On the kinetics of Micellization, Measured with Pressure‐Jump and Stopped‐Flow

Abstract

In relaxation experiments in aqueous micellar solutions one observes two processes. In order to compare the kinetic data obtained by different methods, these processes were investigated using p‐jump and stopped‐flow as perturbation methods, and conductivity and extinction as detection methods. The agreement is sufficient. — The results for the amplitudes measured in stopped‐flow experiments indicate, that with ionic surfactants the number density of monomers does not remain constant above the cmc, but decreases again with increasing surfactant concentration. The consideration of this fact leads to a qualitative agreement between theory and experiment.

Dynamics of Block Copolymer Micelles in Aqueous Solution

“…The amplitude of this process would simply go from negative to positive at a temperature corresponding to that at about midrange of the gap between T 1 and T 1 + 4, as is suggested by the results in Figure B. At this stage we recall that the relaxation amplitude for the micelle formation−breakup process has been reported to change sign for several micellar systems based on conventional surfactants. −

1 (A) Temperature dependence of the relaxation times τ 2 and τ 3 for aqueous solutions of 2.5% (w/v) purified L64 (▪, ▴), 2.5% (w/v) industrial L64 (□, ▵) and a mixture of 2.5% w/v purified L64 and 0.25% w/v L61 (+, ◇). (B).

…”

“…At this stage we recall that the relaxation amplitude for the micelle formation-breakup process has been reported to change sign for several micellar systems based on conventional surfactants. [11][12][13] It may be argued that the processes characterized by τ 2 and τ 3 were also detected by stopped-flow. 6,7 However, these experiments were performed in conditions very different from those by T-jump.…”

Formation Kinetics of Oil-Rich, Nonionic Microemulsions

“…Employing a larger amount of surfactantand thereby covering the complete interface between polar and nonpolar substancethermodynamically stable, nanostructured microemulsions may form. − Although their equilibrium properties like phase behavior, − low oil/water interfacial tension, , and multifarious nanostructure − have been studied in great detail for the past quarter of a century, far less is known about their formation kinetics and the formation of the internal interface in particular. In older related studies the pressure- and temperature-induced micelle formation was investigated in (pseudo)­binary water/surfactant mixtures − as well as the transformation of spherical micelles to elongated ones. , For these transitions similar studies have also been conducted using block copolymers. − Beyond that, most of the other related experiments deal with the kinetics of structural transformations, e.g., the well-studied micelle-to-vesicle transition ,− induced mainly by changes in the composition (using the stopped-flow technique) − or the lamellar-to-sponge (L 3 ) transition due to changes in temperature or pressure . Kinetic experiments on microemulsions concentrate on the exchange kinetics of prestructured inverse w/o microemulsions − or most recently on the pressure-induced sphere-to-cylinder transitions of CO 2 -swollen micelles .…”

Kinetics of pressure induced structural changes in super- or near-critical CO2-microemulsions

“…CO 2 -microemulsions represent promising model systems, since the density of CO 2 and thus its solvent properties 21,22 are strongly influenced by varying pressure. Besides older studies on the micelle kinetics 23,24 or on inverse w/o-microemulsions, 25,26 previous kinetics studies concentrated on the micelle-to-vesicle transition induced mainly by changes in the composition (using the stopped-flow technique) [27][28][29] or the lamellar (L a )-to-sponge (L 3 ) transition due to changes in the temperature or pressure. 30,31 For interpretation of the kinetics, the static properties of the CO 2 -microemulsions have to be known.…”