed, 4-nitrophenol and decanoic acid, partitioned into the upper oil phase and could easily be isolated by separation of this phase and evaporation of the solvent. The principle is outlined in Fig. 4. The surfactant and the enzyme (in the case of the lipase-catalysed reaction) resided in the middle-phase microemulsion and could be reused. 

In addition to single phase microemulsions, several phase equilibria known as Winsor systems [4] are also shown at low surfactant concentrations. A Winsor I (WI) system consists of an 0/W microemulsion that is in equilibrium with an oil phase, while a Winsor II (WII) system is a W/0 microemulsion in equilibrium with an aqueous phase. A Will system has a middle phase (bicontinuous) microemulsion that coexists with both oil and aqueous phases. 

A new system associated with an 0/W microemulsion for styrene polymerization of up to 15 wt% solids at about 1 wt% DTAB was first reported [65] in 1994. This new two-phase system is rather similar to a Winsor I system, as depicted in Fig. 1 an organic phase containing small portions of water and surfactant in equilibrium with an 0/W microemulsion in the bottom phase. 

Winsor I (organic phase coexisting with an oil in water microemulsion)... 

Lower-phase microemulsion Type ll(-) microemulsion Winsor Type I microemulsion y-type microemulsion Water-external microemulsion... 

In the author s opinion, we should use OAV, bicontinuous, and W/0 microemulsions to describe water-external, bicontinuons, and oil-external microemulsions to be consistent with the terms nsed in emnlsion. In this case, the left lobe (node) and right lobe (node) in a type III phase environment are termed OAV-lobe and W/O-lobe. This book mainly uses two naming systems—(1) type II(-), type III, and type II(-f) (2) Winsor I, Winsor III, and Winsor II—even though other names are sometimes used. The book does not differentiate the name of a microemulsion type from that of the corresponding type of phase environment. 

Hirasaki et al. (1983) assumed that if an excess water phase wets preferentially to a microemulsion phase and a microemulsion phase preferentially to an oleic phase, then (1) in the absence of an excess water phase, the microemulsion is the wetting phase (2) in the absence of an excess oil phase, the microemulsion is the nonwetting phase and (3) when all the three phases are present, the microemulsion is a spreading phase between the excess oil and excess water. Hirasaki et al. (2008) further pointed out that the current understanding of microemulsion phase behavior and wettability is that the system wettability is likely to be preferentially water-wet when the salinity is below the optimal salinity (Winsor I) and is likely to be preferentially oil-wet when the salinity is above the optimal salinity (Winsor II), even in the absence of alkali. Their view is supported by Nelson et al. (1984), Israelachvili and Drummond (1998), and Yang (2000). 

The above-mentioned reaction between sodium phenoxide and 1-bromooctane to synthesise 1 -phenoxyoctane has been carried out in different types of microemulsion systems, all based on the same non-ionic surfactant, Triton X-100 (an octylphenol ethoxylate), the same surfactant concentration (20 wt.%), the same oil to water ratio (2 3) but different hydrocarbons as oil component [28]. This results in different phase volume ratios for the different hydrocarbons. A one-phase microemulsion is only obtained with toluene as oil component. The more hydrophobic oils, i.e. cumene, isooctane, hexadecane and paraffin oil, all give a microemulsion in equilibrium with an excess oil phase, i.e. a Winsor I system. With the more hydrophilic chlorobenzene as oil a microemulsion coexisting with an excess water phase, i.e. a Winsor II system, is obtained. As is also shown in Fig. 5.4, the reactivity is highest in the chlorobenzene- and the paraffin oil-based microemulsions, i.e. in the systems... 

Whereas the surfactant will always reside in the microemulsion phase, the product is likely to partition into an excess oil phase if it is an apolar substance and into an excess water phase if it is a polar compound. The principle is illustrated in Fig. 5.14 for hydrolysis of a lipophilic ester in a Winsor I system (an oil-in-water microemulsion in equilibrium with excess oil) followed by transition into a Winsor III system [60]. The ester partitions between the excess oil phase and the oil droplets and the hydroxyl ions reside in the continuous water domain of the microemulsion. The reaction takes place at the interface. After completed reaction, acid is added to protonate the alkanoate formed and the temperature is raised so that a Winsor I to Winsor III transition occurs. The lipophilic... 

Whereas Winsor III systems exhibit ultra-low interfacial tensions between the three phases and also very high solubilisation capacity, Winsor I systems have higher interfacial tensions and much lower solubilising power. At the transition between the two types of microemulsion systems, an intermediate behaviour can be found which is called supersolubilisation [47,70]. The uptake of oils into surfactant aggregates is usually enhanced by one to two orders of magnitude compared to effective micellar systems, but interfacial tension reduction is still moderate. The transition point can be adjusted by varying the salinity or organic components. 

