Formation of rodlike block copolymer micelles in aqueous salt solutions

SANS measurements have been performed on the water-soluble PEO-PPO-PEO triblock copolymer P85 [(EO)26(PO)39(EO)26] in the presence of salts KCl, KF and K2CO3 in aqueous solution. Addition of these salts entropically favours dehydration from the micelles (similar to that of increasing temperature) and this leads to the formation of rodlike block copolymer micelles at ambient temperature. The rodlike micelles coexist with spherical micelles at higher salt concentrations or temperatures in these systems even up to the onset of phase separation. The hydration properties of the salt anions determine the population of the rodlike micelles.