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

TL;DR

This study uses self-consistent field theory to analyze how external electric fields influence the phase behavior and morphology of diblock copolymer melts, revealing field-induced phase alignments and transitions.

Contribution

It introduces a non-perturbative self-consistent approach to examine electric field effects on diblock copolymers, accounting for large field magnitudes and dielectric contrasts.

Findings

Electric field aligns bcc phase along (111) direction

Transitions occur between ordered and disordered phases under varying fields

Phase diagrams depend on temperature, architecture, and field strength

Abstract

We study the phase behavior of diblock copolymers in presence of an external electric field. We employ self-consistent field theory and treat the relevant Maxwell equation as an additional self-consistent equation. Because we do not treat the electric field perturbatively, we can examine its effects even when its magnitude is large. The electric field couples to the system's morphology only 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 $R{\bar 3}m$. Transitions between this phase and the disordered or hexagonal phases can occur for external electric fields ranging from a minimum to a maximum value beyond which the $R{\bar 3m}$ phase disappears completely. This electric-field range depends on diblock architecture and temperature. We present several cuts through the phase diagram in the space of temperature, architecture and applied field, including one applicable to a system recently studied.