Helix formation via kinetic assembly of charged block copolymer cylinders in solution

A multi-micrometer-long, cylinder with helical superstructure is created from coassembly of poly(acrylic acid)-\textit{block}-poly(methyl acrylate)-\textit{block}-polystyrene (PAA-$b$-PMA-$b$-PS) triblock copolymers with excessive triethylenetetramine or diethylenetriamine in the mixture of 67{\%} volume ratio of water in tetrahydrofuran (THF). The stable pitch distance of the formed helices is due to the balance of long range electrostatic association and uniaxial tension along the cylinder, which can be efficiently tuned by varying the type and amount of the multivalent amine molecules. Double and triple helices are also formed with characteristic interhelical cynlinder distances similar to what is observed as the pitch in single helices. A kinetic study shows that the formation of a helix undergoes a complex, but reproducible, nanostructure evolution, including a starting stacked structure, a transition state of very short helices with the length of tens of nanometers and a final multi-micrometer-long mature helix by connecting those short helices.