Preformed microemulsions containing co-solvents and co-surfactants have been used for laboratory experiments [94] and a field test [55] in Canada. The systems were developed for the extraction of a viscous oil containing up to 16% of chlorinated solvents from a site at Ville Mercier. The contaminant is a DNAPL with a density of 1.05 g/cm3 and thus exhibits only a small density difference compared to chlorinated solvents [94]. It could not be extracted effectively by the usual Winsor I systems containing n-butanol as a co-surfactant. The addition of solvents was necessary for effective solubilisation of the contaminant [94]. A preformed microemulsion containing D-limonene, toluene, n-butanol, Hostapur SAS (secondary alkane sulphonate sodium salt) and water was injected into a field test site at Thouin Sand Pit near Montreal. In previous column experiments, a composition of 13.16% D-limonene, 13.16% toluene, 9.21% n-butanol, 9.21% Hostapur SAS and 0.3% of sodium ortho-silicate in water was used as a preformed microemulsion for the extraction of DNAPL from Ville Mercier. 

Baran, J.R., Pope, G.A., Wade, W.H. and Weerasooriya, V. (1996) Water/chlorocarbon winsor I III II microemulsion phase behavior with alkyl glucamide surfactants. Environ. Sci. Technol, 30(7), 2143-2147. 

Analogously, at point C the phase separation into a microemulsion of the composition D and a micellar solution of inverse micelles containing solubilized water takes place. This is a Winsor I (WI) type equlibrium. At the intermediate point E the system consists of a single microemulsion phase (ME). At even lower surfactant concentrations (line c), depending on the water/hydrocarbon ratio, the system will either separate into one of the two-phase systems (Winsor I or Winsor II), or a three-phase system may form at point F. This is a Winsor III (Will) equilibrium with an aqueous phase at the bottom, a microemulsion phase in the middle and a hydrocarbon phase at the top. 

Microemulsion technique is a novel method to prepare ultrafine particles. It has the ability to control the size of particles formed and prevent their aggregation. In a typical study, a water-in-oil (W/0) microemulsion known as Winsor Type II microemulsion has been selected for NS-Ti02 preparation. This technique can provide nanosized particles that are much smaller than an oil-in-water (OAV) or Winsor Type I microemulsion. The procedure to prepare the ultrafine particles by this... 

Scheme 22.5 Different types of microemulsion ( iem) systems according to the concentration of surfactant and the water/oil interfaciai curvature. Wi Winsor I system (0/W iem in equiiibrium with excess oil) ...

There are two types of bipbasic microemulsion systems one with an excess oil in equilibrium with an oil-in-water microemulsion (Winsor I system) and one with an excess water phase in equihbrium with a water-in-oil microemulsion (Winsor... 

Winsor / The microemulsion composition corresponding to Winsor I is characterized by two phases, the lower oil/water (OAV) microemulsion phase in equilibrium with excess oil. 

With nonionic surfactants of the PEO [poly(ethylene oxide)] type, the temperature is an important variable. They are water-soluble at lower temperatures and oil-soluble at high temperatures. In the narrow temperature range where the solubility changes, called PIT (phase inversion temperature [6]), the interfacial tension becomes extremely low, as sketched in Fig. 2. Below the PIT an O/W (oil-in-water) microemulsion is formed, above it a W/O (water-in-oil) microemulsion, with a continuous transition between them, possibly a bicontinuous mixture of oil and water, which at low surfactant concentrations may show a three-phase equilibrium with excess oil and water. Such equilibria are designated Winsor I (O/W-fO), Winsor II (W/O-bW), and Winsor III [(bicontinuous 0-fW)-fO-f W] after P. A. Winsor [7-9], who studied phase equilibria in (mostly ionic) microemulsion systems extensively and at an early date. 

In a Winsor I or Winsor II system (generally called saturated droplet type microemulsions), the interfacial tension, a, of the droplets can be related to the (measurable) macroscopic interfacial tension, y, of the flat interface separating the microemulsion and the excess phase by... 

It is worthwhile to point out that all the equilibria observed in these systems are different from the so-called Winsor equilibria where a microemulsion coexists with an excess oil phase (Winsor I equilibrium, Wl), or an excess water phase (Winsor II equilibrium, WII), or both (Winsor III equilibrium. Will). These equilibria are obtained only by the addition of salt. 

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