Effects of a Nanophase-Separated Structure on Mechanical Properties and Proton Conductivity of Acid-Infiltrated Block Polymer Electrolyte Membranes under Non-Humidification

[Image: see text] Acid-infiltrated block polymer electrolyte membranes adopting a spherical or lamellar nanophase-separated structure were prepared by infiltrating sulfuric acid (H(2)SO(4)) into polystyrene-b-poly(4-vinylpyridine)-b-polystyrene (S–P–S) triblock copolymers to investigate the effects of its nanophase-separated structure on mechanical properties and proton conductivities under non-humidification. Lamellae-forming S–P–S/H(2)SO(4) membranes with a continuous hard phase generally exhibited higher tensile strength than sphere-forming S–P–S/H(2)SO(4) membranes with a discontinuous hard phase even if the same amount of Sa was infiltrated into each neat S–P–S film. Meanwhile, the conductivities of lamellae-forming S–P–S/H(2)SO(4) membranes under non-humidification were comparable or superior to those of sphere-forming S–P–S/H(2)SO(4) membranes, even though they were infiltrated by the same weight fraction of H(2)SO(4). This result is attributed to the conductivities of S–P–S/H(2)SO(4) membranes being greatly influenced by the acid/base stoichiometry associated with acid–base complex formation rather than the nanophase-separated structure adopted in the membranes. Namely, there are more free H(2)SO(4) moieties that can release free protons contributing to the conductivity in lamellae-forming S–P–S/H(2)SO(4) membranes than sphere-forming S–P–S/H(2)SO(4), even when the same amount of H(2)SO(4) was infiltrated into the S–P–S.