Shape transition in ABC triblock copolymer micelles complexed with SDS through quaternized polyvinyl pyridine central block

Polystyrene-b-poly-2-vinylpridine-b-polyethyleneoxide (PS₁₃-PVPy₆₂-PEG₄₇) block copolymer forms spherical core-shell-corona micelles (~50 nm) in water. At acidic pH~3, the central PVPy block gets quaternized (hydrophilic) and gets complexed with sodium dodecyl sulfate (SDS), which strongly interacts with PVPy⁺ electrostatically as reflected from marked increase in turbidity. The charge neutralization of the central block and accordingly favored hydrophobicity induces interesting structural transitions. Cryo-TEM images for micellar solution of block copolymer in the presence of 10 mM SDS at pH~3 show presence of micelles of ribbon type and threadlike morphology. SANS measurements support the micelle growth and shape transition for the block copolymer aggregates as fitted by core-shell model.