Origin of polytypism in block copolymer materials

Abstract

Block copolymers have served as versatile model compounds to understand the self-assembly of inhomogeneous materials. However, the close-packed structures and relevant polytypic crystal systems in block copolymer materials still require a better understanding. In this research update, we review early and recent advancements in close-packed structures in block copolymer materials and attempts to present a framework to understand the origin of polytypism in polymeric and relevant systems. We propose a critical role of interstitial space as a structure director in polytypism and introduce the interstitial space distribution factor as a semiquantitative parameter to address the difference in the configurations of interstitial space distribution in polytypes of the same class. We also note that the random stacking of two-dimensional close-packed structures is a class of aperiodic crystals.