Mesophase formation in two-component cylindrical bottle-brush polymers

TL;DR

This paper investigates microphase separation in two-component cylindrical bottle-brush polymers under poor solvent conditions, combining theoretical modeling based on block copolymer analogy and molecular dynamics simulations to understand ordering phenomena.

Contribution

It extends Leibler's theory to cylindrical bottle-brush polymers and provides simulation evidence for microphase separation and Janus cylinder formation in these systems.

Findings

Short-range order and microphase separation along the cylinder axis.

Wavelength of microphase separation proportional to side chain gyration radius.

Microphase separation occurs across a wide range of temperatures and grafting densities.

Abstract

When two types of side chains (A,B) are densely grafted to a (stiff) backbone and the resulting bottle-brush polymer is in a solution under poor solvent conditions, an incompatibility between A and B leads to microphase separation in the resulting cylindrical brush. The possible types of ordering are reminiscent of the ordering of block copolymers in cylindrical confinement. Starting from this analogy, Leibler's theory of microphase separation in block copolymer melts is generalized to derive a description of the system in the weak segregation limit. Also molecular dynamics simulation results of a corresponding coarse-grained bead-spring model are presented. Using side chain lengths up to N = 50 effective monomers, the ratio of the Lennard-Jones energy parameter between unlike monomers $(\epsilon_{AB})$ and monomers of the same kind $(\epsilon _{AA} = \epsilon_{BB})$ is varied. Various correlation functions are analyzed to study the conditions when (local) Janus cylinder-type ordering and when (local) microphase separation in the direction along the cylinder axis occurs. Both the analytical theory and the simulations give evidence for short range order due to a tendency towards microphase separation in the axial direction, with a wavelength proportional to the side chain gyration radius, irrespective of temperature and grafting density, for a wide range of these parameters.