Spontaneous Origination of Chirality in Melts of Diblock Copolymers with Rigid and Flexible Blocks

A self-consistent mean-field computer simulation of ordering in melts of diblock copolymers consisting of flexible and rigid rodlike blocks is performed. A three-dimensional model is considered, and a corresponding algorithm for solving mean-field equations in sequential and parallelized versions is developed. The coexistence of microphase separation and orientational ordering gives rise to the appearance of new types of spatial arrangements. In particular, phases with the cubic symmetry and the morphology of hexagonally arranged chiral cylinders are found. The transition of achiral cylinders to chiral cylinders in the melt of achiral diblock copolymers consisting of rigid and flexible blocks is revealed for the first time. The origination of chirality is due to the presence of rigid blocks in the system and orientational interactions between them. With a decrease in temperature, microphase separation caused by incompatibility of chemically different blocks initially occurs in these systems. As a result, the hexagonally ordered structure in which rigid blocks are concentrated in cylindrical microdomains arises. A further decrease in temperature results in the involution of cylindrical microdomains and the formation of a helical structure. To quantify the degree of chirality, a new pseudoscalar index, depending on the linear-scale parameter for which the chirality is studied, is suggested.