Minimum water solubilization microemulsion

Figure 9 can be made more universal in character by replacing solvent density with solvent dielectric constant. In such a plot, not only branched alkanes but also the noble gases krypton and xenon form a continuous envelope of of the same general shape as that seen in Fig. 9. The dielectric constant at which the maximum ITq is found corresponds to a minimum in the attractive dispersion interaction between microemulsion droplets as calculated from Lifshitz theory [21]. Therefore, reverse micelles would be most resistant to phase separation caused by micelle-micelle interactions at this point, and solubilization of water would reach a maximum. However, it seems unlikely that the dispersion interaction would be the sole contributor to IFq behavior [14,43].

It is well established that in order to obtain a stable nucleus, a cluster containing a critical number of monomers ( c) must form [126-128]. It follows, therefore, that for microemulsion-mediated synthesis, if the water pools are viewed as isolated microreactors, then a relevant question is, How many of the available water pools contain the minimum number of monomers needed for nucleation Here the concept of occupancy number ( oc) is helpful [13]. For a reactant solubilized in the reverse micellar pseudophase, the quantity Hoc represents the number of solubilisate molecules present in a given water pool. 

The first step in selecting an optimal micellar system for any field application is to define a complete one-phase microemulsion without any oil or water phase separation, whose viscosity is in the range of the equivalent viscosity of the oil-bank, and which can be prepared from a minimum amount of surfactant, corresponding to the smallest multiphase area in phase diagrams or to the highest solubilization parameters. Such a system involves a surfactant... 

A temperature study of the low-frequency conductivity of water-in-undecane microemulsions using as the surfactant a blend of octylphenylether polyoxyethylenes showed that, as the temperature increases, the conductivity decreases down to a minimum whose temperature coordinate was found to be equal systematically to the solubilization-end temperature corresponding to the system water content. Water-in-dodecane systems exhibited the same behavior. 

For example, using the same system highlighted above (Ci2E5/octane/water), the interfacial tension between oil and water as a function of temperature exhibits a sharp inverted cusp, with the minimum and ultra-l( interfacial tension (5 x 10 " mN m ) found at T (Figure 4.15(c)). Optimally formulated microemulsions with high solubilization of oil and water exhibit the lowest interfacial tensions. Note, however, that the interfacial tension curves and the characteristic sizes exhibit exactly the opposite dependence as the mean curvature changes (see Figure 4.15). 

To determine complete ternary phase diagrams, in particular at a number of different temperatures, is a lengthy process, and has been carried out for only for a few systems. Rather, one often reduce the number of composition degrees of freedom by one and studies a planar section through the phase prism. The section defined by 0vv = 0o ( fish-cut ) is shown schematically in Figure 17.3. In this section, one can determine 7] and Tu and the minimum amount of surfactant necessary to solubilize equal amounts of water and oil, which we here denote as 0. The lower 0, then the more efficient is the surfactant. We see also that the microemulsion at higher surfactant concentrations is in equilibrium with a lamellar phase (L ), a typical feature of long-chain surfactants. 

As seen in Fig. 20, the solubilization parameter curves cross over at exactly the same formulation (here salinity) where the interfacial tension curves do it, which is expected if the Hu relationship strictly applies. At this point, which is by definition the optimum formulation of the scan, the microemulsion is solubilizing the same amoimt of oil and water (as V = Vw) and its representative point on a SOW diagram is exactly at the same distance from the W and O vertices. As seen in Fig. 20, the solubilization increases from both sides when the formulation tends to the optimum one. The value of the solubilization parameter at optimum is generally referred to as SP (the maximum of the minimum of the Vq/Vs and Vw/Vs ratios that is attained at Vq/Vs = It is worth noting that SP ... 

It is believed that the formation of a microemulsion can enhance detergent action since the oil-water interfacial tension can be lowered considerably, which facilitates solubilization of oily dirt particles by surfactant. The microemulsion is of Winsor type III (Section 3.13.2), with small amounts of surfactant forming a middle phase microemulsion in equilibrium with excess oil and water. The oil-water interfacial tension is a minimum at the phase inversion temperature (PIT) of an oil-water-surfactant system, so it is desirable to optimize the properties of the detergent mixture so that the system is close to the PIT at the washing temperature. Microemulsions made from mixtures of nonionic surfactants are used in hard surface cleaning products. Usually they are sold in concentrated form and diluted prior to use. 

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