Defects in Lamellar Diblock Copolymers: Chevron- and Omega-shaped Tilt Boundaries

TL;DR

This paper studies the structure of tilt boundaries in lamellar diblock copolymers, revealing how interface morphology changes with grain boundary angle and providing a theoretical model that matches experimental and numerical results.

Contribution

It introduces a Ginzburg-Landau based theoretical approach to analyze tilt boundaries in lamellar diblock copolymers, connecting morphology with boundary angle.

Findings

Chevron morphology occurs at small angles.

Omega morphology appears at larger angles.

Theoretical results agree with experiments and numerical simulations.

Abstract

We investigate symmetric grain boundaries in a lamellar diblock copolymer system. The form of the interface between two grains strongly depends on the angle $\theta$, between the normals of the grains. When this angle is small, the lamellae transform smoothly from one orientation to the other, creating the chevron morphology. As $\theta$ increases, a gradual transition is observed to an omega morphology characterized by a protrusion of the lamellae along the interface between the two phases. We present a theoretical approach to find these tilt boundaries in two-dimensional systems, based on a Ginzburg-Landau expansion of the free energy. Calculated order parameter profiles and energies agree well with transmission electron microscope experiments, and with full numerical solution of the same problem.