Chirality in Self-Assembling Rod-Coil Copolymers: Macroscopic Homochirality Versus Local Chirality

Abstract

We study chiral mesophases arising as a result of the interplay between microphase separation and orientational ordering in diblock rod-coil copolymers. It is shown that nearly compositionally symmetric copolymers form a columnar structure with twisted rod-rich domains, whereas there is a suppression of the lamellar morphologies with respect to the columnar one. Using high-resolution three-dimensional self-consistent field simulations, we show that chirality in the unit cell of the hexagonal phase develops in two different ways, leading to either homochiral state or heterochiral (locally chiral) state. Thus, chiral polarization, which occurs when the rigid and flexible blocks are segregated, causes a transition to two degenerate chiral states. In a system with many twisted domains, the magnitude of the chirality charge obeys the binomial distribution with random selection of the twist direction for each of the rod-rich domains. We suggest a model of pseudodynamical structural evolution aimed at understanding of how chirality arises from the achiral state and how it evolves. At the initial stage of the evolutionary process, there exists some waiting time for the onset of irreversible changes in chirality; during this time the system flips between the two chirality states.