Surfactant micelle dynamics formation/breakdown

As mentioned above, the most important adjuvants are surface active agents of the anionic, nonionic or zwitterionic type. In some cases polymers are added as stickers or antidrift agents. The production of spray droplets (from a spray nozzle) is determined by the adsorption of surfactants under dynamic conditions (with time in the region of 1 ms). The droplet adhesion to the target surface and its wetting and spreading is also determined by the dynamic contact angle which is also determined by the rate of surfactant adsorption to the surfeice. Above the critical micelle concentration (cmc), the supply of monomers is determined by the relaxation time of micelle formation and its breakdown. The dynamics of surfactant adsorption is determined by the monomer concentration and the diffusion coefftcient of the surfactant molecules to the interface. 

Besides, micelles are dynamic objects. They constantly exchange surfactant with the bulk phase exchange process), and they form and break down by different pathways micelle formation / breakdown), which are reviewed in Chapter 3. 

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-... 

The effect of alcohol on the dynamic properties of micellar systems has been considered as a first approach toward the understanding of microemulsion systems. In mixed alcohol + surfactant micelles, the theory predicts the existence of three relaxation processes, which have been experimentally observed using chemical relaxation techniques a slow process associated with the formation/breakdown of mixed micelles and two fast processes associated with the exchange of the surfactant and alcohol, respectively, between the mixed micelles and the bulk aqueous phase. With g representing a mixed micelle with a alcohol (A) molecules and s surfactant (S) molecules, these two exchange reactions can be written in the form... 

The study of vesicle dynamics is now a mature area of research. The main processes involved in bilayer mobility and solute transport are quite well vmderstood, but this is not so with the spontaneous formation and breakdown of vesicles. There is a significant difference between the d5mamics of micelle forma-tion/breakdown and vesicle formation/breakdown. Micelle phenomena occur on a very short time scale, with processes for most micellar systems taking place in time scales less than 1 sec. For vesicles of synthetic surfactants like the alkylbenzene-sulfonates, the relevant processes are in the second to minute time range, although surfactant monomer exchange between vesicles and aqueous solution may well take place in the mil-... 

Dynamics of Surfactant Self-Assemblies explains the dynamics of micellar equilibria, tracking surfactant exchange, and micelle formation/breakdown processes. Highlighting the structural similarities of amphiphilic block copolymers to surfactants, this volume elucidates the dynamics of more complex self-as.semblies that surfactants and amphiphilic block copolymers form in solutions. 

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. 

The dynamics of micellar equilibria — that is, of surfactant exchange and micelle formation/breakdown processes — have been investigated a great deal. Indeed, in addition to providing a better knowledge of micellar systems, a good understanding of the dynamics of micelles is required for the interpretation of experimental results obtained in other areas of surfactant science. The most... 

So far, all of the studies detailed have dealt primarily with nonequilibrium states, i.e micelle formation or breakdown stimulated by an external trigger, e.g., a jump in pressure, temperature, or concentration. It has of course been shown, however, that even at equilibrium, micelles are by their nature transient species with millisecond-scale lifetimes, and that dynamic processes exchange surfactant molecules between aggregates, interfaces, and bulk solutions. Studies of the kinetics of these processes in equilibrium solutions are much more scarce, mainly owing to experimental difficulties. 

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