Theories microemulsions

These fascinating bicontinuous or sponge phases have attracted considerable theoretical interest. Percolation theory [112] is an important component of such models as it can be used to describe conductivity and other physical properties of microemulsions. Topological analysis [113] and geometric models [114] are useful, as are thermodynamic analyses [115-118] balancing curvature elasticity and entropy. Similar elastic modulus considerations enter into models of the properties and stability of droplet phases [119-121] and phase behavior of microemulsions in general [97, 122]. 

S. A. Safran, Theory of Structure and Phase Transitions in Globular Microemulsions, in Micellar Solutions and Microemulsions, S. H. Chen and R. Rajagopalan, eds.. Springer-Verlag, New York, 1990, Chapter 9. 

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. 

Shah D O (ed) 1985 Macro- and Microemulsions—Theory and Applications (Washington, DC American Chemical Society)... 

Modem scaling theory is a quite powerful theoretical tool (appHcable to Hquid crystals, magnets, etc) that has been well estabUshed for several decades and has proven to be particularly useful for multiphase microemulsion systems (46). It describes not just iuterfacial tensions, but virtually any thermodynamic or physical property of a microemulsion system that is reasonably close to a critical poiat. For example, the compositions of a microemulsion and its conjugate phase are described by equations of the foUowiug form ... 

D. O. Shah, Macro and Microemulsions Theory and Applications, American Chemical Society, Washington, D.C., 1985. 

It must be pointed out that formation and stabihzation of nanoparticles in reversed micelles are the result of a delicate equilibrium among many factors. In addition, lacking a general theory enabling the selection a priori of the optimal conditions for the synthesis of nanoparticles of a given material with the wanted properties, stable nanoparticles containing w/o microemulsions can be achieved only in some system-specific and experimentally selected conditions. 

Lagues et al. [17] found that the percolation theory for hard spheres could be used to describe dramatic increases in electrical conductivity in reverse microemulsions as the volume fraction of water was increased. They also showed how certain scaling theoretical tools were applicable to the analysis of such percolation phenomena. Cazabat et al. [18] also examined percolation in reverse microemulsions with increasing disperse phase volume fraction. They reasoned the percolation came about as a result of formation of clusters of reverse microemulsion droplets. They envisioned increased transport as arising from a transformation of linear droplet clusters to tubular microstructures, to form wormlike reverse microemulsion tubules. 

Before describing how microemulsion nature and structure are determined by the structure and chain length of surfactant and cosurfactant, it is necessary first to briefly review the theories of microemulsion formation and stability. These theories will highlight the important factors required for microemulsion formation. This constitutes the first part of this review. The second part describes the factors that determine whether a w/o or o/w microemulsion is formed. This is then... 

The influence of surfactant structure on the nature of the microemulsion formed can also be predicted from the thermodynamic theory by Overbeek (17,18). According to this theory, the most stable microemulsion would be that in which the phase with the smaller volume fraction forms the droplets, since the osmotic term increases with increasing i. For w/o microemulsion prepared using an ionic surfactant, the hard sphere volume is only slightly larger than the water volume, since the hydrocarbon tails of the surfactant may interpenetrate to a certain extent, when two droplets come close together. For an oil in water microemulsion, on the other hand, the double layer may extend to a considerable extent, depending on the electrolyte concentration... 

Robbins, M. L., "Theory for the Phase Behaviour of Microemulsions", Paper No 5839, presented at the Improved Oil Recovery Symposium of the Society of Petroleum Engineers of AIME, Tulsa, Oklahoma, March 22-24 (1976). 

Bansal, V.K., Shaw, D.O. Microemulsions, Theory and Practice" edited by Prince, L.M., Academic Press, New York, 1977, chapter 7. 

Altria, K.D. (2000). Background theory and applications of microemulsion electrokinetic chromatography. J. Chromatogr. A 892 171-186. 

Romsted LS (1977) A general kinetic theory of rate enhancements for reactions between organic substrates and hydrophUic ions in micellar systems. In Mittal KL (ed) Micellization, Solubilization, Microemulsions. Plenum Press, New York... 

Enzyme activity is highly dependent on the composition, and as a consequence on different microstructures of the microemulsion. Up to the present, no suitable theory exists to explain the correlation between the reaction media properties and their effects on enzymatic reactions in microemulsions. All experimental results on enzymatic reactions show that the activity is greatly affected by the structure of the microemulsion. 

The basic kinetic model for enzyme catalysed conversions in water and in w/o-microemulsions is based on the theory of MichaeHs and Menten [83]. Although the Michaelis-Menten-model is often sufficient to describe the kinetics, the bi-bi-models (e. g. random bi-bi, orderedbi-bi or ping-pongbi-bi), which describe the sequences of substrate bindings to the enzyme are the more accurate kinetic models [84]. 

The effectiveness of the method is most probably based on the fact that alkyl hypochlorite is formed at the oil/water interface where the cosurfactant alcohol resides. The oxidation that follows takes place either inside or on the surface of oil droplet. The rate of the reaction can result from a large hydrocarbon/water contact area permitting interaction between oil-soluble sulfide with interfacial cosurfactant that served as an intermediary. An extension ofthis procedure to mustard deactivation has also been proposed [20b]. Such systems could be also applied to the degradation of several environmentally contaminating materials The formation of microemulsions, micelles and vesicles is promoted by unfavourable interactions at the end sections of simple bilayer membranes. There is no simple theory of solute-solvent interactions. However, the formation of... 

The effect of AB diblock size relative to the homopolymers on the compati-bilization of A/B homopolymer blends was examined using numerical self-consistent field theory (in two dimensions) by Israels et al. (1995). They found that the interfacial tension between homopolymers can only be reduced to zero if the blocks in the diblock are longer than the corresponding homopolymer. Short diblocks were observed to form multilamellar structures in the blend, whereas a microemulsion was formed when relatively long copolymers were added to the homopolymer mixture. These observations were compared to experiments on blends of PS/PMMA and symmetric PS-PMMA diblocks reported in the same paper. AFM was used to measure the contact angle of dewetted PS droplets on PMMA, and the reduction in the interfacial tension caused by addition of PS-PMMA diblocks was thereby determined. The experiments revealed that the interfacial tension was reduced to a very small value by addition of long diblocks, due to emulsification of the homopolymer by the diblock, in agreement with the theoretical expectation (Israels et al. 1995). 

Robbins, M., The Theory of Microemulsions," AlChE Meetg., Tulsa, Okla.,... 

Hng, T.F. Lee, H.K. Shah, D.O. in Industrial Applications of Surfactants, Karsa, D.R. (Ed.), Royal Society of Chemistry London, 1987. Prince, L.M. (Ed.) Microemulsions Theory and Practice, Academic Press New York, 1977. Tadros, Th.F. Surface Chemistry in Agriculture in Handbook of Applied Surface and Colloid Chemistry, Holmberg, K. (Ed.), Vol. 1, Wiley New York, 2001, pp. 73-83. 

Shah, D.O. (Ed.), Macro- and Microemulsions Theory and Applications American Chemical Society Washington, 1985. 

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