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

The dynamics of purified poly(ethylene oxide)-block-poly(propylene oxide)-b loch-poly(ethylene oxide) (PEO-PPO-PEO) block-copolymer micellization and p hase separation in aqueous solutions were studied using the iodine laser te mperature-jump and stopped flow techniques. The changes in the micellar sol utions were followed by either light scattering or fluorescence of 1,6-diph enyl-1,3,5-hexatriene (DPH), which is a probe located in the micelle interi or. Three different relaxation processes were observed for the temperature range covering the micro- and macrophase separation of the EO13PO30EO13 (Pl uronic L64) block-copolymer. The fastest process corresponds to the incorpo ration of unimers into micelles which leads to larger micelles that are not thermodynamically stable. This process is followed by a relaxation with ne gative amplitude during which the micellar core is dehydrated and a redistr ibution of micellar sizes is achieved. The third relaxation process corresp onds to the clustering of micelles into larger aggregates which is associat ed with the initial step of macrophase separation. Other PEO-PPO-PEO block- copolymers, like EO19PO43EO19 (Pluronic P84) and EO27PO61EO27 (Pluronic P10 4), were investigated to provide additional information concerning the seco nd relaxation process. Mixed micelles containing sodium dodecyl sulfate wer e studied to support the assignment of relaxation processes involving micel lar collisions. This study of the dynamics of purified PEO-PPO-PEO block-co polymers clarifies several controversial points because the dynamics were i nvestigated over a wide temperature and concentration range and avoid impur ity effects.