Structure of bottle-brush polymers in solution: A Monte Carlo test of models for the scattering function

TL;DR

This study uses Monte Carlo simulations to analyze the structure of bottle-brush polymers in solution, testing and improving models that interpret scattering data to reveal internal density profiles.

Contribution

It provides detailed simulation data for various bottle-brush configurations and critically evaluates existing phenomenological models for scattering analysis.

Findings

Simulation results validate some aspects of current models.

Identifies limitations in models for inhomogeneous structures.

Suggests improvements for interpreting experimental scattering data.

Abstract

Extensive Monte Carlo results are presented for a lattice model of a bottle-brush polymer under good solvent or Theta solvent conditions. Varying the side chain length, backbone length, and the grafting density for a rigid straight backbone, both radial density profiles of monomers and side chain ends are obtained, as well as structure factors describing the scattering from a single side chain and from the total bottle-brush polymer. To describe the structure in the interior of a very long bottle-brush, a periodic boundary condition in the direction along the backbone is used, and to describe effects due to the finiteness of the backbone length, a second set of simulations with free ends of the backbone is performed. In the latter case, the inhomogeneity of the structure in the direction along the backbone is carefully investigated. We use these results to test various phenomenological models that have been proposed to interpret experimental scattering data for bottle-brush macromolecules. These models aim to extract information on the radial density profile of a bottle-brush from the total scattering via suitable convolution approximations. Possibilities to improve such models, guided by our simulation results, are discussed.