Physicochemical properties of micellar

PHYSICOCHEMICAL PROPERTIES OF MICELLAR MEDIA J Gouy-Chapman layer... 

PHYSICOCHEMICAL PROPERTIES OF MICELLAR MEDIA Table 2.7 Kraflft Point ( C) of Some Surfactants [13],... 

Sometimes, the physicochemical properties of ionic species solubilized in the aqueous core of reversed micelles are different from those in bulk water. Changes in the electronic absorption spectra of ionic species (1 , Co ", Cu " ) entrapped in AOT-reversed micelles have been observed, attributed to changes in the amount of water available for solvation [2,92,134], In particular, it has been observed that at low water concentrations cobalt ions are solubihzed in the micellar core as a tetrahedral complex, whereas with increasing water concentration there is a gradual conversion to an octahedral complex [135],... 

The ability of micelles or related aggregates to alter reaction rates and selectivity has been an area of active research for the past several decades. Reactants are partitioned into the aggregates by coulombic and hydrophobic interactions the observed rate accelerations are largely a result of the increased localization of the reactants and also of the typical physicochemical properties of the micellar environment, which are significantly different from those of the bulk solvents. This unique ability of the aggregate systems has therefore prompted several scientists to employ micellar media for catalytically carrying out specific reactions. 

Recently, novel micellar systems based on block copolymers have been developed for drug solubilization and delivery (Houlton, 2003). One example of such a system is poly-ethylene glycol-poly-aspartic acid block copolymer, which spontaneously forms into colloidal particles (micelles) in aqueous solution. In this type of micelle, the drug molecule will experience an environment characterized by the physicochemical properties of the polymer (see Section 16.2.2.3). 

Ultimately, the water pool and the interfacial surfactant layer can exhibit multiple catalytic effects, which result from the concentrations of reactants localized in the nano-compartmentalized region and the physicochemical properties of the micellar environment. Accordingly, the reversed micellar systems have the possibility of controlling the multiple effects on the reactions by changing the physical factors of the reversed micellar systems such as water mobility, micropolarity, and electrostatic force. 

The knowledge of the physicochemical properties of the micellar phases is required in order to use them properly. This is outlined in the following chapter. The use of surfactants in chromatography was first implemented in ion-pair chromatography. This lead to the employment of... 

Sodium dodecyl sulfate is the most commonly used surfactant in MLC. However, there are several thousand varieties of surfactants and many of them can be used as well. Appaidix II tabulates tiie physicochemical properties of selected surfactants. A collection of micellar partitioning coefficients gathered fi-om the MLC literature are also given in Appendix III. Finally, Appendix IV shows examples of phase diagrams of a few systems relevant in MLC and the simplest way to make one that cannot be found in the literature. 

It is well known that surfactant molecules (ions) can aggregate to form micelles on reaching a fixed concentration (cmc) in the solution [11]. The formation of such aggregates leads to the abrupt changes of physicochemical properties of the surfactant solution. Numerous methods based on the difference between the properties of monomer and micellar solutions can be employed for the estimation of cmc values [12]. We used conductivity and surface tension methods to determine the cmc of DDPB and Teflon wetting and surface tension methods for TX. The results of the cmc estimation are listed in Table 2. 

---