The dynamics of purified poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO−PPO−PEO) block-copolymer micellization and phase separation in aqueous solutions were studied using the iodine laser temperature-jump and stopped flow techniques. The changes in the micellar solutions were followed by either light scattering or fluorescence of 1,6-diphenyl-1,3,5-hexatriene (DPH), which is a probe located in the micelle interior. Three different relaxation processes were observed for the temperature range covering the micro- and macrophase separation of the EO13PO30EO13 (Pluronic L64) block-copolymer. The fastest process corresponds to the incorporation of unimers into micelles which leads to larger micelles that are not thermodynamically stable. This process is followed by a relaxation with negative amplitude during which the micellar core is dehydrated and a redistribution of micellar sizes is achieved. The third relaxation process corresponds to the clustering of micelles into larger aggregates which is associated with the initial step of macrophase separation. Other PEO−PPO−PEO block-copolymers, like EO19PO43EO19 (Pluronic P84) and EO27PO61EO27 (Pluronic P104), were investigated to provide additional information concerning the second relaxation process. Mixed micelles containing sodium dodecyl sulfate were studied to support the assignment of relaxation processes involving micellar collisions. This study of the dynamics of purified PEO−PPO−PEO block-copolymers clarifies several controversial points because the dynamics were investigated over a wide temperature and concentration range and avoid impurity effects.

The dynamics of the micellization of Pluronic® L64 (EO13PO30EO13, PEO/PPO = 2/3) was studied by employing the iodine laser temperature-jump technique. These studies show a more complex behavior than previously described. Three relaxation processes were observed, depending on the temperature at which experiments were performed. The first two of these relaxation processes are related to the unimer incorporation into micelles and the redistribution of micelles after incorporation of the unimers. The third relaxation process, which had not been previously observed, occurs at high temperatures and is related to the clustering of micelles into larger aggregates. In addition, the presence of impurities and hydrophobic components was shown for the first time to significantly affect the dynamics of L64 micellization.

No abstract