Zwitterion-Stabilized Superlattices and Frank-Kasper Phases in Charged Block Copolymers for Mechanically Robust...

Superlattice structures, created by the periodic arrangement of two or more distinct materials, have attracted significant interest. This paper proposes a strategy for designing superlattice structures in soft materials with improved dielectric and mechanical properties. Two types of acid-functionalized block copolymers and a series of zwitterions with varying cationic and anionic structures are synthesized. When the zwitterion anion possesses a localized charge and the cation exhibits weak interactions with the acid groups in the polymers, the zwitterions preferentially localize at the interfacial layers between the ionic and ionophobic domains. As the zwitterion concentration increases and ion-dipole interactions strengthen within the confined subdomains, the interfacial curvature of the superlattice transitions from lamellae to cylindrical morphology and further evolves to Frank-Kasper phases. Notably, these morphological transitions occur despite the symmetrical volume fractions of the ionic phases. These superlattice structures and Frank-Kasper phases exhibit thermal stability up to 150 °C, a high static dielectric constant of 25, and excellent mechanical properties including a modulus of 360 MPa, hardness of 16 MPa, stiffness of 772 N m^-1, and energy dissipation index of 0.675 at 22 °C, making them highly promising candidates for advanced applications in soft electronics and memory devices.