Molecular dynamics study on microstructures of diblock copolymer melts with soft potential and potential recovery.

Various microstructures are obtained through the self-assembly of block copolymers on the basis of the compositional fractions and repulsive interactions among different types of beads. The inhomogeneity of block copolymers can be studied by molecular dynamics. However, preparing initial configurations of various self-assembled structures directly by molecular dynamics requires extensive computational time because of topological constraints. Furthermore, manual preparation often becomes a complicated and time-consuming procedure even for the simplest structures, such as a lamellar phase, not to mention three-dimensional bicontinuous cubic phases such as a gyroid phase. In this paper, this difficulty is overcome by using a soft potential, which allows the system to reach a self-assembled state quickly (within 3τ_{d}). Once a self-assembled microstructure is obtained, the normal potential is restored and equilibration steps are performed to enable the calculation of various properties of the microstructures. Various equilibrated phase structures-including S (spherical), H (hexagonal), G (gyroid), and L (lamellar) phases-are obtained by this approach. To verify our method, static and dynamic properties of the lamellar phase are examined and compared with previous results.