Structural Hierarchy in Flow-Aligned Hexagonally Self-Organized Microphases with Parallel Polyelectrolytic Structures

We report a novel structural hierarchy where a flow-aligned hexagonal self-organized structure is combined with a polyelectrolytic self-organization on a smaller length scale and where the two structures are mutually parallel. Polystyrene-block-poly(4-vinylpyridine) (PS-block-P4VP) is selected with a short P4VP block, which is protonated with p-toluenesulfonic acid (TSA) and further hydrogen bonded with 3-n-pentadecylphenol (PDP). To suppress the amount of free (uncomplexed) acid which we expected to have adverse effects during the extended shearing at the elevated temperatures, a safely less than stoichiometric amount of TSA was used, i.e., PS-block-P4VP(TSA)0.9(PDP)1.0. The formation of the supramolecules and the resulting structures were investigated using infrared spectroscopy (FTIR), small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM). As the weight fraction of P4VP(TSA)0.9(PDP)1.0 is ca. 20%, hexagonal self-organization occurs, as shown by SAXS. Shear flow leads to remarkably well-aligned structures. SAXS also indicates an internal structure within the P4VP(TSA)0.9(PDP)1.0 blocks with a long period of 41 Å. In contrast to the previously observed structural hierarchies in diblock copolymer/amphiphile supramolecules, which contained mutually perpendicular structures, e.g., lamellae within cylinders, in the present case SAXS in combination with models suggests internal polyelectrolytic layers parallel to the hexagonally ordered microphases. These aligned conducting nanochannels also manifest as a slight overall conductivity anisotropy.