Pattern formation mechanisms in sphere-forming diblock copolymer thin films

TL;DR

This study numerically investigates the mechanisms of pattern formation in sphere-forming diblock copolymer thin films, highlighting the roles of spinodal decomposition and nucleation, and comparing results with experimental observations.

Contribution

It provides a detailed numerical analysis of pattern formation mechanisms in diblock copolymer thin films, emphasizing the conditions influencing spinodal and nucleation processes.

Findings

Pattern formation occurs via spinodal decomposition and nucleation.

The validity range of each process depends on temperature relative to transition points.

Numerical results align qualitatively with experimental data.

Abstract

The order-disorder transition of a sphere-forming block copolymer thin film was numerically studied through a Cahn-Hilliard model. Simulations show that the fundamental mechanisms of pattern formation are spinodal decomposition and nucleation and growth. The range of validity of each relaxation process is controlled by the spinodal and order-disorder temperatures. The initial stages of spinodal decomposition are well-approximated by a linear analysis of the evolution equation of the system. In the metastable region, the critical size for nucleation diverges upon approaching the order-disorder transition, and reduces to the size of a single domain as the spinodal is approached. Grain boundaries and topological defects inhibit the formation of superheated phases above the order-disorder temperature. The numerical results are in good qualitative agreement with experimental data on sphere-forming diblock copolymer thin films.