Microemulsion separation

The contact point = c is a critical consolute point. The calculated critical values of the virial coefficient and of the droplet volume fraction (B =-21 and <(ic JO. 13) for a hard-sphere model with an attractive potential are in qualitative agreement with the experimental observations (Figure 2). Around those critical values, a very large turbidity is observed. If the temperature is varied, the microemulsion separates into two turbid microemulsions. Angular variations of the scattered intensity and of the diffusion coefficient are observed (16) but the correlation function remains exponential. All these features are characteristic of the vicinity of a critical consolute point. The data can be fitted with theoretical predictions (17) ... 

A typical spectrum, recorded at 22.5 MHz for a microemulsion containing a 67% excess of MMA, is shown in Figure 5. Except for the carbons in the middle of the SLS chain, each type of carbon gave rise to a single, distinct resonance signal. The assignments shown for the carbons of MMA and hexanol were determined by running each of the components of the microemulsion separately. 

Figure 1.14(a) shows the phase prism of the system water-oil-non-ionic surfactant (already shown in Fig. 1.3) together with the temperature dependence of the interfacial tensions (Fig. 1.14(b)). As discussed in Section 1.2.1, at low temperatures, non-ionic surfactants mainly dissolve in the aqueous phase and form an oil-in-water (o/w) microemulsion (a) that coexists with an oil-excess phase (b). Thus, for temperatures below the temperature T the interfacial tension three-phase body. Thus, three different interfacial tensions occur within the three-phase body, namely the interfacial tension between the water-rich and the surfactant-rich phase crac, between the oil-rich and the surfactant-rich phase oyc, and between the water-rich and the oil-rich phase uab. However, the latter can only be measured if most of the surfactant-rich middle phase (c) is removed, which then floats as a lens at the water/oil interface. Increasing the temperature one observes that the three-phase body vanishes at the temperature Tu, where a water-in-oil (w/o) microemulsion is formed by the combination of the two phases (c) and (b). Therefore, at temperatures above Tu the interfacial tension crab refers to the interface between a w/o-microemulsion and a water-rich excess phase. 

Cheng, H. andSabatini, D.A. (2002) Phase-behavior-based surfactant-contaminant separation of middle phase microemulsions. Separation Sci. Technol., 37(1), 127-146. 

Use of microemulsions has been proposed for the synthesis of zeolites, their confined spaces acting as nanoreactors for growth [146]. The concept works with branched chain surfactant molecules at low temperature (368 K for 96 h), yielding silicalite-1 (MFI) crystals with narrow sizes tunable between 240 and 540 nm. Salt content is the morphology-determining parameter, which is consistent with the salt screening of the surfactant-electrostatic forces [147]. The zeolite does not nucleate in the microemulsion, and not before amorphous silica formed in the microemulsion separates from this medium. Whereas in conventional silicalite-1 synthesis conditions (433 K), the morphology is only sensitive to the electrostatic forces between the silicate and the surfactant... 

The presence of a chromophore group in the hydrophilic or hydrophobic moieties in the surfactant molecular structure makes it sensitive to different physical responses, in particular, for the control of physicochemical parameters of colloidal systems such as surface activity, aggregation structure, viscosity, microemulsion separation, and solubilization. 

In our studies, swell was the most significant problem. For example, typical experiments for the microemulsion separation of mercury would start with an internal... 

Microemulsions are treated in a separate section in this chapter. Unlike macro- or ordinary emulsions, microemulsions are generally thermodynamically stable. They constitute a distinctive type of phase, of structure unlike ordinary homogeneous bulk phases, and their study has been a source of fascination. Finally, aerosols are discussed briefly in this chapter, although the topic has major differences from those of emulsions and foams. 

D. O. Shah and W. C. Hsieh, Microemulsions, Liquid Crystals and Enhanced Oil Recovery, in Theory, Practice, and Process Principles for Physical Separations, Engineering Foundation, New York, 1977. 

