Symmetric Diblock Copolymers in Thin Films (I): Phase stability in Self-Consistent Field Calculations and Monte Carlo Simulations

TL;DR

This study examines the phase behavior of symmetric AB diblock copolymers in thin films, using self-consistent field theory and Monte Carlo simulations to analyze phase stability, transitions, and morphology depending on film thickness and incompatibility.

Contribution

It provides a comparative analysis of phase transitions and morphologies in thin films of diblock copolymers using both theoretical and simulation methods, highlighting agreement between approaches.

Findings

First order transitions between lamellae with different numbers of layers.

Transitions between parallel and perpendicular lamellae based on incompatibility and film thickness.

Good agreement between self-consistent field calculations and Monte Carlo simulations.

Abstract

We investigate the phase behavior of symmetric AB diblock copolymers confined into a thin film. The film boundaries are parallel, impenetrable and attract the A component of the diblock copolymer. Using a self-consistent field technique [M.W. Matsen, J.Chem.Phys. {\bf 106}, 7781 (1997)], we study the ordered phases as a function of incompatibility $\chi$ and film thickness in the framework of the Gaussian chain model. For large film thickness and small incompatibility, we find first order transitions between phases with different number of lamellae which are parallel oriented to the film boundaries. At high incompatibility or small film thickness, transitions between parallel oriented and perpendicular oriented lamellae occur. We compare the self-consistent field calculations to Monte Carlo simulations of the bond fluctuation model for chain length N=32. In the simulations we quench several systems from $\chi N=0$ to $\chi N=30$ and monitor the morphology into which the diblock copolymers assemble. Three film thicknesses are investigated, corresponding to parallel oriented lamellae with 2 and 4 interfaces and a perpendicular oriented morphology. Good agreement between self-consistent field calculations and Monte Carlo simulations is found.