One- and two-component bottle-brush polymers: simulations compared to theoretical predictions

TL;DR

This study compares theoretical predictions and simulations for bottle-brush polymers, revealing limitations of scaling laws under typical conditions and exploring phase separation in two-component systems influenced by solvent quality.

Contribution

It provides a comprehensive comparison between scaling theories, self-consistent field calculations, and Monte Carlo simulations for both single- and two-component bottle-brush polymers.

Findings

Weak side chain stretching under typical conditions limits scaling law applicability.

Two-component polymers exhibit local rather than global phase separation.

Solvent quality controls the microphase separation length scale.

Abstract

Scaling predictions and results from self-consistent field calculations for bottle-brush polymers with a rigid backbone and flexible side chains under good solvent conditions are summarized and their validity and applicability is assessed by a comparison with Monte Carlo simulations of a simple lattice model. It is shown that under typical conditions, as they are also present in experiments, only a rather weak stretching of the side chains is realized, and then the scaling predictions based on the extension of the Daoud-Cotton blob picture are not applicable. Also two-component bottle brush polymers are considered, where two types (A,B) of side chains are grafted, assuming that monomers of different kind repel each other. In this case, variable solvent quality is allowed for, such that for poor solvent conditions rather dense cylinder-like structures result. Theories predict ``Janus Cylinder''-type phase separation along the backbone in this case. The Monte Carlo simulations, using the pruned-enriched Rosenbluth method (PERM) then are restricted to rather short side chain length. Nevertheless, evidence is obtained that the phase separation between an A-rich part of the cylindrical molecule and a B-rich part can only occur locally. The correlation length of this microphase separation can be controlled by the solvent quality. This lack of a phase transition is interpreted by an analogy with models for ferromagnets in one space dimension.