Solubilized systems surfactant exchange

Thus far only processes involving motion of the surfactant as a whole have been mentioned. Other processes may occur in micellar solutions internal motion of the surfactant alkyl chains within the micelles exchange of cormterions between free and micelle-bound states and fast changes of micelle shape, among others. Also in the case of solubilized systems, i.e., micellar solutions that have solubilized compounds that are sparingly soluble in water, the solubilizate may exchange between micelles and the intermicellar solution. The dynamics of the exchange of counterions and of solubilizates are reviewed later. The dynamics of internal motions of the surfactant alkyl chains are not dealt with in this chapter, but some information and references can be found in Chapter 5, Section V. Some information on the fluctuations of micelle shapes can be found in Chapter 1, Section III.B. 

The chapter is organized as follows. Section II briefly recalls the theoretical aspects of micellar dynamics and the expressions of the relaxation times characterizing the main relaxation processes (surfactant exchange, micelle formation/breakdown). Section III reviews studies of micellar kinetics of various types of surfactants conventional surfactants with a hydrocarbon chain, surfactants with a fluorinated chain, and gemini (dimeric) surfactants. Section IV deals with mixed micellar solutions. Section V considers the d5mamics of solubilized systems. Section VI reviews the dynamics of sur-... 

Solubilized systems refer to surfactant solutions in which the micelles have solubilized compounds (solubilizates) that are generally poorly soluble in water. Most studies address the rate constants for the exchange of the solubilizate. A few studies examine the effect of solubilizate other than cosrufac-tants on the surfactant exchange and micelle forma-tion/breakdown. 

The book first discusses. self-assembling processes taking place in aqueous surfactant solutions and the dynamic character of surfactant self-assemblies. The next chapter reviews methods that permit the. study of the dynamics of self-assemblies. The dynamics of micelles of surfactants and block copolymers,. solubilized systems, microemulsions, vesicles, and lyotropic liquid crystals/mesophases are reviewed. successively. The authors point out the similarities and differences in the behavior of the.se different self-as.semblies. Much emphasis is put on the processes of surfactant exchange and of micelle formation/breakdown that determine the surfactant residence time in micelles, and the micelle lifetime. The la.st three chapters cover topics for which the dynamics of. surfactant self-assemblies can be important for a better understanding of observed behaviors dynamics of surfactant adsorption on surfaces, rheology of viscoelastic surfactant solutions, and kinetics of chemical reactions performed in surfactant self-assemblies used as microreactors. 

These are stable micelles that are formed with polymeric surfactants. Amphiphilic block copolymers such as the pluronics (polyoxyethylene-polyoxypropylene block copolymers) are able to self-assemble into polymeric micelles and hydrophobic drugs may be solubilized within the core of the micelle or, alternatively, conjugated to the micelle-forming polymer. Although micelles are rather dynamic systems that continuously exchange units between the micelle structure and the free units in solution, those composed of polyoxyethylene - poly(aspartic acid) have been found sufficiently... 

To overcome most of solubilization problems, colloidal surfactant systems (e.g. micelles, liquid crystals, microemulsions, vesicles, emulsions, etc.) are attracting a great deal of attention as alternative reaction media (Walde 1996 Holmberg 1997 Antonietti 2001). Their advantages are they possess micro- and nanostmctures consisting of well-defined hydrophilic and lipophilic domains separated by surfactant films with very large interfacial area, the exchange between chemical species... 

Micelles are dynamic structures where a rapid exchange of surfactant monomers takes place with bulk solution, with other micelles, and with surfactant molecules adsorbed on any solid surfece. Compounds solubilized by these systems participate in similar equilibria they exist in dynamic equilibrium with bulk solvent, micellar pseudo-phase, and any surface... 

The problem of solubilization in complex mixed fluids still remains open. Model mixed systems include surfactant solutions in the presence of inorganic two-dimensional objects such as clay, surfactants in the presence of linear polymers, and surfactants in the presence of globular nanoparticles, either inorganic or globular proteins. All of these model systems may be used to mimic solubilization in the environment. A general approach to this open problem is dealt with by Klumpp and Schwuger (59), who demonstrated that surfactants and multivalent ions are competitors for exchange at the surface of clays (as they should also be on humic acids). Once the mixed system is formed, the solubilization power (MAC) of the mixed surfactant system may be widely enhanced by reference to the separated surfactant and colloid. A spectacular example has been described... 

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