Binary Blends of Diblock Copolymers: An Efficient Route to Complex Spherical Packing Phases

TL;DR

This study uses self-consistent field theory to explore how binary blends of diblock copolymers can be used to stabilize complex spherical packing phases, revealing new phase behaviors and segregation patterns.

Contribution

It demonstrates that binary blends of diblock copolymers can efficiently induce and control complex spherical packing phases, expanding the understanding of phase stability in such systems.

Findings

Complex phases like Frank-Kasper A15 and $\sigma$ can be stabilized.

Longer A$_2$B$_2$-copolymers promote complex phase formation.

Phase behaviors align with experimental and theoretical results.

Abstract

The phase behaviour of binary blends composed of A$_1$B$_1$ and A$_2$B$_2$ diblock copolymers is systematically studied using the polymeric self-consistent field theory, focusing on the formation and relative stability of various spherical packing phases. The results are summarized in a set of phase diagrams covering a large phase space of the system. Besides the commonly observed body-centered-cubic (BCC) phase, complex spherical packing phases including the Frank-Kasper A15 and $\sigma$ and the Laves C14 and C15 phases could be stabilized by the addition of longer A$_2$B$_2$-copolymers to asymmetric A$_1$B$_1$-copolymers. Stabilizing the complex spherical packing phases requires that the added A$_2$B$_2$-copolymers have a longer A-block and an overall chain length at least comparable to the host copolymer chains. A detailed analysis of the block distributions reveals the existence of inter- and intra-domain segregation of different copolymers, which depends sensitively on the copolymer length ratio and composition. The predicted phase behaviours of the A$_1$B$_1$/A$_2$B$_2$ diblock copolymer blends are in good agreement with available experimental and theoretical results. The study demonstrated that binary blends of diblock copolymers provide an efficient route to regulate the emergence and stability of complex spherical packing phases.