Many solutions of common nonionic surfactants and water separate into two phases when heated above a certain temperature (the cloud point), and some investigators call the phase of greater surfactant concentration, a microemulsion. Thus, there is not even universal agreement that a microemulsion must contain oil. 

A (macro)emulsion is formed when two immiscible Hquids, usually water and a hydrophobic organic solvent, an oil, are mechanically agitated (5) so that one Hquid forms droplets in the other one. A microemulsion, on the other hand, forms spontaneously because of the self-association of added amphiphilic molecules. During the emulsification agitation both Hquids form droplets, and with no stabilization, two emulsion layers are formed, one with oil droplets in water (o /w) and one of water in oil (w/o). However, if not stabilized the droplets separate into two phases when the agitation ceases. If an emulsifier (a stabilizing compound) is added to the two immiscible Hquids, one of them becomes continuous and the other one remains in droplet form. 

Liquid Crystal Third Phase. In addition to micelles and microemulsion droplets, surfactants may form Hquid crystals. A Hquid crystal is a separate phase, which comes out of solution, not like the micelles or microemulsion droplets, which are microscopic entities within the solution. 

The use of surfactants has been an important positive factor for several reasons. They form O/W microemulsions, which must have low viscosity and contain a high oil content later on this oil must be separated fairly easily. 

The influence of pH, ionic strength, and protein concentration on the extraction of a-lactalbumin and 3-lactoglobulin from an aqueous solution with water/AOT/isooctane microemulsions and their separation has been reported [168],... 

Since some structural and dynamic features of w/o microemulsions are similar to those of cellular membranes, such as dominance of interfacial effects and coexistence of spatially separated hydrophilic and hydrophobic nanoscopic domains, the formation of nanoparticles of some inorganic salts in microemulsions could be a very simple and realistic way to model or to mimic some aspects of biomineralization processes [216,217]. 

Hilder, E.F. et al.. Separation of hydrophobic polymer additives by microemulsion electrokinetic chromatography, J. Chromatogr A, 922, 293, 2001. 

Other examples of organized molecular assemblies of interest for photocatalysis are (1) PC-A, PC-D or D-PC-A molecules where PC, A and D fragments are separated by rigid bridges (2) host-guest complexes (3) micelles and microemulsions (4) surfactant monolayers or bilayers attached to solid surfaces, and (5) polyelectrolytes [19]. 

Depicted in Fig. 2, microemulsion-based liquid liquid extraction (LLE) of biomolecules consists of the contacting of a biomolecule-containing aqueous solution with a surfactant-containing lipophilic phase. Upon contact, some of the water and biomolecules will transfer to the organic phase, depending on the phase equilibrium position, resulting in a biphasic Winsor II system (w/o-ME phase in equilibrium with an excess aqueous phase). Besides serving as a means to solubilize biomolecules in w/o-MEs, LLE has been frequently used to isolate and separate amino acids, peptides and proteins [4, and references therein]. In addition, LLE has recently been employed to isolate vitamins, antibiotics, and nucleotides [6,19,40,77-79]. Industrially relevant applications of LLE are listed in Table 2 [14,15,20,80-90]. 

Fatty alcohol- (or alkyl-)ethoxylates, CoE, are considered to be better candidates for LLE based on their ability to induce rapid phase separation for Winsor II and III systems. (Winsor III systems consist of excess aqueous and organic phases, and a middle phase containing bicontinuous microemulsions.) However, C,E,-type surfactants alone cannot extract biomolecules, presumably because they have no net negative charge, in contrast to sorbitan esters [24,26,30,31]. But, when combined with an additional anionic surfactant such as AOT or sodium benzene dodecyl sulfonate (SDBS), or affinity surfactant, extraction readily occurs [30,31]. The second surfactant must be present beyond a minimum threshold value so that its interfacial concentration is sufficiently large to be seen by... 

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