Phase behavior of symmetric diblock copolymers under 3D soft confinement

TL;DR

This study explores how symmetric diblock copolymers self-assemble under 3D soft confinement, revealing diverse structures influenced by confinement degree and homopolymer selectivity, with implications for material design.

Contribution

It provides a comprehensive analysis of the phase behavior of diblock copolymers under soft 3D confinement, highlighting novel morphologies and transformation mechanisms.

Findings

Stacked lamellae form with neutral homopolymers, transitioning from Janus particles.

Non-lamellar morphologies emerge with selective homopolymers, including onion- and ring-like structures.

Reversible first-order transition between lamellae and onion structures based on homopolymer selectivity.

Abstract

The phase behavior of symmetric diblock copolymers under three-dimensional (3D) soft confinement is investigated using the self-consistent field theory. The soft confinement is realized in binary blends composed AB diblock copolymers and C homopolymers, where the copolymers self-assemble to form a droplet embedded in the homopolymer matrix. The phase behavior of the confined block copolymers is regulated by the degree of confinement and the selectivity of the homopolymers, resulting in a rich variety of novel structures. When the C homopolymers are neutral to the A- and B-blocks, stacked lamellae (SL) are formed where the number of layers increases with the droplet volume, resulting in a morphological transition sequence from Janus particle to square SL. When the C homopolymers are strongly selective to the B-blocks, a series of non-lamellar morphologies, including onion-, hamburger-, cross-, ring-, and cookie-like structures, are observed. A detailed free energy analysis reveals a first-order reversible transformation between SL and onion-like (OL) structures when the selectivity of the homopolymers is changed. Our results provide a comprehensive understanding of how various factors, such as the copolymer concentration, homopolymer chain length, degree of confinement, homopolymer selectivity, affect the self-assembled structures of diblock copolymers under soft 3D confinement.