Dynamics of micro- and macrophase separation of amphiphilic block-copolymers in aqueous solution

The dynamics of purified poly(ethylene oxide)-block-poly(propylene oxide)-bloch-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.