Structural changes of diblock copolymer melts due to an external electric field: a self-consistent field theory study

摘要

We study the phase behavior of diblock copolymers in presence of an externalelectric field. We employ self-consistent field theory and treat the relevantMaxwell equation as an additional self-consistent equation. Because we do nottreat the electric field perturbatively, we can examine its effects even whenits magnitude is large. The electric field couples to the system's morphologyonly through the difference between the dielectric constants of the two blocks.We find that an external field aligns a body-centered cubic phase along the(111) direction, reducing its symmetry group to $R{\bar 3}m$. Transitionsbetween this phase and the disordered or hexagonal phases can occur forexternal electric fields ranging from a minimum to a maximum value beyond whichthe $R{\bar 3m}$ phase disappears completely. This electric-field range dependson diblock architecture and temperature. We present several cuts through thephase diagram in the space of temperature, architecture and applied field,including one applicable to a system recently studied.