Analysis microemulsion structure

The preceding analysis assigns an important role to the interaction between droplets or equivalently the fluidity of the interfacial region in the microemulsions structure. 

Efficiency. The peak efficiencies obtained with the L2 microemulsion mobile phases for various solutes were compared to the ones obtained with classical hexane-2-propanol phases. A 2- to 3-fold lower plate count was obtained with the L2 microemulsion mobile phases compared to the traditional mobile phases [6]. In another work, the efficiency obtained with the heptane-AOT-water microemulsion was in the 200 plate range, 10 times lower than the values obtained for the same solutes and the same column with traditional heptane-propanol phases [7]. Once again, the exchange of the solute between the stationary phase and the reversed micelles is slow. The efficiency problem in the case of microemulsion mobile phases is so serious that the practical use of these mobile phases in chemical analysis is questionable [8]. For physicochemical research such as microemulsion structure investigation, MLC can help. 

Microemulsions form spontaneously in much the same way as structural elements, such as surfactant micelles, rearrange themselves following the addition of the cosurfactant. Because the water may be incorporated into the hydrophilic structures of reverse micelles, when examined by x-ray analysis spherical droplets with diameters of 6-80 nm have been reported. 

Such an analysis is appropriate and useful for non-associated solutions in which the diffusion coefficients are constant and hence, meaningful. In the present system the association structures vary in a pronounced manner in the W/0 microemulsion region (21-23) and the transfer from one phase to another of a component may strongly influence the flue. With this in mind no attempts were made to calculate the... 

This model calculation illustrates a recurring theme in this book the notion of an intrinsically preferred curvature implies profound consequences for structure. The analysis of mesostructure of these microemulsions is helped by the fact that DDAB resides exclusively at the interface. In many microemulsions this is not the case, so that more detailed calculations are... 

The conclusions drawn on the basis of the dielectric loss analysis of liquid samples, support the interpretation that a very gradual confluence of the different types of dispersions takes place.Such an interpretation could explain the instauration of polydispersed samples in terms of the coexistence, at equilibrium, first, of micellar aggregates with w/o microemulsion droplets and, successively, of a microemulsion with l-I O-per hydrophilic group monolayer, in equilibrium with a hydrated type of microemulsion (U-water molecule per polar head of the surfactant hydrophilic groups monolayer). The latter interpretation is in accordance with Steinbach and Sucker findings that the two types of structures ( 1-HpO and U-HgO molecule), may coexist at equilibrium (23.). 

Finally, a quench into the one-phase region of the microemulsion has been investigated. An analysis based on a Ginzburg-Landau model for a single, conserved order parameter predicts [160] that the equal-time structure factor, Eq. (65), approaches its equilibrium form S(k) algebraically for long times t. 

In the bilayer continuous structures occurring in the bicontinuous cubic and L3 phases, the diffusion can be described by essentially the same equations. Finally, we note that Eqs. (4)-(6) have been applied to the analysis of self-diffusion data from a number of bicontinuous microemulsions, L3 phases, and bicontinuous cubic phases [34-36]. 

The fluorescence emission spectrum of ANS depends strongly on the polarity of the environment, with a red shift of the emission maximum in more polar media. Therefore this probe has been used to obtain information on the shell-like structuring in the interior of microemulsion water droplets [73]. Fluorescence spectroscopy can often be used to obtain information on the location of additives in microemulsions [70]. A change in the emission intensity or in the wavelength of the emission maximum indicates interactions of the probe with the interfacial layer, either direct or indirect. From a comparative analysis of the fluorescence spectra of labeled enzyme it was concluded that hydrophobically modified probes were forced toward the interface [77]. 

Microemulsions are the only systems which can cosolubUize high concentrations of both water-soluble and water-insoluble reactants and thus render themselves as a novel medium for chemical synthesis the structure of the microemulsions critically determines the reaction parameters. The reactivity in microemulsions is discussed in Chapter 15 by Bunton and Romsted. The utility of microemulsions in spectroscopic analysis is described in Chapter 16 by Guo and Zhu. 

Microporous zincophosphate crystals of zeolitic structure have been synthesized by Dutta and colleagues [335, 222] via multiple microemulsions. In the first investigation [335], these authors used two reverse microemulsions, based on the system AOT/n-hexane, containing (a) aqueous solution of Zn(N03)2.6H20 and (b) aqueous solution with H3PO4 and tetramethylammonium hydroxide (the latter was required for incorporation of the phosphate in the reverse micelle). For the Zn-micelle, the [AOT]/[H20] ratio was 13, while for the phosphate-micelle, the value went up to 21. Uptake of the constituents in the micelles was examined by chemical analysis. The two microemulsions were finally mixed at room temperature. Particles grew from 14 nm to - 150 nm in three days, and then became stable at --140 nm. 

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