Emergence and Stability of a Hybrid Lamella–Sphere Structure from Linear ABAB Tetrablock Copolymers

Abstract

The self-assembly of linear A 1 B 1 A 2 B 2 tetrablock copolymers is studied using the self-consistent field theory, aiming to target the formation of stable hybrid structures composed of lamellar and spherical domains of the same component, i.e., the lamella–sphere (LS) phase. Two types of lamellar morphologies, regular (L) and sandwich-like (L′), are observed, and their transition is identified as first-order. The formation of L′ is a prior condition for the formation of LS because the disordered short A 2 -blocks sandwiched in the B domain in L′ aggregate into spheres as χ N increases, leading to the formation of LS. The separation of A 2 -blocks from A 1 -blocks in L′ or LS causes extra interfacial energy, which is compensated by the gain of configurational entropy. The tail B 2 -block is demonstrated to play a critical role in enlarging the gain of configurational entropy. In a word, the formation of L′ is driven by entropy, while the transition from L′ to LS is driven by enthalpy.