Micelles solubilisate location

In retrospect, this study has demonstrated the limitations of two commonly accepted methods of analysing solubilisation and micellar catalysis, respectively. It has become clear that solubilisate ririg-current induced shifts need to be interpreted with due caution. These data indicate a proximity of solubilisate and parts of the surfactant and, strictly, do not specify the location within the micelle where the encounter takes place. Also the use of the pseudophase model for bimolecular reactions requires precaution. When distribution of the reactants over the micelle is not comparable, erroneous results are likely to be obtained... 

Figure 3 Schematic two-dimensional simplified representation of a proposed spherical zwitterionic micelle containing the Rh/15 catalyst. The hydrocarbon chains of the tenside phosophine (-CH2-CH-(CH2)n-CH3), the hydrophilic head group (-S03 ), the counter ions (Na+ and OH, depicted as X) and the solubilised 1-tetradecene (dotted part, core of the micelle) are schematically indicated to denote their relative locations and not their configuration, number, distribution or relationship to the molecular sizes.

In micellar catalysis, reactant must be solubilised at a location near to the micelle surface where it is accessible to reagent in the aqueous... 

Solubilisates that are located within the micellar core increase the size of the micelles in two ways. Micelles become larger not only because their core is enlarged by the solubilisate but also because the number of surfactant molecules per micelle (the aggregation number) increases in an attempt to cover the swollen core. Solubilisation within the palisade layer, on the other hand, tends not to alter the aggregation number, the increase in micellar size resulting solely from the incorporation of solubilisate molecules. 

An important property of surfactant micelles is their ability to solubilise water-insoluble compounds. The location of solu-bilisates in the micelles is closely related to the chemical nature of the solubilisate in... 

It would be of great interest if water could be dispersed in the polar cores of the systems described above. Water was added to the binary systems (W=[H20]/[TX]=5), with an additional amount to account for the small water solubility in CO2. In some cases added water caused the precipitation of the surfactant Near-Infrared (NIR) spectra obtained for the Triton surfactants, and interpreted as in ref. 13, indicated no clear evidence of water solubilisation in the micelles and the signals were consistent with water mainly located in the bulk CO2. Further attempts with brine (0.05 and 0.10 mol dm ) proved to be no more successful. 

For polymerisation in a normal emulsion, the hydrophobic monomer is dispersed in the aqueous phase, in which it is almost completely insoluble, with the help of a surfactant. On the whole it is then located in the form of reservoir droplets of diameter d 1-10 gm, and in surfactant micelles of diameter d 5-10 nm. A small fraction may be solubilised in the continuous aqueous phase. The initiator is generally present in the aqueous phase (see Fig. 6.5). Polymer particles are generated by two simultaneous processes. The first is free radical capture by micelles, called micellar nucleation. There are far fewer droplets than micelles and the total surface area of the micelles is extremely large. Consequently, radicals tend to penetrate micelles rather than monomer droplets. The latter act mainly as monomer reservoirs. The second of the processes mentioned above is the formation of oligomer radicals in the continuous phase, and is referred to as homogeneous nucleation. When radicals reach a certain size, they become insoluble and group together to form polymer particles similar to those formed by micellar nucleation. 

The site of incorporation of solubUisate is closely related to its chemical stmcture (Eigure 13.21). Although in many cases a particular location is preferred, the lifetime of a solubilisate within the micelle is long enough for a rapid interchange between different locations. 

Insoluble a.i. requires solubilization into surfactant micelles. This involves the formation of a thermodynamically stable, isotropic solution, by the introduction of an amphiphilic component(s). Solubilization is affected by the structure of the surfactant and the solubilisate, temperature, and addition of electrolytes and nonelectrolytes. The structural characteristics of the surfactant influence its solubilizing capacity, particularly with regard to the existence of different solubilization sites within the micelles. In cases in which insoluble a.i. are located either in the micelle core or deeply within the micelle, solubilization should increase with increase in the alkyl chain length of the surfactant. If solubilization occurs in the hydrophilic portion of the surfactant, it will increase in accordance with the size of that group solubilization is influenced also by polarity, chain branching, and molecular size, shape, and structure. ... 

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