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

摘要

Two 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 I~ˉ, SCN,~ˉ and PF6~ˉ for Br~ˉ, 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 SCN~ˉ, thereby no morphological transition occurs. A morphological transition is characterized after partial exchange of I~ˉ for Br~ˉ for both diblocks. A sphere-to-wormlike particles transition is observed only after most Br~ˉ is replaced by I~ˉ. This work extends the understanding of morphological regulation through simple ion exchange and encourages rational design of nano-assemblies.