Interplay of Solvation and Size Effects Induced by the Counterions in Ionic Block Copolymers on the Basis of Hofmeister Series

Abstract

AbstractTwo ionic block copolymers with different lengths of hydrophilic segments, polystyrene‐b‐poly(quaternized 4‐vinylpyridine)/ethyl bromide, are prepared by sequential reactions. They are originally self‐assembled into so‐called “large compound micelles” in aqueous solution. After ion exchange of Iˉ, SCN,ˉ and PF6ˉ for Brˉ, morphological transitions are controlled by a competition of solvation and size effects of the newly introduced counterions. The solvation effect is dominated in a relatively short corona‐forming block. Thus, sphere‐to‐wormlike particles, sphere‐to‐vesicle, and sphere‐to‐precipitate transitions are observed. In contrast, due to a long corona‐forming block, size effects become more profound after adding SCNˉ, thereby no morphological transition occurs. A morphological transition is characterized after partial exchange of Iˉ for Brˉ for both diblocks. A sphere‐to‐wormlike particles transition is observed only after most Brˉ is replaced by Iˉ. This work extends the understanding of morphological regulation through simple ion exchange and encourages rational design of nano‐assemblies.