Influence of substrate interaction and confinement on electric field induced transition in symmetric block copolymer thin films

TL;DR

This study investigates how substrate interaction, electric fields, and confinement influence the morphology of symmetric diblock copolymer thin films using a coupled electrostatic and phase separation model, revealing complex phase behavior.

Contribution

It introduces a coupled Ohta-Kawasaki and Maxwell equation model that captures hybrid morphologies and phase transitions without approximations, advancing understanding of copolymer behavior under external stimuli.

Findings

Identification of parallel, perpendicular, and mixed lamellae phases.

Discovery of hybrid morphologies due to substrate and electric field effects.

Dependence of phase transition fields on substrate strength, film thickness, and dielectric contrast.

Abstract

In the present work, we study morphologies arising due to competing substrate interaction, electric field and confinement effects on a symmetric diblock copolymer. We employ a coarse grained non-local Cahn-Hilliard phenomenological model taking into account the appropriate contributions of substrate interaction and electrostatic field. The proposed model couples the Ohta-Kawasaki functional with Maxwell equation of electrostatics, thus alleviating the need for any approximate solution used in previous studies. We calculate the phase diagram in electric field-substrate strength space for different film thicknesses. In addition to identifying the presence of parallel, perpendicular and mixed lamellae phases similar to analytical calculations, we also find a region in the phase diagram where hybrid morphologies (combination of two phases) coexist. These hybrid morphologies arise either solely due to substrate affinity and confinement or are induced due to the applied electric field. The dependence of the critical fields for transition between the various phases on substrate strength, film thickness and dielectric contrast is discussed. Some preliminary 3D results are also presented to corroborate the presence of hybrid morphologies.