Molecular dynamics simulations of single-component bottle-brush polymers with a flexible backbone under poor solvent conditions

TL;DR

This study uses molecular dynamics simulations to explore how single-component bottle-brush polymers with flexible backbones behave under poor solvent conditions, revealing how temperature, side chain length, and grafting density influence their conformations.

Contribution

It provides new insights into the conformational transitions of flexible backbone bottle-brush polymers under poor solvent conditions, highlighting the effects of temperature, side chain length, and grafting density.

Findings

Longer side chains increase spherical symmetry.

Collapsed chains are governed by total monomer number.

Configurations vary between coil-like and brush-like depending on parameters.

Abstract

Conformations of a single-component bottle-brush polymer with a fully flexible backbone under poor solvent conditions are studied by molecular-dynamics simulations, using a coarse-grained bead-spring model with side chains of up to N=40 effective monomers. By variation of the solvent quality and the grafting density $\sigma$ with which side chains are grafted onto the flexible backbone, we study for backbone lengths of up to $N_b=100$ the crossover from the brush/coil regime to the dense collapsed state. At lower temperatures, where collapsed chains with a constant monomer density are observed, the choice of the above parameters does not play any role and it is the total number of monomers that defines the dimensions of the chains. Furthermore, bottle-brush polymers with longer side chains possess higher spherical symmetry compared to chains with lower side-chain lengths in contrast to what one may intuitively expect, as the stretching of the side chains is less important than the increase of their length. At higher temperatures, always below the Theta ($\Theta$) temperature, coil-like configurations, similar to a single polymer chain, or brush-like configurations, similar to a homogeneous cylindrical bottle-brush polymer with a rigid backbone, are observed, depending on the choice of the particular parameters $N$ and $\sigma$. In the crossover regime between the collapsed state (globule) and the coil/brush regime the acylindricity increases, whereas for temperatures outside of this range, bottle-brush polymers maintain a highly cylindrical symmetry in all configurational states.