Hydration-Dependent Hierarchical Structures in Block Copolymer–Surfactant Complex Salts

Block copolymer–surfactant “complex salts” (BCPCS), containing one neutral water-soluble block and one polyion/surfactant-ion block, were prepared from poly(acrylamide)-block-poly(acrylic acid) block copolymers by neutralizing the acrylate charges with cationic dodecyl- or hexadecyltrimethylammonium surfactant counterions. The BCPCS were studied in hydrated samples containing 20–99 wt % water (and no additional ions) employing small-angle X-ray scattering (SAXS), dynamic light scattering (DLS), and visual inspection. Selected samples in D2O were also investigated. The results reveal for the first time, for hydrated samples, the formation of ordered hierarchical structures on both block copolymer and surfactant length scales, analogous to structures that have previously been reported for solvent-free block copolymer–surfactant complexes in the solid or melt. The BCPCS structures do not dissolve but display a finite swelling also in the presence of excess water. The structure on the BCP length scale (lamell...