Formation of rodlike block copolymer micelles in aqueous salt solutions

Abstract

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