Mixed micelles pressure dependence

Sugihara et al. [132] investigated the effect of chain length on the pressure dependence of micellization in mixed-surfactant solutions of nonyl-V-methylglu-... 

One interesting feature of the functional form derived here is the direct relationship of the activity coefficients and composition between the micellar and surface psuedo-phases. This allows a comparison of nonideal interactions in the micelle and monolayer as modeled by their respective net interaction parameters. In principle, this form may also allow extension to more complicated situations such as the treatment of contact angles in nonideal mixed surfactant systems. Here, the functional form derived above depends on differences in surface pressures and these may be directly obtained from experimentally measured parameters under the proper conditions (30). 

Amphiphiles, the representatives of which are soap, surfactant and lipid, have a hydrophilic polar head and lipophilic nonpolar tails. They always remain on the interface between water and oil and form monolayers of surfactants in a water/oil/amphiphile ternary system. This monolayers or interfacial film reduce the surface tension between water and oil domains. In a three-component system the surfactant film exists in various topologically different structures such as micelles, vesicles, bicontinuous microemulsions, hexagonal arrays of cylinders or lamellar structures depending upon the pressure, temperature and the concentration of the components [1,2]. Microemulsions are thermodynamically stable, isotropic and transparent mixtures of ternary amphiphilic systems. When almost equal volume fractions of water and oil are mixed with a dilute concentration of surfactants, they take... 

More recently, titanium dioxide particles have been produced using supercritical CO2 (77). In this case, carbon dioxide is used as the organic phase of the microemulsion. Two containers were placed inside a pressure vessel with one container partially filled with an alkoxide precursor and the other with a solution of water and fluorinated surfactants. The vessel was then pressurized with carbon dioxide and heated until supercritical conditions were attained. The alkoxide is soluble in carbon dioxide, and the aqueous surfactant solution forms a stable microemulsion with the supercritical carbon dioxide. Over time, the alkoxides mix with the micelles and react with the water to form titanium dioxide. The product characteristics depend significantly on the solubility of the alkoxides in supercritical carbon dioxide. 

The phenomenon of a surfactant exhibiting a maximum T2 appears to be a general behavior, and perhaps other anionic or cationic surfactants may form tightly packed micelles at their own characteristic concentrations. As with the first cmc, this critical concentration may also depend upon physical and chemical conditions such as temperature, pressure, pH, salt concentration, and other parameters in addition to the molecular structure of the surfactant [24,25], Work is currently in progress at the CSSE on identifying a similar critical concentration for nonionic surfactants as weU as mixed surfactant systems. 

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