Supercritical microemulsions

McFann GJ, Johnston KP (1996) Supercritical Microemulsions. In Kumar P, Mittal KL (eds) Microemulsions Fundamentals and Applied Aspects, in press... 

Supercritical Microemulsions Used as Templates for the Stabilization of Metal Nanoparticles... 

The application of supercritical microemulsions to cleaning is a new area and there have been no published results to date applying these systems to cleaning operations but the combination of surfactants with fluids would be a natural choice for many systems. The information in this chapter is to be used as a guide to the development of cleaning applications based upon supercritical fluid-based microemulsions. 

Pressure-dependent effects can be exploited to significant advantage in a supercritical microemulsion-based cleaning operation. Pressure will have a strong influence on the microstructure of microemulsion phases in compressible fluids as well as on their phase behavior, Microstructure includes the size, shape, and spatial... 

The opportunity to recover the surfactant and extractant following cleaning is a distinct advantage of a supercritical microemulsion over conventional water- or liquid-based systems. The low volatility... 

As this chaper goes to press, there is still more activity in the supercritical microemulsion area. A revieW emphasizing experimental techniques and theoretical explanations has appeared. A recent paper by Johnston et,al. l reports some solubility of a protein in a COj microemulsion. Another paper by Jackson et al. describes the formation of supercritical fluid microemulsions in environmentally friendly CFC s. We expect many more developments in these areas over the next few years. 

Schwan, M. (2005) Uberkritische Mikroemulsionen zur Herstellung nanozellularer Schaume - Principle of Supercritical Microemulsion Expansion (POSME). Ph.D. Thesis, University of Cologne. 

Figure 11.2 Principle of supercritical microemulsion expansion (POSME) [20].

Quantitative predictions of surfactant phase behavior can be made by constructing a thermodynamic model. The classical expression for the free energy of a microemulsion is a function of the interfacial tension, bending moment, and micelle-micelle interactions [47]. Two quantitative models have been developed to describe supercritical microemulsions based on this concept. Here, the key challenge is to find accurate expressions for the oil-surfactant tail interactions and the tail-tail interactions. To do this, the first model uses a modified Flory-Krigbaum theory [43,44], and the second a lattice fluid self-consistent field (SCF) theory [25]. 

The first supercritical microemulsion model [43] was in good agreement with experimental data such as those of Figs. 6 and 7. The model also applies to the one-and two-phase reverse micelle systems of Sec. II. It was found that micelle-micelle interaction effects are dominant in reverse micelle systems where the water/oil ratio is small. However, in the Winsor microemulsion systems described in this section, which have a water/oil ratio near unity, the size of the reverse micelles in the oil phase is determined by natural curvature effects. Micelle-micelle interactions become important at phase transition points, as was observed experimentally in the AOT-brine-propane system [21,23]. The transition between the natural curvature and micelle-micelle interaction mechanisms can be understood in detail on a ternary phase diagram [43]. 

Supercritical microemulsions represent a radically different type of reaction media. Whereas the aqueous microdomains of these systems are much like their analogs in liquid systems, the interfacial region and the continuous-phase solvent have unusual and potentially advantageous properties. The specific benefits include ... 

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