Supracolloidal chains of patchy micelles in water

Abstract

Block copolymers have shown the potential to self-assemble into a rich variety of nanostructures with well-defined shapes and functions. Linear ABC triblock terpolymers are the first polymer architecture to allow the sequential collapse of polymer blocks and thus the formation of patchy micelles qualifying for hierarchical self-assembly into complex superstructures. Although solution self-assembly has become progressively more sophisticated, the controlled hierarchical structuring of linear triblock terpolymers in aqueous solution still remains challenging. Here, we show the synthesis and self-assembly of a bishydrophilic, pH-responsive triblock terpolymer into discrete patchy micelles followed by the hierarchical assembly into supracolloidal chains in water. The polymer features a water-soluble non-ionic polyethylene oxide (PEO) corona block, a hydrophobic polystyrene (PS) core block, and a poly(2-vinylpyridine) (P2VP) block able to switch from corona to core depending on pH. Using solvent sequences, we first form micelles with a PS core and a mixed PEO/P2VP corona. The P2VP block length was thereby chosen to be smaller than that of PS to give a large fraction of micelles with VSV core symmetry and to direct aggregation into linear supracolloidal chains of (VSV)_n. We analyze these supracolloidal chains under various preparation conditions to identify the most suitable path for extended growth. The results foster our understanding of the subtleties involved in the aqueous self-assembly of linear high molecular weight block copolymers and may in the future support the hierarchical self-assembly of linear multiblock and sequence-edited copolymers.