Self-assembly and flow alignment of protonically conducting complexes of polystyrene-block-poly(4-vinylpyridine) diblock copolymer with phosphoric acid

Phosphoric acid (H₃PO₄) is selectively swollen in polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymer within its P4VP domains to achieve protonically conducting self-assembled acid–base complexes. Shear flow is imposed to macroscopically align the local self-assembled structures. The materials are characterized using Fourier transformation infrared spectroscopy (FTIR), small angle X-ray scattering (SAXS), dynamic rheology, and impedance spectroscopy. Homopolymeric P4VP(H₃PO₄)_x (where x denotes the nominal number of H₃PO₄ molecules vs. repeat units of P4VP) reaches the conductivity value ca. 5 * 10^− 3 S/cm at 100 °C when x approaches the values x = 2.0 ⋯ 2.5. By incorporating a P4VP(H₃PO₄)_2.2 block within PS-block-P4VP (with the block lengths 35.5 and 3.6 kD for PS and P4VP, respectively; polydispersity 1.06), lamellar protonically conducting nanochannels are formed with periodicity of ca. 450 Å based on SAXS. Large-amplitude oscillatory shear flow is applied, which leads to macroscopically rather highly aligned lamellar nanochannels based on SAXS. Surprisingly, this leads to only slightly anisotropic conductivities. For example, at 100 °C conductivity of 5 * 10^− 6 S/cm along the channels and 7 * 10^− 7 S/cm in the perpendicular direction are obtained. The observations indicate that defects, potentially involving “dead-end channels” may control the transport properties in self-assembled and aligned materials across macroscopic dimensions.