Epitaxial Transition from Gyroid to Cylinder in a Diblock Copolymer Melt

TL;DR

This study simulates the transition from a gyroid to a cylinder structure in diblock copolymer melts under shear flow, revealing epitaxial growth and reconnection processes with a novel system size optimization technique.

Contribution

It introduces a system size optimization method for accurate simulation of structural transitions in copolymer melts under flow conditions.

Findings

Epitaxial nucleation and growth of cylinders from gyroid under shear flow.

Different reconnection processes depend on shear flow direction.

The predicted intermediate junction states were not observed.

Abstract

An epitaxial transition from a bicontinious double gyroid to a hexagonally packed cylinder structure induced by an external flow is simulated using real-space dynamical self-consistent field technique. In order to simulate the structural change correctly, we introduce a system size optimization technique by which emergence of artificial intermediate structures are suppressed. When a shear flow in [111] direction of the gyroid unit cell is imposed, a nucleation and growth of the cylinder domains is observed. We confirm that the generated cylindrical domains grow epitaxially to the original gyroid domains as gyroid $d_{\{220\}}$ $\to$ cylinder $d_{\{10\}}$. In a steady state under the shear flow, the gyroid shows different reconnection processes depending on the direction of the velocity gradient of the shear flow. A kinetic pathway previously predicted using the self-consistent field theory where three fold junctions transform into five fold junctions as an intermediate state is not observed.