Pressure jump micellar systems

The kinetics of formation and disintegration of micelles has been studied for about thirty years [106-130] mainly by means of special experimental methods, which have been proposed for investigation of fast chemical reaction in liquids [131]. Most of the experimental methods for micellar solutions study the relaxation of small perturbations of the aggregation equilibrium in the system. Small perturbations of the micellar concentration can be generated by either fast mixing of two solutions when one of them does not contain micelles (method of stopped flow [112]), or by a sudden shift of the equilibrium by instantaneous changes of the temperature (temperature jump method [108, 124, 129, 130]) or pressure (pressure jump method [1, 107, 116, 122, 126]). The shift of the equilibrium can be induced also by periodic compressions or expansions of a liquid element caused by ultrasound (methods of ultrasound spectrometry [109-111, 121, 125, 127]). All experimental techniques can be described by the term relaxation spectrometry [132] and are characterised by small deviations from equilibrium. Therefore, linearised equations can be used to describe various processes in the system. 

Lang et al. [80] were one of the early teams who lent support to the development of the above idea while working with aqueous solutions of sodium lauryl sulfate and laurylpyridinium chloride, bromide and iodide (CMC known in each case), and dissolved salts. They noticed two relaxation processes in the above micellar systems by examination through ultrasonic absorption, pressure jump, temperature jump and shock tube measurements. The two relaxation processes, one relatively fast and the other slow, were dependent on the... 

Rassing et al. [62] studied kinetics of sodium perfluorooctanoate micellar systems using the ultrasonic relaxation method. They observed a fast relaxation process attributed to a micelle formation. The ultrasonic relaxation times revealed that periodic fluctuations in temperature and pressure caused by the acoustic wave are several magnitudes less than the temperature or pressure perturbations of jump techniques. Rassing et al. [62] suggested that the ultrasonic and jump methods measure different modes of micelle formation whose relaxation times differ by several orders of magnitude. Ultrasonic absorption techniques [69-71 ] have also been used to measure relaxation spectra of sodium perfluorooctanoate and cesium perfluorooctanoate [72,73]. 

The kinetics of micellization of perfluorinated surfactants has been investigated by Hoffmann and co-workers [74-80] by pressure jump and a shock wave method with conductivity detection [74-80]. Hoffmann and Ulbricht [75] also used a temperature jump relaxation technique [81] with optical detection, utilizing a pH indicator (thymol blue) to observe relaxation processes of a 1 1 mixture of perfluorooctanoic acid and its sodium salt. For micellar systems in which fast relaxation times could be measured, the parameters k /n, k lcr, a ln, and k /n were calculated. 

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