Morphological Changes in Block Copolymer Melts Due to a Variation of Intramolecular Branching. Dissipative Particles Dynamics Study

Abstract

We performed dissipative particles dynamics (DPD) simulations for the melts of various star and comb diblock copolymers with equal molecular weight (L = 41 beads) but with various types of internal branching. To assist formation of native morphologies, an anisotropic NPT ensemble was used. For the linear diblock polymer, we reevaluated the phase diagram in a high segregation regime and confirmed existence of the gyroid phase. The equilibrium morphologies and molecular conformations of branched molecules are compared with those found in the linear diblock copolymers at the same composition fraction. The analysis of the morphologies is performed in terms of metrics, spacial arrangement, and conformations of the molecules. Both weak (no phase change) and strong (phase changes) branching effects are observed. Promotion of a less ordered phase occurs in the case when highly constrained beads are unable to fill in required space regions (defined by the phase pitch) homogeneously. As a result, more ordered phase (observed for the linear diblock) cannot be formed. In some cases, an opposite effect is observed, e.g., promotion of more ordered lamellar phase (in place of the hexagonal one for the linear diblock) by suitable symmetry of the comb architecture.