Structures spherical reverse micellar

Figure 4.11 Schematic representation of spherical reverse micellar structure formed in discontinuous cubic (b) phase. The radius of the micelle is r, the radius of the hydrophilic...

The liquid gelators, Span 80-Tween 80 also forms emulsion organogels and emulsion hydrogels by fluid-filled fiber mechanism. It has been reported that Span 80 (sorbitan monooleate) and Tween 80 (polyoxyethylene sorbitan monooleate) mixed in the ratio of 1 2 w/w forms organogel with better firmness and architecture as compared to the other surfactant mixture ratios.When water is added dropwise into the homogenous surfactant mixture and oil, it forms spherical reverse-micellar droplets. These droplets/fibers self-assemble to form three-dimensional architecture to immobilize apolar solvent. " Similarly, in case of hydrogels micellar structures are formed, which entraps the external liquid phase to flow and form hydrogel. 

In the past few years, a range of solvation dynamics experiments have been demonstrated for reverse micellar systems. Reverse micelles form when a polar solvent is sequestered by surfactant molecules in a continuous nonpolar solvent. The interaction of the surfactant polar headgroups with the polar solvent can result in the formation of a well-defined solvent pool. Many different kinds of surfactants have been used to form reverse micelles. However, the structure and dynamics of reverse micelles created with Aerosol-OT (AOT) have been most frequently studied. AOT reverse micelles are monodisperse, spherical water droplets [32]. The micellar size is directly related to the water volume-to-surfactant surface area ratio defined as the molar ratio of water to AOT,... 

Reverse micelles are small (1-2 nm in diameter), spherical surfactant aggregates huilt in an apolar solvent (usually referred to as oil), whereby the polar heads form a polar core that can contain water - the so-called water pool. The connection with autopoiesis is historically important, because it was with the collaboration with Francisco Varela that the work started (in fact it began as a theoretical paper - see Luisi and Varela, 1990). The idea was this to induce a forced micro-compartmentalization of two reagents, A and B, which could react inside the boundary (and not outside) to yield as a product the very surfactant that builds the boundary (Figure 7.13). The product S would concentrate at the membrane interface, which increases its size. Since reverse micelles are usually thermodynamically stable in only one given dimension, this increase of the size-to-volume ratio would lead to more micelles. Thus the growth and multiplication would take place from within the structure of the spherically closed unit, be governed by the component production of the micellar structure itself, and therefore (as will be seen better in... 

Figure 9.8 Micellar structures (A = spherical micelle, B = cylindrical micelle, C = bilayer lamellae, D = reverse micelle, E = biconlinuous cubic phase, F = vesicular-liposomes). (Reproduced with permission from D. F. Evans and H. Wennersttom, eds.. The Colloidal Domain. Where Physics, Chemistry, Biology and Technology Meet. Wiley-VCH, Weinheim, 1984. Cop5fright 1984 Wiley.)...

Surfactant molecules in solution beyond their critical micelle concentration (CMC) are widely known to form aggregates in different shapes. Below the CMC, surfactants in solution are present in the form of individual molecules. Figure 3 illustrates the formation of various association structures with increasing surfactant concentration- It is likely that surfactant molecules may form spherical, cylindrical, hexagonal, lamellar and reversed micellar (e.g. spherical) structures in solution by adjusting the proper physicochemical conditions such as pH, temperature and the presence of various electrolytes. If oil is present in the system, these association structures can solubilize the oil, and can produce a clear, thermodynamically stable system. Depending on the nature of the oil phase and the oil/water ratio, the oil can be a continuous or disperse phase in the system. 

While the microemulsion method has been widely applied to the production and stabilization of spherical metal particles with various sizes and compositions, shape control of noble metallic particles using this procedure has only been demonstrated in a handful of studies to date. Pileni and co-workers demonstrated that it is possible to control nanocrystal shape to some extent within microemulsions.Although the shape of the templates plays a role during the growth of the nanocrystals, these authors showed that the particle shape can be controlled even if the microscopic structure of the self-assembled surfactant system used as a template remains unchanged and that addition of salt to the templates can induce drastic changes in the particle shape. Recently, the same group also reported the synthesis of silver nanodisks in reverse micellar solution by reduction of Ag(AOT) with hydrazine, with various sizes that depended on the relative amount of hydrazine, but with constant aspect ratio. 

However, these experimental approaches appeared to be relevant enough to form the basis of the first thermodynamic treatment of the solubilization of protein in reversed micelles developed by Caselli et. (58). The micellar phase before solubilization forms the reference state of thermodynamic calculations. According to the structural model of spherical monodisperse droplets, the knowledge of the micelle radius and density completely characterizes the system. The uptake of protein is made... 

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