Undulated cylinders of charged diblock copolymers

TL;DR

This paper investigates the formation and stability of undulated cylindrical structures in charged diblock copolymers, revealing kinetic trapping phenomena influenced by charge and salinity levels.

Contribution

It introduces a model for the shape of cylinder ends and analyzes the free energy barriers, highlighting the kinetic trapping of undulated cylinders in charged diblock copolymer solutions.

Findings

Undulated cylinders are metastable and kinetically trapped.

High charge and low salinity reduce the energy barrier for transition.

Spheres become thermodynamically favorable beyond certain conditions.

Abstract

We study the cylinder to sphere morphological transition of diblock copolymers in aqueous solution with a hydrophobic block and a charged block. We find a metastable undulated cylinder configuration for a range of charge and salt concentrations which, nevertheless, occurs above the threshold where spheres are thermodynamically favorable. By modeling the shape of the cylinder ends, we find that the free energy barrier for the transition from cylinders to spheres is quite large and that this barrier falls significantly in the limit of high polymer charge and low solution salinity. This suggests that observed undulated cylinder phases are kinetically trapped structures.