Controlling the self-assembly of binary copolymer mixtures in solution through molecular architecture

TL;DR

This study combines experiments and modeling to show how copolymer architecture influences self-assembly, enabling control over structures like vesicles and aggregates in binary PEO-PCL mixtures.

Contribution

It demonstrates how altering copolymer chain geometry and composition directs the formation of specific self-assembled nanostructures, supported by experimental and theoretical analysis.

Findings

Increasing lamella-former molecular weight promotes highly-curved structures.

Binary lamella-former mixtures form vesicles with intermediate wall thickness.

Sphere-former and large hydrophobic block copolymer mixtures produce novel elongated vesicles.

Abstract

We present a combined experimental and theoretical study on the role of copolymer architecture in the self-assembly of binary PEO-PCL mixtures in water-THF, and show that altering the chain geometry and composition of the copolymers can control the form of the self-assembled structures and lead to the formation of novel aggregates. First, using transmission electron microscopy and turbidity measurements, we study a mixture of sphere-forming and lamella-forming PEO-PCL copolymers, and show that increasing the molecular weight of the lamella-former at a constant ratio of its hydrophilic and hydrophobic components leads to the formation of highly-curved structures even at low sphere-former concentrations. This result is explained using a simple argument based on the effective volumes of the two sections of the diblock and is reproduced in a coarse-grained mean-field model: self-consistent field theory (SCFT). Using further SCFT calculations, we study the distribution of the two copolymer species within the individual aggregates and discuss how this affects the self-assembled structures. We also investigate a binary mixture of lamella-formers of different molecular weights, and find that this system forms vesicles with a wall thickness intermediate to those of the vesicles formed by the two copolymers individually. This result is also reproduced using SCFT. Finally, a mixture of sphere-former and a copolymer with a large hydrophobic block is shown to form a range of structures, including novel elongated vesicles.